Lorenzo Stoakes [Wed, 22 Mar 2023 20:18:58 +0000 (20:18 +0000)]
mm/mmap/vma_merge: fold curr, next assignment logic
Use find_vma_intersection() and vma_lookup() to both simplify the logic
and to fold the end == next->vm_start condition into one block.
This groups all of the simple range checks together and establishes the
invariant that, if prev, curr or next are non-NULL then their positions
are as expected.
This has no functional impact.
Link: https://lkml.kernel.org/r/c6d960641b4ba58fa6ad3d07bf68c27d847963c8.1679516210.git.lstoakes@gmail.com Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com> Reviewed-by: Vlastimil Babka <vbabka@suse.cz> Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com> Cc: David Hildenbrand <david@redhat.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Vernon Yang <vernon2gm@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Lorenzo Stoakes [Tue, 21 Mar 2023 20:45:55 +0000 (20:45 +0000)]
mm/mmap/vma_merge: further improve prev/next VMA naming
Patch series "further cleanup of vma_merge()", v2.
Following on from Vlastimil Babka's patch series "cleanup vma_merge() and
improve mergeability tests" which was in turn based on Liam's prior
cleanups, this patch series introduces changes discussed in review of
Vlastimil's series and goes further in attempting to make the logic as
clear as possible.
Nearly all of this should have absolutely no functional impact, however it
does add a singular VM_WARN_ON() case.
With many thanks to Vernon for helping kick start the discussion around
simplification - abstract use of vma did indeed turn out not to be
necessary - and to Liam for his excellent suggestions which greatly
simplified things.
This patch (of 4):
Previously the ASCII diagram above vma_merge() and the accompanying
variable naming was rather confusing, however recent efforts by Liam
Howlett and Vlastimil Babka have significantly improved matters.
This patch goes a little further - replacing 'X' with 'N' which feels a
lot more natural and replacing what was 'N' with 'C' which stands for
'concurrent' VMA.
No word quite describes a VMA that has coincident start as the input span,
concurrent, abbreviated to 'curr' (and which can be thought of also as
'current') however fits intuitions well alongside prev and next.
Stephen Rothwell [Wed, 5 Apr 2023 23:02:38 +0000 (16:02 -0700)]
mm: vmalloc: fix sparc64 warning
This fixes this warning from a sparc64 defconfig build:
In file included from /home/sfr/next/next/include/linux/wait.h:11,
from /home/sfr/next/next/include/linux/swait.h:8,
from /home/sfr/next/next/include/linux/completion.h:12,
from /home/sfr/next/next/include/linux/mm_types.h:14,
from /home/sfr/next/next/include/linux/uio.h:10,
from /home/sfr/next/next/include/linux/vmalloc.h:12,
from /home/sfr/next/next/include/asm-generic/io.h:994,
from /home/sfr/next/next/arch/sparc/include/asm/io.h:22,
from /home/sfr/next/next/arch/sparc/vdso/vclock_gettime.c:18:
/home/sfr/next/next/arch/sparc/include/asm/current.h:18:30: warning: call-clobbered register used for global register variable
18 | register struct task_struct *current asm("g4");
| ^~~~~~~
Link: https://lkml.kernel.org/r/20230320144721.663280c3@canb.auug.org.au Fixes: 4e29dd9708cb ("mm: vmalloc: convert vread() to vread_iter()") Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au> Cc: Lorenzo Stoakes <lstoakes@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Lorenzo Stoakes [Wed, 22 Mar 2023 18:57:04 +0000 (18:57 +0000)]
mm: vmalloc: convert vread() to vread_iter()
Having previously laid the foundation for converting vread() to an
iterator function, pull the trigger and do so.
This patch attempts to provide minimal refactoring and to reflect the
existing logic as best we can, for example we continue to zero portions of
memory not read, as before.
Overall, there should be no functional difference other than a performance
improvement in /proc/kcore access to vmalloc regions.
Now we have eliminated the need for a bounce buffer in read_kcore_iter(),
we dispense with it, and try to write to user memory optimistically but
with faults disabled via copy_page_to_iter_nofault(). We already have
preemption disabled by holding a spin lock. We continue faulting in until
the operation is complete.
Additionally, we must account for the fact that at any point a copy may
fail (most likely due to a fault not being able to occur), we exit
indicating fewer bytes retrieved than expected.
Link: https://lkml.kernel.org/r/941f88bc5ab928e6656e1e2593b91bf0f8c81e1b.1679511146.git.lstoakes@gmail.com Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com> Reviewed-by: Baoquan He <bhe@redhat.com> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: David Hildenbrand <david@redhat.com> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jiri Olsa <jolsa@kernel.org> Cc: Liu Shixin <liushixin2@huawei.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Uladzislau Rezki (Sony) <urezki@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Lorenzo Stoakes [Wed, 22 Mar 2023 18:57:03 +0000 (18:57 +0000)]
iov_iter: add copy_page_to_iter_nofault()
Provide a means to copy a page to user space from an iterator, aborting if
a page fault would occur. This supports compound pages, but may be passed
a tail page with an offset extending further into the compound page, so we
cannot pass a folio.
This allows for this function to be called from atomic context and _try_
to user pages if they are faulted in, aborting if not.
The function does not use _copy_to_iter() in order to not specify
might_fault(), this is similar to copy_page_from_iter_atomic().
This is being added in order that an iteratable form of vread() can be
implemented while holding spinlocks.
Link: https://lkml.kernel.org/r/19734729defb0f498a76bdec1bef3ac48a3af3e8.1679511146.git.lstoakes@gmail.com Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com> Reviewed-by: Baoquan He <bhe@redhat.com> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: David Hildenbrand <david@redhat.com> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jiri Olsa <jolsa@kernel.org> Cc: Liu Shixin <liushixin2@huawei.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Uladzislau Rezki (Sony) <urezki@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Lorenzo Stoakes [Wed, 22 Mar 2023 18:57:02 +0000 (18:57 +0000)]
fs/proc/kcore: convert read_kcore() to read_kcore_iter()
For the time being we still use a bounce buffer for vread(), however in
the next patch we will convert this to interact directly with the iterator
and eliminate the bounce buffer altogether.
Link: https://lkml.kernel.org/r/ebe12c8d70eebd71f487d80095605f3ad0d1489c.1679511146.git.lstoakes@gmail.com Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com> Reviewed-by: David Hildenbrand <david@redhat.com> Reviewed-by: Baoquan He <bhe@redhat.com> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jiri Olsa <jolsa@kernel.org> Cc: Liu Shixin <liushixin2@huawei.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Uladzislau Rezki (Sony) <urezki@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Lorenzo Stoakes [Wed, 22 Mar 2023 18:57:01 +0000 (18:57 +0000)]
fs/proc/kcore: avoid bounce buffer for ktext data
Patch series "convert read_kcore(), vread() to use iterators", v8.
While reviewing Baoquan's recent changes to permit vread() access to
vm_map_ram regions of vmalloc allocations, Willy pointed out [1] that it
would be nice to refactor vread() as a whole, since its only user is
read_kcore() and the existing form of vread() necessitates the use of a
bounce buffer.
This patch series does exactly that, as well as adjusting how we read the
kernel text section to avoid the use of a bounce buffer in this case as
well.
This has been tested against the test case which motivated Baoquan's
changes in the first place [2] which continues to function correctly, as
do the vmalloc self tests.
This patch (of 4):
Commit df04abfd181a ("fs/proc/kcore.c: Add bounce buffer for ktext data")
introduced the use of a bounce buffer to retrieve kernel text data for
/proc/kcore in order to avoid failures arising from hardened user copies
enabled by CONFIG_HARDENED_USERCOPY in check_kernel_text_object().
We can avoid doing this if instead of copy_to_user() we use
_copy_to_user() which bypasses the hardening check. This is more
efficient than using a bounce buffer and simplifies the code.
We do so as part an overall effort to eliminate bounce buffer usage in the
function with an eye to converting it an iterator read.
This function no longer exists, however the prot != vma->vm_page_prot case
discussion has been retained and moved to vmf_insert_pfn_prot() so refer
to this instead.
Link: https://lkml.kernel.org/r/db403b3622b94a87bd93528cc1d6b44ae88adcdd.1678661628.git.lstoakes@gmail.com Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com> Reviewed-by: Christian König <christian.koenig@amd.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com> Cc: Aaron Tomlin <atomlin@atomlin.com> Cc: Christoph Lameter <cl@linux.com> Cc: Frederic Weisbecker <frederic@kernel.org> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Huacai Chen <chenhuacai@kernel.org> Cc: Marcelo Tosatti <mtosatti@redhat.com> Cc: Peter Xu <peterx@redhat.com> Cc: "Russell King (Oracle)" <linux@armlinux.org.uk> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Lorenzo Stoakes [Sun, 12 Mar 2023 23:40:14 +0000 (23:40 +0000)]
mm: remove vmf_insert_pfn_xxx_prot() for huge page-table entries
This functionality's sole user, the drm ttm module, removed support for it
in commit 0d979509539e ("drm/ttm: remove ttm_bo_vm_insert_huge()") as the
whole approach is currently unworkable without a PMD/PUD special bit and
updates to GUP.
Link: https://lkml.kernel.org/r/604c2ad79659d4b8a6e3e1611c6219d5d3233988.1678661628.git.lstoakes@gmail.com Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com> Cc: Christian König <christian.koenig@amd.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com> Cc: Aaron Tomlin <atomlin@atomlin.com> Cc: Christoph Lameter <cl@linux.com> Cc: Frederic Weisbecker <frederic@kernel.org> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Huacai Chen <chenhuacai@kernel.org> Cc: Marcelo Tosatti <mtosatti@redhat.com> Cc: Peter Xu <peterx@redhat.com> Cc: "Russell King (Oracle)" <linux@armlinux.org.uk> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Lorenzo Stoakes [Sun, 12 Mar 2023 23:40:13 +0000 (23:40 +0000)]
mm: remove unused vmf_insert_mixed_prot()
Patch series "Remove drm/ttm-specific mm changes".
Functionality was added specifically for the DRM TTM driver to support
mapping memory for VM_MIXEDMAP VMAs with customised protection flags,
however this has now been rolled back as issues were found with this
approach.
This series removes the mm changes too, retaining some of the useful
comments.
This patch (of 3):
The sole user of vmf_insert_mixed_prot(), the drm ttm module, stopped
using this in commit f91142c62161 ("drm/ttm: nuke VM_MIXEDMAP on BO
mappings v3") citing use of VM_MIXEDMAP in this case being terribly
broken.
Remove this now-dead code and references to it, but retain the useful
description of the prot != vma->vm_page_prot case, moving it to
vmf_insert_pfn_prot() instead.
Link: https://lkml.kernel.org/r/cover.1678661628.git.lstoakes@gmail.com Link: https://lkml.kernel.org/r/a069644388e6f1593a7020d15840e6fc9f39bcaf.1678661628.git.lstoakes@gmail.com Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com> Cc: Christian König <christian.koenig@amd.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com> Cc: Aaron Tomlin <atomlin@atomlin.com> Cc: Christoph Lameter <cl@linux.com> Cc: Frederic Weisbecker <frederic@kernel.org> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Huacai Chen <chenhuacai@kernel.org> Cc: Marcelo Tosatti <mtosatti@redhat.com> Cc: Peter Xu <peterx@redhat.com> Cc: "Russell King (Oracle)" <linux@armlinux.org.uk> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tomas Mudrunka [Tue, 21 Mar 2023 10:34:30 +0000 (11:34 +0100)]
mm/memtest: add results of early memtest to /proc/meminfo
Currently the memtest results were only presented in dmesg.
When running a large fleet of devices without ECC RAM it's currently not
easy to do bulk monitoring for memory corruption. You have to parse
dmesg, but that's a ring buffer so the error might disappear after some
time. In general I do not consider dmesg to be a great API to query RAM
status.
In several companies I've seen such errors remain undetected and cause
issues for way too long. So I think it makes sense to provide a
monitoring API, so that we can safely detect and act upon them.
This adds /proc/meminfo entry which can be easily used by scripts.
Mike Rapoport (IBM) [Tue, 21 Mar 2023 17:05:09 +0000 (19:05 +0200)]
init,mm: fold late call to page_ext_init() to page_alloc_init_late()
When deferred initialization of struct pages is enabled, page_ext_init()
must be called after all the deferred initialization is done, but there is
no point to keep it a separate call from kernel_init_freeable() right
after page_alloc_init_late().
Fold the call to page_ext_init() into page_alloc_init_late() and localize
deferred_struct_pages variable.
Link: https://lkml.kernel.org/r/20230321170513.2401534-11-rppt@kernel.org Signed-off-by: Mike Rapoport (IBM) <rppt@kernel.org> Reviewed-by: David Hildenbrand <david@redhat.com> Reviewed-by: Vlastimil Babka <vbabka@suse.cz> Cc: Doug Berger <opendmb@gmail.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Mel Gorman <mgorman@suse.de> Cc: Michal Hocko <mhocko@kernel.org> Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Mike Rapoport (IBM) [Tue, 21 Mar 2023 17:05:03 +0000 (19:05 +0200)]
mm: handle hashdist initialization in mm/mm_init.c
The hashdist variable must be initialized before the first call to
alloc_large_system_hash() and free_area_init() looks like a better place
for it than page_alloc_init().
Move hashdist handling to mm/mm_init.c
Link: https://lkml.kernel.org/r/20230321170513.2401534-5-rppt@kernel.org Signed-off-by: Mike Rapoport (IBM) <rppt@kernel.org> Acked-by: David Hildenbrand <david@redhat.com> Reviewed-by: Vlastimil Babka <vbabka@suse.cz> Cc: Doug Berger <opendmb@gmail.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Mel Gorman <mgorman@suse.de> Cc: Michal Hocko <mhocko@kernel.org> Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Mike Rapoport (IBM) [Tue, 21 Mar 2023 17:05:02 +0000 (19:05 +0200)]
mm: move most of core MM initialization to mm/mm_init.c
The bulk of memory management initialization code is spread all over
mm/page_alloc.c and makes navigating through page allocator functionality
difficult.
Move most of the functions marked __init and __meminit to mm/mm_init.c to
make it better localized and allow some more spare room before
mm/page_alloc.c reaches 10k lines.
No functional changes.
Link: https://lkml.kernel.org/r/20230321170513.2401534-4-rppt@kernel.org Signed-off-by: Mike Rapoport (IBM) <rppt@kernel.org> Acked-by: David Hildenbrand <david@redhat.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Cc: Doug Berger <opendmb@gmail.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Mel Gorman <mgorman@suse.de> Cc: Michal Hocko <mhocko@kernel.org> Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Mike Rapoport (IBM) [Tue, 21 Mar 2023 17:05:00 +0000 (19:05 +0200)]
mips: fix comment about pgtable_init()
Patch series "mm: move core MM initialization to mm/mm_init.c", v2.
This set moves most of the core MM initialization to mm/mm_init.c.
This largely includes free_area_init() and its helpers, functions used at
boot time, mm_init() from init/main.c and some of the functions it calls.
Aside from gaining some more space before mm/page_alloc.c hits 10k lines,
this makes mm/page_alloc.c to be mostly about buddy allocator and moves
the init code out of the way, which IMO improves maintainability.
Besides, this allows to move a couple of declarations out of include/linux
and make them private to mm/.
And as an added bonus there a slight decrease in vmlinux size. For
tinyconfig and defconfig on x86 I've got
tinyconfig:
text data bss dec hex filename
853206 289376 12001282342710 23bf36 a/vmlinux
853198 289344 12001282342670 23bf0e b/vmlinux
Lorenzo Stoakes [Tue, 21 Mar 2023 18:09:55 +0000 (18:09 +0000)]
MAINTAINERS: add Lorenzo as vmalloc reviewer
I have recently been involved in both reviewing and submitting patches to
the vmalloc code in mm and would be willing and happy to help out with
review going forward if it would be helpful!
Marcelo Tosatti [Mon, 20 Mar 2023 18:03:45 +0000 (15:03 -0300)]
vmstat: add pcp remote node draining via cpu_vm_stats_fold
Large NUMA systems might have significant portions of system memory to be
trapped in pcp queues. The number of pcp is determined by the number of
processors and nodes in a system. A system with 4 processors and 2 nodes
has 8 pcps which is okay. But a system with 1024 processors and 512 nodes
has 512k pcps with a high potential for large amount of memory being
caught in them.
Enable remote node draining for the CONFIG_HAVE_CMPXCHG_LOCAL case, where
vmstat_shepherd will perform the aging and draining via cpu_vm_stats_fold.
Link: https://lkml.kernel.org/r/20230320180745.858515310@redhat.com Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com> Suggested-by: Vlastimil Babka <vbabka@suse.cz> Cc: Aaron Tomlin <atomlin@atomlin.com> Cc: Christoph Lameter <cl@linux.com> Cc: Frederic Weisbecker <frederic@kernel.org> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Huacai Chen <chenhuacai@kernel.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Peter Xu <peterx@redhat.com> Cc: "Russell King (Oracle)" <linux@armlinux.org.uk> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Marcelo Tosatti [Mon, 20 Mar 2023 18:03:43 +0000 (15:03 -0300)]
mm/vmstat: switch vmstat shepherd to flush per-CPU counters remotely
With a task that busy loops on a given CPU, the kworker interruption to
execute vmstat_update is undesired and may exceed latency thresholds for
certain applications.
switches. In the case of a virtualized CPU, and the vmstat_update
interruption in the host (of a qemu-kvm vcpu), the latency penalty
observed in the guest is higher than 50us, violating the acceptable
latency threshold for certain applications.
To fix this, now that the counters are modified via cmpxchg both CPU
locally (via the account functions), and remotely (via cpu_vm_stats_fold),
its possible to switch vmstat_shepherd to perform the per-CPU vmstats
folding remotely.
Link: https://lkml.kernel.org/r/20230320180745.807656081@redhat.com Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com> Cc: Aaron Tomlin <atomlin@atomlin.com> Cc: Christoph Lameter <cl@linux.com> Cc: Frederic Weisbecker <frederic@kernel.org> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Huacai Chen <chenhuacai@kernel.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Peter Xu <peterx@redhat.com> Cc: "Russell King (Oracle)" <linux@armlinux.org.uk> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Marcelo Tosatti [Mon, 20 Mar 2023 18:03:40 +0000 (15:03 -0300)]
mm/vmstat: switch counter modification to cmpxchg
In preparation for switching vmstat shepherd to flush per-CPU counters
remotely, switch the __{mod,inc,dec} functions that modify the counters to
use cmpxchg.
To facilitate reviewing, functions are ordered in the text file, as:
To test the performance difference, a page allocator microbenchmark:
https://github.com/netoptimizer/prototype-kernel/blob/master/kernel/mm/bench/page_bench01.c
with loops=1000000 was used, on Intel Core i7-11850H @ 2.50GHz.
For the single_page_alloc_free test, which does
/** Loop to measure **/
for (i = 0; i < rec->loops; i++) {
my_page = alloc_page(gfp_mask);
if (unlikely(my_page == NULL))
return 0;
__free_page(my_page);
}
Unit is cycles.
Vanilla Patched Diff
115.25 117 1.4%
Link: https://lkml.kernel.org/r/20230320180745.733575720@redhat.com Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com> Cc: Aaron Tomlin <atomlin@atomlin.com> Cc: Christoph Lameter <cl@linux.com> Cc: Frederic Weisbecker <frederic@kernel.org> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Huacai Chen <chenhuacai@kernel.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Peter Xu <peterx@redhat.com> Cc: "Russell King (Oracle)" <linux@armlinux.org.uk> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Marcelo Tosatti [Mon, 20 Mar 2023 18:03:37 +0000 (15:03 -0300)]
this_cpu_cmpxchg: x86: switch this_cpu_cmpxchg to locked, add _local function
Goal is to have vmstat_shepherd to transfer from per-CPU counters to
global counters remotely. For this, an atomic this_cpu_cmpxchg is
necessary.
Following the kernel convention for cmpxchg/cmpxchg_local, change x86's
this_cpu_cmpxchg_ helpers to be atomic. and add this_cpu_cmpxchg_local_
helpers which are not atomic.
Link: https://lkml.kernel.org/r/20230320180745.658574087@redhat.com Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com> Cc: Aaron Tomlin <atomlin@atomlin.com> Cc: Christoph Lameter <cl@linux.com> Cc: Frederic Weisbecker <frederic@kernel.org> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Huacai Chen <chenhuacai@kernel.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Peter Xu <peterx@redhat.com> Cc: "Russell King (Oracle)" <linux@armlinux.org.uk> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Marcelo Tosatti [Mon, 20 Mar 2023 18:03:34 +0000 (15:03 -0300)]
this_cpu_cmpxchg: ARM64: switch this_cpu_cmpxchg to locked, add _local function
Goal is to have vmstat_shepherd to transfer from per-CPU counters to
global counters remotely. For this, an atomic this_cpu_cmpxchg is
necessary.
Following the kernel convention for cmpxchg/cmpxchg_local, change ARM's
this_cpu_cmpxchg_ helpers to be atomic, and add this_cpu_cmpxchg_local_
helpers which are not atomic.
Link: https://lkml.kernel.org/r/20230320180745.582248645@redhat.com Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com> Cc: Aaron Tomlin <atomlin@atomlin.com> Cc: Christoph Lameter <cl@linux.com> Cc: Frederic Weisbecker <frederic@kernel.org> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Huacai Chen <chenhuacai@kernel.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Peter Xu <peterx@redhat.com> Cc: "Russell King (Oracle)" <linux@armlinux.org.uk> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Marcelo Tosatti [Mon, 20 Mar 2023 18:03:33 +0000 (15:03 -0300)]
vmstat: allow_direct_reclaim should use zone_page_state_snapshot
Patch series "fold per-CPU vmstats remotely", v7.
This patch series addresses the following two problems:
1. A customer provided evidence indicating that a process
was stalled in direct reclaim:
- The process was trapped in throttle_direct_reclaim().
The function wait_event_killable() was called to wait condition
allow_direct_reclaim(pgdat) for current node to be true.
The allow_direct_reclaim(pgdat) examined the number of free pages
on the node by zone_page_state() which just returns value in
zone->vm_stat[NR_FREE_PAGES].
- On node #1, zone->vm_stat[NR_FREE_PAGES] was 0.
However, the freelist on this node was not empty.
- This inconsistent of vmstat value was caused by percpu vmstat on
nohz_full cpus. Every increment/decrement of vmstat is performed
on percpu vmstat counter at first, then pooled diffs are cumulated
to the zone's vmstat counter in timely manner. However, on nohz_full
cpus (in case of this customer's system, 48 of 52 cpus) these pooled
diffs were not cumulated once the cpu had no event on it so that
the cpu started sleeping infinitely.
I checked percpu vmstat and found there were total 69 counts not
cumulated to the zone's vmstat counter yet.
- In this situation, kswapd did not help the trapped process.
In pgdat_balanced(), zone_wakermark_ok_safe() examined the number
of free pages on the node by zone_page_state_snapshot() which
checks pending counts on percpu vmstat.
Therefore kswapd could know there were 69 free pages correctly.
Since zone->_watermark = {8, 20, 32}, kswapd did not work because
69 was greater than 32 as high watermark.
2. With a task that busy loops on a given CPU,
the kworker interruption to execute vmstat_update
is undesired and may exceed latency thresholds
for certain applications.
By having vmstat_shepherd flush the per-CPU counters to the
global counters from remote CPUs.
This is done using cmpxchg to manipulate the counters,
both CPU locally (via the account functions),
and remotely (via cpu_vm_stats_fold).
Thanks to Aaron Tomlin for diagnosing issue 1 and writing
the initial patch series.
switches. In the case of a virtualized CPU, and the vmstat_update
interruption in the host (of a qemu-kvm vcpu), the latency penalty
observed in the guest is higher than 50us, violating the acceptable
latency threshold for certain applications.
This patch (of 13):
A customer provided evidence indicating that a process
was stalled in direct reclaim:
- The process was trapped in throttle_direct_reclaim().
The function wait_event_killable() was called to wait condition
allow_direct_reclaim(pgdat) for current node to be true.
The allow_direct_reclaim(pgdat) examined the number of free pages
on the node by zone_page_state() which just returns value in
zone->vm_stat[NR_FREE_PAGES].
- On node #1, zone->vm_stat[NR_FREE_PAGES] was 0.
However, the freelist on this node was not empty.
- This inconsistent of vmstat value was caused by percpu vmstat on
nohz_full cpus. Every increment/decrement of vmstat is performed
on percpu vmstat counter at first, then pooled diffs are cumulated
to the zone's vmstat counter in timely manner. However, on nohz_full
cpus (in case of this customer's system, 48 of 52 cpus) these pooled
diffs were not cumulated once the cpu had no event on it so that
the cpu started sleeping infinitely.
I checked percpu vmstat and found there were total 69 counts not
cumulated to the zone's vmstat counter yet.
- In this situation, kswapd did not help the trapped process.
In pgdat_balanced(), zone_wakermark_ok_safe() examined the number
of free pages on the node by zone_page_state_snapshot() which
checks pending counts on percpu vmstat.
Therefore kswapd could know there were 69 free pages correctly.
Since zone->_watermark = {8, 20, 32}, kswapd did not work because
69 was greater than 32 as high watermark.
Change allow_direct_reclaim to use zone_page_state_snapshot, which
allows a more precise version of the vmstat counters to be used.
allow_direct_reclaim will only be called from try_to_free_pages,
which is not a hot path.
Link: https://lkml.kernel.org/r/20230320180332.102837832@redhat.com Link: https://lkml.kernel.org/r/20230320180745.556821285@redhat.com Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com> Suggested-by: Michal Hocko <mhocko@suse.com> Acked-by: Michal Hocko <mhocko@suse.com> Cc: Aaron Tomlin <atomlin@atomlin.com> Cc: Christoph Lameter <cl@linux.com> Cc: Frederic Weisbecker <frederic@kernel.org> Cc: Heiko Carstens <hca@linux.ibm.com> Cc: Huacai Chen <chenhuacai@kernel.org> Cc: Michal Hocko <mhocko@suse.com> Cc: "Russell King (Oracle)" <linux@armlinux.org.uk> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Peter Xu <peterx@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Mike Rapoport (IBM) [Sun, 19 Mar 2023 11:42:14 +0000 (13:42 +0200)]
mm: move get_page_from_free_area() to mm/page_alloc.c
The get_page_from_free_area() helper is only used in mm/page_alloc.c so
move it there to reduce noise in include/linux/mmzone.h
Link: https://lkml.kernel.org/r/20230319114214.2133332-1-rppt@kernel.org Signed-off-by: Mike Rapoport (IBM) <rppt@kernel.org> Reviewed-by: Lorenzo Stoakes <lstoakes@gmail.com> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Lorenzo Stoakes [Fri, 17 Mar 2023 21:58:25 +0000 (21:58 +0000)]
mm: refactor do_fault_around()
Patch series "Refactor do_fault_around()"
Refactor do_fault_around() to avoid bitwise tricks and rather difficult to
follow logic. Additionally, prefer fault_around_pages to
fault_around_bytes as the operations are performed at a base page
granularity.
This patch (of 2):
The existing logic is confusing and fails to abstract a number of bitwise
tricks.
Use ALIGN_DOWN() to perform alignment, pte_index() to obtain a PTE index
and represent the address range using PTE offsets, which naturally make it
clear that the operation is intended to occur within only a single PTE and
prevent spanning of more than one page table.
We rely on the fact that fault_around_bytes will always be page-aligned,
at least one page in size, a power of two and that it will not exceed
PAGE_SIZE * PTRS_PER_PTE in size (i.e. the address space mapped by a
PTE). These are all guaranteed by fault_around_bytes_set().
Michal Hocko [Fri, 17 Mar 2023 13:44:48 +0000 (14:44 +0100)]
memcg: do not drain charge pcp caches on remote isolated cpus
Leonardo Bras has noticed that pcp charge cache draining might be
disruptive on workloads relying on 'isolated cpus', a feature commonly
used on workloads that are sensitive to interruption and context switching
such as vRAN and Industrial Control Systems.
There are essentially two ways how to approach the issue. We can either
allow the pcp cache to be drained on a different rather than a local cpu
or avoid remote flushing on isolated cpus.
The current pcp charge cache is really optimized for high performance and
it always relies to stick with its cpu. That means it only requires
local_lock (preempt_disable on !RT) and draining is handed over to pcp WQ
to drain locally again.
The former solution (remote draining) would require to add an additional
locking to prevent local charges from racing with the draining. This adds
an atomic operation to otherwise simple arithmetic fast path in the
try_charge path. Another concern is that the remote draining can cause a
lock contention for the isolated workloads and therefore interfere with it
indirectly via user space interfaces.
Another option is to avoid draining scheduling on isolated cpus
altogether. That means that those remote cpus would keep their charges
even after drain_all_stock returns. This is certainly not optimal either
but it shouldn't really cause any major problems. In the worst case (many
isolated cpus with charges - each of them with MEMCG_CHARGE_BATCH i.e 64
page) the memory consumption of a memcg would be artificially higher than
can be immediately used from other cpus.
Theoretically a memcg OOM killer could be triggered pre-maturely.
Currently it is not really clear whether this is a practical problem
though. Tight memcg limit would be really counter productive to cpu
isolated workloads pretty much by definition because any memory reclaimed
induced by memcg limit could break user space timing expectations as those
usually expect execution in the userspace most of the time.
Also charges could be left behind on memcg removal. Any future charge on
those isolated cpus will drain that pcp cache so this won't be a permanent
leak.
Considering cons and pros of both approaches this patch is implementing
the second option and simply do not schedule remote draining if the target
cpu is isolated. This solution is much more simpler. It doesn't add any
new locking and it is more more predictable from the user space POV.
Should the pre-mature memcg OOM become a real life problem, we can revisit
this decision.
Link: https://lkml.kernel.org/r/20230317134448.11082-3-mhocko@kernel.org Signed-off-by: Michal Hocko <mhocko@suse.com> Suggested-by: Roman Gushchin <roman.gushchin@linux.dev> Acked-by: Roman Gushchin <roman.gushchin@linux.dev> Reported-by: Leonardo Bras <leobras@redhat.com> Acked-by: Shakeel Butt <shakeelb@google.com> Cc: Marcelo Tosatti <mtosatti@redhat.com> Cc: Muchun Song <muchun.song@linux.dev> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Frederic Weisbecker <frederic@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Frederic Weisbecker [Fri, 17 Mar 2023 13:44:47 +0000 (14:44 +0100)]
sched/isolation: add cpu_is_isolated() API
Patch series "memcg, cpuisol: do not interfere pcp cache charges draining
with cpuisol workloads".
Leonardo has reported [1] that pcp memcg charge draining can interfere
with cpu isolated workloads. The said draining is done from a WQ context
with a pcp worker scheduled on each CPU which holds any cached charges for
a specific memcg hierarchy. Operation is not really a common operation
[2]. It can be triggered from the userspace though so some care is
definitely due.
Leonardo has tried to address the issue by allowing remote charge draining
[3]. This approach requires an additional locking to synchronize pcp
caches sync from a remote cpu from local pcp consumers. Even though the
proposed lock was per-cpu there is still potential for contention and less
predictable behavior.
This patchset addresses the issue from a different angle. Rather than
dealing with a potential synchronization, cpus which are isolated are
simply never scheduled to be drained. This means that a small amount of
charges could be laying around and waiting for a later use or they are
flushed when a different memcg is charged from the same cpu. More details
are in patch 2. The first patch from Frederic is implementing an
abstraction to tell whether a specific cpu has been isolated and therefore
require a special treatment.
This patch (of 2):
Provide this new API to check if a CPU has been isolated either through
isolcpus= or nohz_full= kernel parameter.
It aims at avoiding kernel load deemed to be safely spared on CPUs running
sensitive workload that can't bear any disturbance, such as pcp cache
draining.
Link: https://lkml.kernel.org/r/20230317134448.11082-1-mhocko@kernel.org Link: https://lkml.kernel.org/r/20230317134448.11082-2-mhocko@kernel.org Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Michal Hocko <mhocko@suse.com> Suggested-by: Michal Hocko <mhocko@suse.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Marcelo Tosatti <mtosatti@redhat.com> Cc: Muchun Song <muchun.song@linux.dev> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Roman Gushchin <roman.gushchin@linux.dev> Cc: Shakeel Butt <shakeelb@google.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Leonardo Bras <leobras@redhat.com> Cc: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Baolin Wang [Thu, 16 Mar 2023 11:06:47 +0000 (19:06 +0800)]
mm: compaction: fix the possible deadlock when isolating hugetlb pages
When trying to isolate a migratable pageblock, it can contain several
normal pages or several hugetlb pages (e.g. CONT-PTE 64K hugetlb on arm64)
in a pageblock. That means we may hold the lru lock of a normal page to
continue to isolate the next hugetlb page by isolate_or_dissolve_huge_page()
in the same migratable pageblock.
However in the isolate_or_dissolve_huge_page(), it may allocate a new hugetlb
page and dissolve the old one by alloc_and_dissolve_hugetlb_folio() if the
hugetlb's refcount is zero. That means we can still enter the direct compaction
path to allocate a new hugetlb page under the current lru lock, which
may cause possible deadlock.
To avoid this possible deadlock, we should release the lru lock when
trying to isolate a hugetbl page. Moreover it does not make sense to take
the lru lock to isolate a hugetlb, which is not in the lru list.
Link: https://lkml.kernel.org/r/7ab3bffebe59fb419234a68dec1e4572a2518563.1678962352.git.baolin.wang@linux.alibaba.com Fixes: 369fa227c219 ("mm: make alloc_contig_range handle free hugetlb pages") Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com> Reviewed-by: Vlastimil Babka <vbabka@suse.cz> Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com> Acked-by: Mel Gorman <mgorman@techsingularity.net> Cc: Oscar Salvador <osalvador@suse.de> Cc: William Lam <william.lam@bytedance.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Baolin Wang [Thu, 16 Mar 2023 11:06:46 +0000 (19:06 +0800)]
mm: compaction: consider the number of scanning compound pages in isolate fail path
commit b717d6b93b54 ("mm: compaction: include compound page count for
scanning in pageblock isolation") added compound page statistics for
scanning in pageblock isolation, to make sure the number of scanned pages
is always larger than the number of isolated pages when isolating
mirgratable or free pageblock.
However, when failing to isolate the pages when scanning the migratable or
free pageblocks, the isolation failure path did not consider the scanning
statistics of the compound pages, which result in showing the incorrect
number of scanned pages in tracepoints or in vmstats which will confuse
people about the page scanning pressure in memory compaction.
Thus we should take into account the number of scanning pages when failing
to isolate the compound pages to make the statistics accurate.
Link: https://lkml.kernel.org/r/73d6250a90707649cc010731aedc27f946d722ed.1678962352.git.baolin.wang@linux.alibaba.com Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com> Reviewed-by: Vlastimil Babka <vbabka@suse.cz> Acked-by: Mel Gorman <mgorman@techsingularity.net> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Oscar Salvador <osalvador@suse.de> Cc: William Lam <william.lam@bytedance.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Vlastimil Babka [Thu, 9 Mar 2023 11:12:58 +0000 (12:12 +0100)]
mm/mremap: simplify vma expansion again
This effectively reverts d014cd7c1c35 ("mm, mremap: fix mremap() expanding
for vma's with vm_ops->close()"). After the recent changes, vma_merge()
is able to handle the expansion properly even when the vma being expanded
has a vm_ops->close operation, so we don't need to special case it
anymore.
Link: https://lkml.kernel.org/r/20230309111258.24079-11-vbabka@suse.cz Signed-off-by: Vlastimil Babka <vbabka@suse.cz> Reviewed-by: Lorenzo Stoakes <lstoakes@gmail.com> Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Suren Baghdasaryan <surenb@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Vlastimil Babka [Thu, 9 Mar 2023 11:12:57 +0000 (12:12 +0100)]
mm/mmap: start distinguishing if vma can be removed in mergeability test
Since pre-git times, is_mergeable_vma() returns false for a vma with
vm_ops->close, so that no owner assumptions are violated in case the vma
is removed as part of the merge.
This check is currently very conservative and can prevent merging even
situations where vma can't be removed, such as simple expansion of
previous vma, as evidenced by commit d014cd7c1c35 ("mm, mremap: fix
mremap() expanding for vma's with vm_ops->close()")
In order to allow more merging when appropriate and simplify the code that
was made more complex by commit d014cd7c1c35, start distinguishing cases
where the vma can be really removed, and allow merging with vm_ops->close
otherwise.
As a first step, add a may_remove_vma parameter to is_mergeable_vma().
can_vma_merge_before() sets it to true, because when called from
vma_merge(), a removal of the vma is possible.
In can_vma_merge_after(), pass the parameter as false, because no
removal can occur in each of its callers:
- vma_merge() calls it on the 'prev' vma, which is never removed
- mmap_region() and do_brk_flags() call it to determine if it can expand
a vma, which is not removed
As a result, vma's with vm_ops->close may now merge with compatible ranges
in more situations than previously. We can also revert commit d014cd7c1c35 as the next step to simplify mremap code again.
Link: https://lkml.kernel.org/r/20230309111258.24079-10-vbabka@suse.cz Signed-off-by: Vlastimil Babka <vbabka@suse.cz> Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com> Cc: Lorenzo Stoakes <lstoakes@gmail.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Suren Baghdasaryan <surenb@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Vlastimil Babka [Thu, 9 Mar 2023 11:12:55 +0000 (12:12 +0100)]
mm/mmap/vma_merge: rename adj_next to adj_start
The variable 'adj_next' holds the value by which we adjust vm_start of a
vma in variable 'adjust', that's either 'next' or 'mid', so the current
name is inaccurate. Rename it to 'adj_start'.
Link: https://lkml.kernel.org/r/20230309111258.24079-8-vbabka@suse.cz Signed-off-by: Vlastimil Babka <vbabka@suse.cz> Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com> Cc: Lorenzo Stoakes <lstoakes@gmail.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Suren Baghdasaryan <surenb@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Vlastimil Babka [Thu, 9 Mar 2023 11:12:54 +0000 (12:12 +0100)]
mm/mmap/vma_merge: set mid to NULL if not applicable
There are several places where we test if 'mid' is really the area NNNN in
the diagram and the tests have two variants and are non-obvious to follow.
Instead, set 'mid' to NULL up-front if it's not the NNNN area, and
simplify the tests.
Also update the description in comment accordingly.
Link: https://lkml.kernel.org/r/20230309111258.24079-7-vbabka@suse.cz Signed-off-by: Vlastimil Babka <vbabka@suse.cz> Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com> Cc: Lorenzo Stoakes <lstoakes@gmail.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Suren Baghdasaryan <surenb@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Vlastimil Babka [Thu, 9 Mar 2023 11:12:52 +0000 (12:12 +0100)]
mm/mmap/vma_merge: use the proper vma pointer in case 4
Almost all cases now use the 'next' pointer for the vma following the
merged area, and the cases diagram shows it as XXXX. Case 4 is different
as it uses 'mid' and NNNN, so change it for consistency. No functional
change.
Link: https://lkml.kernel.org/r/20230309111258.24079-5-vbabka@suse.cz Signed-off-by: Vlastimil Babka <vbabka@suse.cz> Reviewed-by: Lorenzo Stoakes <lstoakes@gmail.com> Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Suren Baghdasaryan <surenb@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Vlastimil Babka [Thu, 9 Mar 2023 11:12:51 +0000 (12:12 +0100)]
mm/mmap/vma_merge: use the proper vma pointers in cases 1 and 6
Case 1 is now shown in the comment as next vma being merged with prev, so
use 'next' instead of 'mid'. In case 1 they both point to the same vma.
As a consequence, in case 6, the dup_anon_vma() is now tried first on
'next' and then on 'mid', before it was the opposite order. This is not a
functional change, as those two vma's cannnot have a different anon_vma,
as that would have prevented the merging in the first place.
Link: https://lkml.kernel.org/r/20230309111258.24079-4-vbabka@suse.cz Signed-off-by: Vlastimil Babka <vbabka@suse.cz> Reviewed-by: Lorenzo Stoakes <lstoakes@gmail.com> Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Suren Baghdasaryan <surenb@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Vlastimil Babka [Thu, 9 Mar 2023 11:12:50 +0000 (12:12 +0100)]
mm/mmap/vma_merge: use the proper vma pointer in case 3
In case 3 we we use 'next' for everything but vma_pgoff. So use 'next'
for that as well, instead of 'mid', for consistency. Then in case 8 we
have to use 'mid' explicitly, which should also make the intent more
obvious.
Adjust the diagram for cases 1-3 in the comment to match the code - we are
using 'next' for case 3 so mark the range with XXXX instead of NNNN. For
case 2 that's a no-op as the code doesn't touch 'next' or 'mid'. For case
1 it's now wrong but that will be fixed next.
No functional change.
Link: https://lkml.kernel.org/r/20230309111258.24079-3-vbabka@suse.cz Signed-off-by: Vlastimil Babka <vbabka@suse.cz> Reviewed-by: Lorenzo Stoakes <lstoakes@gmail.com> Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Suren Baghdasaryan <surenb@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Vlastimil Babka [Thu, 9 Mar 2023 11:12:49 +0000 (12:12 +0100)]
mm/mmap/vma_merge: use only primary pointers for preparing merge
Patch series "cleanup vma_merge() and improve mergeability tests".
My initial goal here was to try making the check for vm_ops->close in
is_mergeable_vma() only be applied for vma's that would be truly removed
as part of the merge (see Patch 9). This would then allow reverting the
quick fix d014cd7c1c35 ("mm, mremap: fix mremap() expanding for vma's with
vm_ops->close()"). This was successful enough to allow the revert (Patch
10). Checks using can_vma_merge_before() are still pessimistic about
possible vma removal, and making them precise would probably complicate
the vma_merge() code too much.
Liam's 6.3-rc1 simplification of vma_merge() and removal of __vma_adjust()
was very much helpful in understanding the vma_merge() implementation and
especially when vma removals can happen, which is now very obvious. While
studing the code, I've found ways to make it hopefully even more easy to
follow, so that's the patches 1-8. That made me also notice a bug that's
now already fixed in 6.3-rc1.
This patch (of 10):
In the merging preparation part of vma_merge(), some vma pointer variables
are assigned for later execution of the merge, but also read from in the
block itself. The code is easier follow and check against the cases
diagram in the comment if the code reads only from the "primary" vma
variables prev, mid, next instead. No functional change.
Axel Rasmussen [Tue, 14 Mar 2023 22:12:50 +0000 (15:12 -0700)]
mm: userfaultfd: add UFFDIO_CONTINUE_MODE_WP to install WP PTEs
UFFDIO_COPY already has UFFDIO_COPY_MODE_WP, so when installing a new PTE
to resolve a missing fault, one can install a write-protected one. This
is useful when using UFFDIO_REGISTER_MODE_{MISSING,WP} in combination.
This was motivated by testing HugeTLB HGM [1], and in particular its
interaction with userfaultfd features. Existing userfaultfd code supports
using WP and MINOR modes together (i.e. you can register an area with
both enabled), but without this CONTINUE flag the combination is in
practice unusable.
So, add an analogous UFFDIO_CONTINUE_MODE_WP, which does the same thing as
UFFDIO_COPY_MODE_WP, but for *minor* faults.
Update the selftest to do some very basic exercising of the new flag.
Update Documentation/ to describe how these flags are used (neither the
COPY nor the new CONTINUE versions of this mode flag were described there
before).
Link: https://lkml.kernel.org/r/20230314221250.682452-5-axelrasmussen@google.com Signed-off-by: Axel Rasmussen <axelrasmussen@google.com> Acked-by: Peter Xu <peterx@redhat.com> Acked-by: Mike Rapoport (IBM) <rppt@kernel.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Hugh Dickins <hughd@google.com> Cc: Jan Kara <jack@suse.cz> Cc: Liam R. Howlett <Liam.Howlett@oracle.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Muchun Song <muchun.song@linux.dev> Cc: Nadav Amit <namit@vmware.com> Cc: Shuah Khan <shuah@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Axel Rasmussen [Tue, 14 Mar 2023 22:12:49 +0000 (15:12 -0700)]
mm: userfaultfd: combine 'mode' and 'wp_copy' arguments
Many userfaultfd ioctl functions take both a 'mode' and a 'wp_copy'
argument. In future commits we plan to plumb the flags through to more
places, so we'd be proliferating the very long argument list even further.
Let's take the time to simplify the argument list. Combine the two
arguments into one - and generalize, so when we add more flags in the
future, it doesn't imply more function arguments.
Since the modes (copy, zeropage, continue) are mutually exclusive, store
them as an integer value (0, 1, 2) in the low bits. Place combine-able
flag bits in the high bits.
This is quite similar to an earlier patch proposed by Nadav Amit
("userfaultfd: introduce uffd_flags" [1]). The main difference is that
patch only handled flags, whereas this patch *also* combines the "mode"
argument into the same type to shorten the argument list.
Link: https://lkml.kernel.org/r/20230314221250.682452-4-axelrasmussen@google.com Signed-off-by: Axel Rasmussen <axelrasmussen@google.com> Acked-by: James Houghton <jthoughton@google.com> Acked-by: Peter Xu <peterx@redhat.com> Acked-by: Mike Rapoport (IBM) <rppt@kernel.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Hugh Dickins <hughd@google.com> Cc: Jan Kara <jack@suse.cz> Cc: Liam R. Howlett <Liam.Howlett@oracle.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Muchun Song <muchun.song@linux.dev> Cc: Shuah Khan <shuah@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Axel Rasmussen [Tue, 14 Mar 2023 22:12:48 +0000 (15:12 -0700)]
mm: userfaultfd: don't pass around both mm and vma
Quite a few userfaultfd functions took both mm and vma pointers as
arguments. Since the mm is trivially accessible via vma->vm_mm, there's
no reason to pass both; it just needlessly extends the already long
argument list.
Get rid of the mm pointer, where possible, to shorten the argument list.
Link: https://lkml.kernel.org/r/20230314221250.682452-3-axelrasmussen@google.com Signed-off-by: Axel Rasmussen <axelrasmussen@google.com> Acked-by: Peter Xu <peterx@redhat.com> Acked-by: Mike Rapoport (IBM) <rppt@kernel.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Hugh Dickins <hughd@google.com> Cc: James Houghton <jthoughton@google.com> Cc: Jan Kara <jack@suse.cz> Cc: Liam R. Howlett <Liam.Howlett@oracle.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Muchun Song <muchun.song@linux.dev> Cc: Nadav Amit <namit@vmware.com> Cc: Shuah Khan <shuah@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Axel Rasmussen [Tue, 14 Mar 2023 22:12:47 +0000 (15:12 -0700)]
mm: userfaultfd: rename functions for clarity + consistency
Patch series "mm: userfaultfd: refactor and add UFFDIO_CONTINUE_MODE_WP",
v5.
- Commits 1-3 refactor userfaultfd ioctl code without behavior changes, with the
main goal of improving consistency and reducing the number of function args.
- Commit 4 adds UFFDIO_CONTINUE_MODE_WP.
This patch (of 4):
The basic problem is, over time we've added new userfaultfd ioctls, and
we've refactored the code so functions which used to handle only one case
are now re-used to deal with several cases. While this happened, we
didn't bother to rename the functions.
Similarly, as we added new functions, we cargo-culted pieces of the
now-inconsistent naming scheme, so those functions too ended up with names
that don't make a lot of sense.
A key point here is, "copy" in most userfaultfd code refers specifically
to UFFDIO_COPY, where we allocate a new page and copy its contents from
userspace. There are many functions with "copy" in the name that don't
actually do this (at least in some cases).
So, rename things into a consistent scheme. The high level idea is that
the call stack for userfaultfd ioctls becomes:
userfaultfd_ioctl
-> userfaultfd_(particular ioctl)
-> mfill_atomic_(particular kind of fill operation)
-> mfill_atomic /* loops over pages in range */
-> mfill_atomic_pte /* deals with single pages */
-> mfill_atomic_pte_(particular kind of fill operation)
-> mfill_atomic_install_pte
There are of course some special cases (shmem, hugetlb), but this is the
general structure which all function names now adhere to.
Link: https://lkml.kernel.org/r/20230314221250.682452-1-axelrasmussen@google.com Link: https://lkml.kernel.org/r/20230314221250.682452-2-axelrasmussen@google.com Signed-off-by: Axel Rasmussen <axelrasmussen@google.com> Acked-by: Peter Xu <peterx@redhat.com> Acked-by: Mike Rapoport (IBM) <rppt@kernel.org> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Hugh Dickins <hughd@google.com> Cc: James Houghton <jthoughton@google.com> Cc: Jan Kara <jack@suse.cz> Cc: Liam R. Howlett <Liam.Howlett@oracle.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Muchun Song <muchun.song@linux.dev> Cc: Nadav Amit <namit@vmware.com> Cc: Shuah Khan <shuah@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Andrew Morton [Wed, 15 Mar 2023 20:54:45 +0000 (13:54 -0700)]
mm-treewide-redefine-max_order-sanely-fix-2
fix another min_t warning
Cc: "Kirill A. Shutemov" <kirill@shutemov.name> Cc: kernel test robot <lkp@intel.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Zi Yan <ziy@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Kirill A. Shutemov [Wed, 15 Mar 2023 11:31:33 +0000 (14:31 +0300)]
mm, treewide: redefine MAX_ORDER sanely
MAX_ORDER currently defined as number of orders page allocator supports:
user can ask buddy allocator for page order between 0 and MAX_ORDER-1.
This definition is counter-intuitive and lead to number of bugs all over
the kernel.
Change the definition of MAX_ORDER to be inclusive: the range of orders
user can ask from buddy allocator is 0..MAX_ORDER now.
Link: https://lkml.kernel.org/r/20230315113133.11326-11-kirill.shutemov@linux.intel.com Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Reviewed-by: Michael Ellerman <mpe@ellerman.id.au> [powerpc] Cc: "Kirill A. Shutemov" <kirill@shutemov.name> Cc: Zi Yan <ziy@nvidia.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Kirill A. Shutemov [Wed, 15 Mar 2023 11:31:32 +0000 (14:31 +0300)]
iommu: fix MAX_ORDER usage in __iommu_dma_alloc_pages()
MAX_ORDER is not inclusive: the maximum allocation order buddy allocator
can deliver is MAX_ORDER-1.
Fix MAX_ORDER usage in __iommu_dma_alloc_pages().
Also use GENMASK() instead of hard to read "(2U << order) - 1" magic.
Link: https://lkml.kernel.org/r/20230315113133.11326-10-kirill.shutemov@linux.intel.com Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Acked-by: Robin Murphy <robin.murphy@arm.com> Reviewed-by: Jacob Pan <jacob.jun.pan@linux.intel.com> Acked-by: Joerg Roedel <jroedel@suse.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Kirill A. Shutemov [Wed, 15 Mar 2023 11:31:29 +0000 (14:31 +0300)]
perf/core: fix MAX_ORDER usage in rb_alloc_aux_page()
MAX_ORDER is not inclusive: the maximum allocation order buddy allocator
can deliver is MAX_ORDER-1.
Fix MAX_ORDER usage in rb_alloc_aux_page().
Link: https://lkml.kernel.org/r/20230315113133.11326-7-kirill.shutemov@linux.intel.com Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@redhat.com> Cc: Arnaldo Carvalho de Melo <acme@kernel.org> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> Cc: Jiri Olsa <jolsa@kernel.org> Cc: Namhyung Kim <namhyung@kernel.org> Cc: Ian Rogers <irogers@google.com> Cc: Adrian Hunter <adrian.hunter@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Kirill A. Shutemov [Wed, 15 Mar 2023 11:31:25 +0000 (14:31 +0300)]
um: fix MAX_ORDER usage in linux_main()
MAX_ORDER is not inclusive: the maximum allocation order buddy allocator
can deliver is MAX_ORDER-1.
Fix MAX_ORDER usage in linux_main().
Link: https://lkml.kernel.org/r/20230315113133.11326-3-kirill.shutemov@linux.intel.com Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Acked-by: Mike Rapoport (IBM) <rppt@kernel.org> Cc: Richard Weinberger <richard@nod.at> Cc: Anton Ivanov <anton.ivanov@cambridgegreys.com> Cc: Johannes Berg <johannes@sipsolutions.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Peter Xu [Thu, 9 Mar 2023 22:37:11 +0000 (17:37 -0500)]
selftests/mm: smoke test UFFD_FEATURE_WP_UNPOPULATED
Enable it by default on the stress test, and add some smoke tests for the
pte markers on anonymous.
Link: https://lkml.kernel.org/r/20230309223711.823547-3-peterx@redhat.com Signed-off-by: Peter Xu <peterx@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Axel Rasmussen <axelrasmussen@google.com> Cc: David Hildenbrand <david@redhat.com> Cc: Mike Rapoport <rppt@linux.vnet.ibm.com> Cc: Muhammad Usama Anjum <usama.anjum@collabora.com> Cc: Nadav Amit <nadav.amit@gmail.com> Cc: Paul Gofman <pgofman@codeweavers.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Peter Xu [Tue, 21 Mar 2023 20:09:26 +0000 (16:09 -0400)]
mm-uffd-uffd_feature_wp_unpopulated-fix
Two comment changes suggested by David, and also a oneliner fix to
khugepaged (to bail out anon thp collapsing when seeing pte markers).
Link: https://lkml.kernel.org/r/ZB2/8jPhD3fpx5U8@x1n Signed-off-by: Peter Xu <peterx@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Axel Rasmussen <axelrasmussen@google.com> Cc: David Hildenbrand <david@redhat.com> Cc: Mike Rapoport <rppt@linux.vnet.ibm.com> Cc: Muhammad Usama Anjum <usama.anjum@collabora.com> Cc: Nadav Amit <nadav.amit@gmail.com> Cc: Paul Gofman <pgofman@codeweavers.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Peter Xu [Thu, 9 Mar 2023 22:37:10 +0000 (17:37 -0500)]
mm/uffd: UFFD_FEATURE_WP_UNPOPULATED
Patch series "mm/uffd: Add feature bit UFFD_FEATURE_WP_UNPOPULATED", v4.
The new feature bit makes anonymous memory acts the same as file memory on
userfaultfd-wp in that it'll also wr-protect none ptes.
It can be useful in two cases:
(1) Uffd-wp app that needs to wr-protect none ptes like QEMU snapshot,
so pre-fault can be replaced by enabling this flag and speed up
protections
(2) It helps to implement async uffd-wp mode that Muhammad is working on [1]
It's debatable whether this is the most ideal solution because with the
new feature bit set, wr-protect none pte needs to pre-populate the
pgtables to the last level (PAGE_SIZE). But it seems fine so far to
service either purpose above, so we can leave optimizations for later.
The series brings pte markers to anonymous memory too. There's some
change in the common mm code path in the 1st patch, great to have some eye
looking at it, but hopefully they're still relatively straightforward.
This patch (of 2):
This is a new feature that controls how uffd-wp handles none ptes. When
it's set, the kernel will handle anonymous memory the same way as file
memory, by allowing the user to wr-protect unpopulated ptes.
File memories handles none ptes consistently by allowing wr-protecting of
none ptes because of the unawareness of page cache being exist or not.
For anonymous it was not as persistent because we used to assume that we
don't need protections on none ptes or known zero pages.
One use case of such a feature bit was VM live snapshot, where if without
wr-protecting empty ptes the snapshot can contain random rubbish in the
holes of the anonymous memory, which can cause misbehave of the guest when
the guest OS assumes the pages should be all zeros.
QEMU worked it around by pre-populate the section with reads to fill in
zero page entries before starting the whole snapshot process [1].
Recently there's another need raised on using userfaultfd wr-protect for
detecting dirty pages (to replace soft-dirty in some cases) [2]. In that
case if without being able to wr-protect none ptes by default, the dirty
info can get lost, since we cannot treat every none pte to be dirty (the
current design is identify a page dirty based on uffd-wp bit being
cleared).
In general, we want to be able to wr-protect empty ptes too even for
anonymous.
This patch implements UFFD_FEATURE_WP_UNPOPULATED so that it'll make
uffd-wp handling on none ptes being consistent no matter what the memory
type is underneath. It doesn't have any impact on file memories so far
because we already have pte markers taking care of that. So it only
affects anonymous.
The feature bit is by default off, so the old behavior will be maintained.
Sometimes it may be wanted because the wr-protect of none ptes will
contain overheads not only during UFFDIO_WRITEPROTECT (by applying pte
markers to anonymous), but also on creating the pgtables to store the pte
markers. So there's potentially less chance of using thp on the first
fault for a none pmd or larger than a pmd.
The major implementation part is teaching the whole kernel to understand
pte markers even for anonymously mapped ranges, meanwhile allowing the
UFFDIO_WRITEPROTECT ioctl to apply pte markers for anonymous too when the
new feature bit is set.
Note that even if the patch subject starts with mm/uffd, there're a few
small refactors to major mm path of handling anonymous page faults. But
they should be straightforward.
With WP_UNPOPUATED, application like QEMU can avoid pre-read faults all
the memory before wr-protect during taking a live snapshot. Quotting from
Muhammad's test result here [3] based on a simple program [4]:
(1) With huge page disabled
echo madvise > /sys/kernel/mm/transparent_hugepage/enabled
./uffd_wp_perf
Test DEFAULT: 4
Test PRE-READ: 1111453 (pre-fault 1101011)
Test MADVISE: 278276 (pre-fault 266378)
Test WP-UNPOPULATE: 11712
(2) With Huge page enabled
echo always > /sys/kernel/mm/transparent_hugepage/enabled
./uffd_wp_perf
Test DEFAULT: 4
Test PRE-READ: 22521 (pre-fault 22348)
Test MADVISE: 4909 (pre-fault 4743)
Test WP-UNPOPULATE: 14448
There'll be a great perf boost for no-thp case, while for thp enabled with
extreme case of all-thp-zero WP_UNPOPULATED can be slower than MADVISE,
but that's low possibility in reality, also the overhead was not reduced
but postponed until a follow up write on any huge zero thp, so potentially
it is faster by making the follow up writes slower.
Link: https://lkml.kernel.org/r/20230309223711.823547-1-peterx@redhat.com Link: https://lkml.kernel.org/r/20230309223711.823547-2-peterx@redhat.com Signed-off-by: Peter Xu <peterx@redhat.com> Acked-by: David Hildenbrand <david@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Axel Rasmussen <axelrasmussen@google.com> Cc: Mike Rapoport <rppt@linux.vnet.ibm.com> Cc: Muhammad Usama Anjum <usama.anjum@collabora.com> Cc: Nadav Amit <nadav.amit@gmail.com> Cc: Paul Gofman <pgofman@codeweavers.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Stefan Roesch [Tue, 14 Mar 2023 20:45:57 +0000 (13:45 -0700)]
docs/mm: extend ksm doc
This adds a description of the new prctl interface for KSM and also adds a
general section on security concerns.
Link: https://lkml.kernel.org/r/20230314204557.3863923-1-shr@devkernel.io Signed-off-by: Stefan Roesch <shr@devkernel.io> Cc: David Hildenbrand <david@redhat.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Rik van Riel <riel@surriel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Stefan Roesch [Fri, 10 Mar 2023 18:28:50 +0000 (10:28 -0800)]
mm: add new KSM process and sysfs knobs
This adds the general_profit KSM sysfs knob and the process profit metric
and process merge type knobs to ksm_stat.
1) split off pages_volatile function
This splits off the pages_volatile function. The next patch will
use this function.
2) expose general_profit metric
The documentation mentions a general profit metric, however this
metric is not calculated. In addition the formula depends on the size
of internal structures, which makes it more difficult for an
administrator to make the calculation. Adding the metric for a better
user experience.
3) document general_profit sysfs knob
4) calculate ksm process profit metric
The ksm documentation mentions the process profit metric and how to
calculate it. This adds the calculation of the metric.
5) add ksm_merge_type() function
This adds the ksm_merge_type function. The function returns the
merge type for the process. For madvise it returns "madvise", for
prctl it returns "process" and otherwise it returns "none".
6) mm: expose ksm process profit metric and merge type in ksm_stat
This exposes the ksm process profit metric in /proc/<pid>/ksm_stat.
The name of the value is ksm_merge_type. The documentation mentions
the formula for the ksm process profit metric, however it does not
calculate it. In addition the formula depends on the size of internal
structures. So it makes sense to expose it.
Stefan Roesch [Fri, 10 Mar 2023 18:28:49 +0000 (10:28 -0800)]
mm: add new api to enable ksm per process
Patch series "mm: process/cgroup ksm support", v4.
So far KSM can only be enabled by calling madvise for memory regions. To
be able to use KSM for more workloads, KSM needs to have the ability to be
enabled / disabled at the process / cgroup level.
Use case 1:
The madvise call is not available in the programming language. An
example for this are programs with forked workloads using a garbage
collected language without pointers. In such a language madvise cannot
be made available.
In addition the addresses of objects get moved around as they are
garbage collected. KSM sharing needs to be enabled "from the outside"
for these type of workloads.
Use case 2:
The same interpreter can also be used for workloads where KSM brings
no benefit or even has overhead. We'd like to be able to enable KSM on
a workload by workload basis.
Use case 3:
With the madvise call sharing opportunities are only enabled for the
current process: it is a workload-local decision. A considerable number
of sharing opportuniites may exist across multiple workloads or jobs.
Only a higler level entity like a job scheduler or container can know
for certain if its running one or more instances of a job. That job
scheduler however doesn't have the necessary internal worklaod knowledge
to make targeted madvise calls.
Security concerns:
In previous discussions security concerns have been brought up. The
problem is that an individual workload does not have the knowledge about
what else is running on a machine. Therefore it has to be very
conservative in what memory areas can be shared or not. However, if the
system is dedicated to running multiple jobs within the same security
domain, its the job scheduler that has the knowledge that sharing can be
safely enabled and is even desirable.
Performance:
Experiments with using UKSM have shown a capacity increase of around
20%.
1. New options for prctl system command
This patch series adds two new options to the prctl system call.
The first one allows to enable KSM at the process level and the second
one to query the setting.
The setting will be inherited by child processes.
With the above setting, KSM can be enabled for the seed process of a
cgroup and all processes in the cgroup will inherit the setting.
2. Changes to KSM processing
When KSM is enabled at the process level, the KSM code will iterate
over all the VMA's and enable KSM for the eligible VMA's.
When forking a process that has KSM enabled, the setting will be
inherited by the new child process.
In addition when KSM is disabled for a process, KSM will be disabled
for the VMA's where KSM has been enabled.
3. Add general_profit metric
The general_profit metric of KSM is specified in the documentation,
but not calculated. This adds the general profit metric to
/sys/kernel/debug/mm/ksm.
4. Add more metrics to ksm_stat
This adds the process profit and ksm type metric to
/proc/<pid>/ksm_stat.
5. Add more tests to ksm_tests
This adds an option to specify the merge type to the ksm_tests.
This allows to test madvise and prctl KSM. It also adds a new option
to query if prctl KSM has been enabled. It adds a fork test to verify
that the KSM process setting is inherited by client processes.
An update to the prctl(2) manpage has been proposed at [1].
This patch (of 3):
This adds a new prctl to API to enable and disable KSM on a per process
basis instead of only at the VMA basis (with madvise).
1) Introduce new MMF_VM_MERGE_ANY flag
This introduces the new flag MMF_VM_MERGE_ANY flag. When this flag
is set, kernel samepage merging (ksm) gets enabled for all vma's of a
process.
2) add flag to __ksm_enter
This change adds the flag parameter to __ksm_enter. This allows to
distinguish if ksm was called by prctl or madvise.
3) add flag to __ksm_exit call
This adds the flag parameter to the __ksm_exit() call. This allows
to distinguish if this call is for an prctl or madvise invocation.
4) invoke madvise for all vmas in scan_get_next_rmap_item
If the new flag MMF_VM_MERGE_ANY has been set for a process, iterate
over all the vmas and enable ksm if possible. For the vmas that can be
ksm enabled this is only done once.
5) support disabling of ksm for a process
This adds the ability to disable ksm for a process if ksm has been
enabled for the process.
6) add new prctl option to get and set ksm for a process
This adds two new options to the prctl system call
- enable ksm for all vmas of a process (if the vmas support it).
- query if ksm has been enabled for a process.
Andrey Konovalov [Fri, 10 Mar 2023 23:43:33 +0000 (00:43 +0100)]
kasan: suppress recursive reports for HW_TAGS
KASAN suppresses reports for bad accesses done by the KASAN reporting
code. The reporting code might access poisoned memory for reporting
purposes.
Software KASAN modes do this by suppressing reports during reporting via
current->kasan_depth, the same way they suppress reports during accesses
to poisoned slab metadata.
Hardware Tag-Based KASAN does not use current->kasan_depth, and instead
resets pointer tags for accesses to poisoned memory done by the reporting
code.
Despite that, a recursive report can still happen:
1. On hardware with faulty MTE support. This was observed by Weizhao
Ouyang on a faulty hardware that caused memory tags to randomly change
from time to time.
2. Theoretically, due to a previous MTE-undetected memory corruption.
A recursive report can happen via:
1. Accessing a pointer with a non-reset tag in the reporting code, e.g.
slab->slab_cache, which is what Weizhao Ouyang observed.
2. Theoretically, via external non-annotated routines, e.g. stackdepot.
To resolve this issue, resetting tags for all of the pointers in the
reporting code and all the used external routines would be impractical.
Instead, disable tag checking done by the CPU for the duration of KASAN
reporting for Hardware Tag-Based KASAN.
Without this fix, Hardware Tag-Based KASAN reporting code might deadlock.
Andrey Konovalov [Fri, 10 Mar 2023 23:43:29 +0000 (00:43 +0100)]
kasan: drop empty tagging-related defines
mm/kasan/kasan.h provides a number of empty defines for a few
arch-specific tagging-related routines, in case the architecture code
didn't define them.
The original idea was to simplify integration in case another architecture
starts supporting memory tagging. However, right now, if any of those
routines are not provided by an architecture, Hardware Tag-Based KASAN
won't work.
Drop the empty defines, as it would be better to get compiler errors
rather than runtime crashes when adding support for a new architecture.
Also drop empty hw_enable_tagging_sync/async/asymm defines for
!CONFIG_KASAN_HW_TAGS case, as those are only used in mm/kasan/hw_tags.c.
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