enabled.
The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG
-bits on both physical and virtual pages associated with a process.
+bits on both physical and virtual pages associated with a process, and the
+soft-dirty bit on pte (see Documentation/vm/soft-dirty.txt for details).
To clear the bits for all the pages associated with the process
> echo 1 > /proc/PID/clear_refs
To clear the bits for the file mapped pages associated with the process
> echo 3 > /proc/PID/clear_refs
+
+To clear the soft-dirty bit
+ > echo 4 > /proc/PID/clear_refs
+
Any other value written to /proc/PID/clear_refs will have no effect.
The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags
--- /dev/null
+ SOFT-DIRTY PTEs
+
+ The soft-dirty is a bit on a PTE which helps to track which pages a task
+writes to. In order to do this tracking one should
+
+ 1. Clear soft-dirty bits from the task's PTEs.
+
+ This is done by writing "4" into the /proc/PID/clear_refs file of the
+ task in question.
+
+ 2. Wait some time.
+
+ 3. Read soft-dirty bits from the PTEs.
+
+ This is done by reading from the /proc/PID/pagemap. The bit 55 of the
+ 64-bit qword is the soft-dirty one. If set, the respective PTE was
+ written to since step 1.
+
+
+ Internally, to do this tracking, the writable bit is cleared from PTEs
+when the soft-dirty bit is cleared. So, after this, when the task tries to
+modify a page at some virtual address the #PF occurs and the kernel sets
+the soft-dirty bit on the respective PTE.
+
+ Note, that although all the task's address space is marked as r/o after the
+soft-dirty bits clear, the #PF-s that occur after that are processed fast.
+This is so, since the pages are still mapped to physical memory, and thus all
+the kernel does is finds this fact out and puts both writable and soft-dirty
+bits on the PTE.
+
+
+ This feature is actively used by the checkpoint-restore project. You
+can find more details about it on http://criu.org
+
+
+-- Pavel Emelyanov, Apr 9, 2013
config HAVE_ARCH_TRANSPARENT_HUGEPAGE
bool
+config HAVE_ARCH_SOFT_DIRTY
+ bool
+
config HAVE_MOD_ARCH_SPECIFIC
bool
help
select HAVE_ARCH_SECCOMP_FILTER
select BUILDTIME_EXTABLE_SORT
select GENERIC_CMOS_UPDATE
+ select HAVE_ARCH_SOFT_DIRTY
select CLOCKSOURCE_WATCHDOG
select GENERIC_CLOCKEVENTS
select ARCH_CLOCKSOURCE_DATA if X86_64
static inline pte_t pte_mkdirty(pte_t pte)
{
- return pte_set_flags(pte, _PAGE_DIRTY);
+ return pte_set_flags(pte, _PAGE_DIRTY | _PAGE_SOFT_DIRTY);
}
static inline pte_t pte_mkyoung(pte_t pte)
static inline pmd_t pmd_mkdirty(pmd_t pmd)
{
- return pmd_set_flags(pmd, _PAGE_DIRTY);
+ return pmd_set_flags(pmd, _PAGE_DIRTY | _PAGE_SOFT_DIRTY);
}
static inline pmd_t pmd_mkhuge(pmd_t pmd)
return pmd_clear_flags(pmd, _PAGE_PRESENT);
}
+static inline int pte_soft_dirty(pte_t pte)
+{
+ return pte_flags(pte) & _PAGE_SOFT_DIRTY;
+}
+
+static inline int pmd_soft_dirty(pmd_t pmd)
+{
+ return pmd_flags(pmd) & _PAGE_SOFT_DIRTY;
+}
+
+static inline pte_t pte_mksoft_dirty(pte_t pte)
+{
+ return pte_set_flags(pte, _PAGE_SOFT_DIRTY);
+}
+
+static inline pmd_t pmd_mksoft_dirty(pmd_t pmd)
+{
+ return pmd_set_flags(pmd, _PAGE_SOFT_DIRTY);
+}
+
/*
* Mask out unsupported bits in a present pgprot. Non-present pgprots
* can use those bits for other purposes, so leave them be.
#define _PAGE_HIDDEN (_AT(pteval_t, 0))
#endif
+/*
+ * The same hidden bit is used by kmemcheck, but since kmemcheck
+ * works on kernel pages while soft-dirty engine on user space,
+ * they do not conflict with each other.
+ */
+
+#ifdef CONFIG_MEM_SOFT_DIRTY
+#define _PAGE_SOFT_DIRTY (_AT(pteval_t, 1) << _PAGE_BIT_HIDDEN)
+#else
+#define _PAGE_SOFT_DIRTY (_AT(pteval_t, 0))
+#endif
+
#if defined(CONFIG_X86_64) || defined(CONFIG_X86_PAE)
#define _PAGE_NX (_AT(pteval_t, 1) << _PAGE_BIT_NX)
#else
#include <linux/rmap.h>
#include <linux/swap.h>
#include <linux/swapops.h>
+#include <linux/mmu_notifier.h>
#include <asm/elf.h>
#include <asm/uaccess.h>
CLEAR_REFS_ALL = 1,
CLEAR_REFS_ANON,
CLEAR_REFS_MAPPED,
+ CLEAR_REFS_SOFT_DIRTY,
CLEAR_REFS_LAST,
};
struct clear_refs_private {
struct vm_area_struct *vma;
+ enum clear_refs_types type;
};
+static inline void clear_soft_dirty(struct vm_area_struct *vma,
+ unsigned long addr, pte_t *pte)
+{
+#ifdef CONFIG_MEM_SOFT_DIRTY
+ /*
+ * The soft-dirty tracker uses #PF-s to catch writes
+ * to pages, so write-protect the pte as well. See the
+ * Documentation/vm/soft-dirty.txt for full description
+ * of how soft-dirty works.
+ */
+ pte_t ptent = *pte;
+ ptent = pte_wrprotect(ptent);
+ ptent = pte_clear_flags(ptent, _PAGE_SOFT_DIRTY);
+ set_pte_at(vma->vm_mm, addr, pte, ptent);
+#endif
+}
+
static int clear_refs_pte_range(pmd_t *pmd, unsigned long addr,
unsigned long end, struct mm_walk *walk)
{
if (!pte_present(ptent))
continue;
+ if (cp->type == CLEAR_REFS_SOFT_DIRTY) {
+ clear_soft_dirty(vma, addr, pte);
+ continue;
+ }
+
page = vm_normal_page(vma, addr, ptent);
if (!page)
continue;
mm = get_task_mm(task);
if (mm) {
struct clear_refs_private cp = {
+ .type = type,
};
struct mm_walk clear_refs_walk = {
.pmd_entry = clear_refs_pte_range,
.private = &cp,
};
down_read(&mm->mmap_sem);
+ if (type == CLEAR_REFS_SOFT_DIRTY)
+ mmu_notifier_invalidate_range_start(mm, 0, -1);
for (vma = mm->mmap; vma; vma = vma->vm_next) {
cp.vma = vma;
if (is_vm_hugetlb_page(vma))
walk_page_range(vma->vm_start, vma->vm_end,
&clear_refs_walk);
}
+ if (type == CLEAR_REFS_SOFT_DIRTY)
+ mmu_notifier_invalidate_range_end(mm, 0, -1);
flush_tlb_mm(mm);
up_read(&mm->mmap_sem);
mmput(mm);
/* in "new" pagemap pshift bits are occupied with more status bits */
#define PM_STATUS2(v2, x) (__PM_PSHIFT(v2 ? x : PAGE_SHIFT))
+#define __PM_SOFT_DIRTY (1LL)
#define PM_PRESENT PM_STATUS(4LL)
#define PM_SWAP PM_STATUS(2LL)
#define PM_FILE PM_STATUS(1LL)
{
u64 frame, flags;
struct page *page = NULL;
+ int flags2 = 0;
if (pte_present(pte)) {
frame = pte_pfn(pte);
if (page && !PageAnon(page))
flags |= PM_FILE;
+ if (pte_soft_dirty(pte))
+ flags2 |= __PM_SOFT_DIRTY;
- *pme = make_pme(PM_PFRAME(frame) | PM_STATUS2(pm->v2, 0) | flags);
+ *pme = make_pme(PM_PFRAME(frame) | PM_STATUS2(pm->v2, flags2) | flags);
}
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
static void thp_pmd_to_pagemap_entry(pagemap_entry_t *pme, struct pagemapread *pm,
- pmd_t pmd, int offset)
+ pmd_t pmd, int offset, int pmd_flags2)
{
/*
* Currently pmd for thp is always present because thp can not be
*/
if (pmd_present(pmd))
*pme = make_pme(PM_PFRAME(pmd_pfn(pmd) + offset)
- | PM_STATUS2(pm->v2, 0) | PM_PRESENT);
+ | PM_STATUS2(pm->v2, pmd_flags2) | PM_PRESENT);
else
*pme = make_pme(PM_NOT_PRESENT(pm->v2));
}
#else
static inline void thp_pmd_to_pagemap_entry(pagemap_entry_t *pme, struct pagemapread *pm,
- pmd_t pmd, int offset)
+ pmd_t pmd, int offset, int pmd_flags2)
{
}
#endif
/* find the first VMA at or above 'addr' */
vma = find_vma(walk->mm, addr);
if (vma && pmd_trans_huge_lock(pmd, vma) == 1) {
+ int pmd_flags2;
+
+ pmd_flags2 = (pmd_soft_dirty(*pmd) ? __PM_SOFT_DIRTY : 0);
for (; addr != end; addr += PAGE_SIZE) {
unsigned long offset;
offset = (addr & ~PAGEMAP_WALK_MASK) >>
PAGE_SHIFT;
- thp_pmd_to_pagemap_entry(&pme, pm, *pmd, offset);
+ thp_pmd_to_pagemap_entry(&pme, pm, *pmd, offset, pmd_flags2);
err = add_to_pagemap(addr, &pme, pm);
if (err)
break;
#define arch_start_context_switch(prev) do {} while (0)
#endif
+#ifndef CONFIG_HAVE_ARCH_SOFT_DIRTY
+static inline int pte_soft_dirty(pte_t pte)
+{
+ return 0;
+}
+
+static inline int pmd_soft_dirty(pmd_t pmd)
+{
+ return 0;
+}
+
+static inline pte_t pte_mksoft_dirty(pte_t pte)
+{
+ return pte;
+}
+
+static inline pmd_t pmd_mksoft_dirty(pmd_t pmd)
+{
+ return pmd;
+}
+#endif
+
#ifndef __HAVE_PFNMAP_TRACKING
/*
* Interfaces that can be used by architecture code to keep track of
and swap data is stored as normal on the matching swap device.
If unsure, say Y to enable frontswap.
+
+config MEM_SOFT_DIRTY
+ bool "Track memory changes"
+ depends on CHECKPOINT_RESTORE && HAVE_ARCH_SOFT_DIRTY
+ select PROC_PAGE_MONITOR
+ help
+ This option enables memory changes tracking by introducing a
+ soft-dirty bit on pte-s. This bit it set when someone writes
+ into a page just as regular dirty bit, but unlike the latter
+ it can be cleared by hands.
+
+ See Documentation/vm/soft-dirty.txt for more details.
if (ret == 1) {
pmd = pmdp_get_and_clear(mm, old_addr, old_pmd);
VM_BUG_ON(!pmd_none(*new_pmd));
- set_pmd_at(mm, new_addr, new_pmd, pmd);
+ set_pmd_at(mm, new_addr, new_pmd, pmd_mksoft_dirty(pmd));
spin_unlock(&mm->page_table_lock);
}
out:
continue;
pte = ptep_get_and_clear(mm, old_addr, old_pte);
pte = move_pte(pte, new_vma->vm_page_prot, old_addr, new_addr);
- set_pte_at(mm, new_addr, new_pte, pte);
+ set_pte_at(mm, new_addr, new_pte, pte_mksoft_dirty(pte));
}
arch_leave_lazy_mmu_mode();
projects / users / hch / configfs.git / commitdiff