mm: mmap: register suitable readonly file vmas for khugepaged

The readonly FS THP relies on khugepaged to collapse THP for suitable
vmas.  But it is kind of "random luck" for khugepaged to see the readonly
FS vmas
(https://lore.kernel.org/linux-mm/00f195d4-d039-3cf2-d3a1-a2c88de397a0@suse.cz/)
since currently the vmas are registered to khugepaged when:

  - Anon huge pmd page fault
  - VMA merge
  - MADV_HUGEPAGE
  - Shmem mmap

If the above conditions are not met, even though khugepaged is enabled it
won't see readonly FS vmas at all.  MADV_HUGEPAGE could be specified
explicitly to tell khugepaged to collapse this area, but when khugepaged
mode is "always" it should scan suitable vmas as long as VM_NOHUGEPAGE is
not set.

So make sure readonly FS vmas are registered to khugepaged to make the
behavior more consistent.

Registering suitable vmas in common mmap path, that could cover both
readonly FS vmas and shmem vmas, so removed the khugepaged calls in
shmem.c.

Still need to keep the khugepaged call in vma_merge() since vma_merge() is
called in a lot of places, for example, madvise, mprotect, etc.

Link: https://lkml.kernel.org/r/20220404200250.321455-9-shy828301@gmail.com
Signed-off-by: Yang Shi <shy828301@gmail.com>
Reported-by: Vlastimil Babka <vbabka@suse.cz>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Song Liu <song@kernel.org>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/mmap.c b/mm/mmap.c
index e3695eb34ad4071d2026d1590f1494de3474f9bb..f172f3aba90ff4bb8e5ae5313b3834cd87768efb 100644 (file)
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2682,6 +2682,12 @@ cannot_expand:
                i_mmap_unlock_write(vma->vm_file->f_mapping);
        }
 
+       /*
+        * vma_merge() calls khugepaged_enter_vma() either, the below
+        * call covers the non-merge case.
+        */
+       khugepaged_enter_vma(vma, vma->vm_flags);
+
        /* Once vma denies write, undo our temporary denial count */
 unmap_writable:
        if (file && vm_flags & VM_SHARED)

diff --git a/mm/shmem.c b/mm/shmem.c
index 6163ef5acbcd95c152aeccfa88209c1cca3f9abd..4a966d2de2ad81e179c06e8d2d2e4a74c7db3a4b 100644 (file)
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -34,7 +34,6 @@
 #include <linux/export.h>
 #include <linux/swap.h>
 #include <linux/uio.h>
-#include <linux/khugepaged.h>
 #include <linux/hugetlb.h>
 #include <linux/fs_parser.h>
 #include <linux/swapfile.h>
@@ -2240,7 +2239,6 @@ static int shmem_mmap(struct file *file, struct vm_area_struct *vma)
 
        file_accessed(file);
        vma->vm_ops = &shmem_vm_ops;
-       khugepaged_enter_vma(vma, vma->vm_flags);
        return 0;
 }
 
@@ -4139,8 +4137,6 @@ int shmem_zero_setup(struct vm_area_struct *vma)
        vma->vm_file = file;
        vma->vm_ops = &shmem_vm_ops;
 
-       khugepaged_enter_vma(vma, vma->vm_flags);
-
        return 0;
 }