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mm: thp: fix false negative of shmem vma's THP eligibility
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Commit 7635d9c ("mm, thp, proc: report THP eligibility for each
vma") introduced THPeligible bit for processes' smaps.  But, when
checking the eligibility for shmem vma, __transparent_hugepage_enabled()
is called to override the result from shmem_huge_enabled().  It may
result in the anonymous vma's THP flag override shmem's.  For example,
running a simple test which create THP for shmem, but with anonymous THP
disabled, when reading the process's smaps, it may show:

  7fc92ec00000-7fc92f000000 rw-s 00000000 00:14 27764 /dev/shm/test
  Size:               4096 kB
  ...
  [snip]
  ...
  ShmemPmdMapped:     4096 kB
  ...
  [snip]
  ...
  THPeligible:    0

And, /proc/meminfo does show THP allocated and PMD mapped too:

  ShmemHugePages:     4096 kB
  ShmemPmdMapped:     4096 kB

This doesn't make too much sense.  The shmem objects should be treated
separately from anonymous THP.  Calling shmem_huge_enabled() with
checking MMF_DISABLE_THP sounds good enough.  And, we could skip stack
and dax vma check since we already checked if the vma is shmem already.

Also check if vma is suitable for THP by calling
transhuge_vma_suitable().

And minor fix to smaps output format and documentation.

Link: http://lkml.kernel.org/r/[email protected]
Fixes: 7635d9c ("mm, thp, proc: report THP eligibility for each vma")
Signed-off-by: Yang Shi <[email protected]>
Acked-by: Hugh Dickins <[email protected]>
Cc: Kirill A. Shutemov <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
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Yang Shi authored and torvalds committed Jul 19, 2019
1 parent 43675e6 commit c063066
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Showing 4 changed files with 14 additions and 5 deletions.
4 changes: 2 additions & 2 deletions Documentation/filesystems/proc.txt
Original file line number Diff line number Diff line change
Expand Up @@ -486,8 +486,8 @@ replaced by copy-on-write) part of the underlying shmem object out on swap.
"SwapPss" shows proportional swap share of this mapping. Unlike "Swap", this
does not take into account swapped out page of underlying shmem objects.
"Locked" indicates whether the mapping is locked in memory or not.
"THPeligible" indicates whether the mapping is eligible for THP pages - 1 if
true, 0 otherwise.
"THPeligible" indicates whether the mapping is eligible for allocating THP
pages - 1 if true, 0 otherwise. It just shows the current status.

"VmFlags" field deserves a separate description. This member represents the kernel
flags associated with the particular virtual memory area in two letter encoded
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3 changes: 2 additions & 1 deletion fs/proc/task_mmu.c
Original file line number Diff line number Diff line change
Expand Up @@ -832,7 +832,8 @@ static int show_smap(struct seq_file *m, void *v)

__show_smap(m, &mss, false);

seq_printf(m, "THPeligible: %d\n", transparent_hugepage_enabled(vma));
seq_printf(m, "THPeligible: %d\n",
transparent_hugepage_enabled(vma));

if (arch_pkeys_enabled())
seq_printf(m, "ProtectionKey: %8u\n", vma_pkey(vma));
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9 changes: 7 additions & 2 deletions mm/huge_memory.c
Original file line number Diff line number Diff line change
Expand Up @@ -63,10 +63,15 @@ struct page *huge_zero_page __read_mostly;

bool transparent_hugepage_enabled(struct vm_area_struct *vma)
{
/* The addr is used to check if the vma size fits */
unsigned long addr = (vma->vm_end & HPAGE_PMD_MASK) - HPAGE_PMD_SIZE;

if (!transhuge_vma_suitable(vma, addr))
return false;
if (vma_is_anonymous(vma))
return __transparent_hugepage_enabled(vma);
if (vma_is_shmem(vma) && shmem_huge_enabled(vma))
return __transparent_hugepage_enabled(vma);
if (vma_is_shmem(vma))
return shmem_huge_enabled(vma);

return false;
}
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3 changes: 3 additions & 0 deletions mm/shmem.c
Original file line number Diff line number Diff line change
Expand Up @@ -3874,6 +3874,9 @@ bool shmem_huge_enabled(struct vm_area_struct *vma)
loff_t i_size;
pgoff_t off;

if ((vma->vm_flags & VM_NOHUGEPAGE) ||
test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags))
return false;
if (shmem_huge == SHMEM_HUGE_FORCE)
return true;
if (shmem_huge == SHMEM_HUGE_DENY)
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