mm: thp: fix false negative of shmem vma's THP eligibility (c0630669) · Commits · 戴 / test

Commit ("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/1560401041-32207-3-git-send-email-yang.shi@linux.alibaba.com Fixes: ("mm, thp, proc: report THP eligibility for each vma") Signed-off-by:

Yang Shi <yang.shi@linux.alibaba.com> Acked-by:

Hugh Dickins <hughd@google.com> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: David Rientjes <rientjes@google.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

Documentation/filesystems/proc.txt

+2 −2

Original line number	Diff line number	Diff line
		@@ -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

fs/proc/task_mmu.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -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));

mm/huge_memory.c

+7 −2

Original line number	Diff line number	Diff line
		@@ -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;
		}

mm/shmem.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -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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