On Thu, 13 Jun 2019, Yang Shi wrote:
> The commit 7635d9cbe832 ("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.
>
> Fixes: 7635d9cbe832 ("mm, thp, proc: report THP eligibility for each vma")
> Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Thanks,
Acked-by: Hugh Dickins <hughd@xxxxxxxxxx>
> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: Vlastimil Babka <vbabka@xxxxxxx>
> Cc: David Rientjes <rientjes@xxxxxxxxxx>
> Signed-off-by: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
> ---
> Documentation/filesystems/proc.txt | 4 ++--
> fs/proc/task_mmu.c | 3 ++-
> mm/huge_memory.c | 9 +++++++--
> mm/shmem.c | 3 +++
> 4 files changed, 14 insertions(+), 5 deletions(-)
>
> diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
> index 66cad5c..b0ded06 100644
> --- a/Documentation/filesystems/proc.txt
> +++ b/Documentation/filesystems/proc.txt
> @@ -477,8 +477,8 @@ 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
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 01d4eb0..6a13882 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -796,7 +796,8 @@ static int show_smap(struct seq_file *m, void *v)
>
> __show_smap(m, &mss);
>
> - 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));
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 4bc2552..36f0225 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -65,10 +65,15 @@
>
> 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;
> }
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 1bb3b8d..a807712 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -3872,6 +3872,9 @@ 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)
> --
> 1.8.3.1
