Re: [patch 1/2] mm, shmem: add thp fault alloc and fallback stats

[Yang Shi]

On Tue, Feb 18, 2020 at 6:29 PM David Rientjes <rientjes@xxxxxxxxxx> wrote:
>
> The thp_fault_alloc and thp_fault_fallback vmstats are incremented when a
> hugepage is successfully or unsuccessfully allocated, respectively, during
> a page fault for anonymous memory.
>
> Extend this to shmem as well.  Note that care is taken to increment
> thp_fault_alloc only when the fault succeeds; this is the same behavior as
> anonymous thp.
>
> Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
> ---
>  mm/shmem.c | 23 ++++++++++++++---------
>  1 file changed, 14 insertions(+), 9 deletions(-)
>
> diff --git a/mm/shmem.c b/mm/shmem.c
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -1502,9 +1502,8 @@ static struct page *shmem_alloc_page(gfp_t gfp,
>         return page;
>  }
>
> -static struct page *shmem_alloc_and_acct_page(gfp_t gfp,
> -               struct inode *inode,
> -               pgoff_t index, bool huge)
> +static struct page *shmem_alloc_and_acct_page(gfp_t gfp, struct inode *inode,
> +               pgoff_t index, bool fault, bool huge)
>  {
>         struct shmem_inode_info *info = SHMEM_I(inode);
>         struct page *page;
> @@ -1518,9 +1517,11 @@ static struct page *shmem_alloc_and_acct_page(gfp_t gfp,
>         if (!shmem_inode_acct_block(inode, nr))
>                 goto failed;
>
> -       if (huge)
> +       if (huge) {
>                 page = shmem_alloc_hugepage(gfp, info, index);
> -       else
> +               if (!page && fault)
> +                       count_vm_event(THP_FAULT_FALLBACK);
> +       } else
>                 page = shmem_alloc_page(gfp, info, index);
>         if (page) {
>                 __SetPageLocked(page);
> @@ -1832,11 +1833,10 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
>         }
>
>  alloc_huge:
> -       page = shmem_alloc_and_acct_page(gfp, inode, index, true);
> +       page = shmem_alloc_and_acct_page(gfp, inode, index, vmf, true);
>         if (IS_ERR(page)) {
>  alloc_nohuge:
> -               page = shmem_alloc_and_acct_page(gfp, inode,
> -                                                index, false);
> +               page = shmem_alloc_and_acct_page(gfp, inode, index, vmf, false);
>         }
>         if (IS_ERR(page)) {
>                 int retry = 5;
> @@ -1871,8 +1871,11 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
>
>         error = mem_cgroup_try_charge_delay(page, charge_mm, gfp, &memcg,
>                                             PageTransHuge(page));
> -       if (error)
> +       if (error) {
> +               if (vmf && PageTransHuge(page))
> +                       count_vm_event(THP_FAULT_FALLBACK);
>                 goto unacct;
> +       }
>         error = shmem_add_to_page_cache(page, mapping, hindex,
>                                         NULL, gfp & GFP_RECLAIM_MASK);
>         if (error) {
> @@ -1883,6 +1886,8 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
>         mem_cgroup_commit_charge(page, memcg, false,
>                                  PageTransHuge(page));
>         lru_cache_add_anon(page);
> +       if (vmf && PageTransHuge(page))
> +               count_vm_event(THP_FAULT_ALLOC);

I think shmem THP alloc is accounted to THP_FILE_ALLOC. And it has
been accounted by shmem_add_to_page_cache(). So, it sounds like a
double count.

>
>         spin_lock_irq(&info->lock);
>         info->alloced += compound_nr(page);
>