Re: [PATCH v2 7/7] mm: shmem: add mTHP counters for anonymous shmem

[Baolin Wang]

On 2024/5/14 22:49, Lance Yang wrote:
> Hi Baolin,
>
> On Mon, May 13, 2024 at 1:08 PM Baolin Wang
> <baolin.wang@xxxxxxxxxxxxxxxxx> wrote:
> > Add mTHP counters for anonymous shmem.
> >
> > Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> > ---
> >   include/linux/huge_mm.h |  3 +++
> >   mm/huge_memory.c        |  6 ++++++
> >   mm/shmem.c              | 18 +++++++++++++++---
> >   3 files changed, 24 insertions(+), 3 deletions(-)
> >
> > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> > index b5339210268d..e162498fef82 100644
> > --- a/include/linux/huge_mm.h
> > +++ b/include/linux/huge_mm.h
> > @@ -281,6 +281,9 @@ enum mthp_stat_item {
> >          MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE,
> >          MTHP_STAT_ANON_SWPOUT,
> >          MTHP_STAT_ANON_SWPOUT_FALLBACK,
> > +       MTHP_STAT_FILE_ALLOC,
> > +       MTHP_STAT_FILE_FALLBACK,
> > +       MTHP_STAT_FILE_FALLBACK_CHARGE,
> >          __MTHP_STAT_COUNT
> >   };
> >
> > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> > index d3080a8843f2..fcda6ae604f6 100644
> > --- a/mm/huge_memory.c
> > +++ b/mm/huge_memory.c
> > @@ -555,6 +555,9 @@ DEFINE_MTHP_STAT_ATTR(anon_fault_fallback, MTHP_STAT_ANON_FAULT_FALLBACK);
> >   DEFINE_MTHP_STAT_ATTR(anon_fault_fallback_charge, MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE);
> >   DEFINE_MTHP_STAT_ATTR(anon_swpout, MTHP_STAT_ANON_SWPOUT);
> >   DEFINE_MTHP_STAT_ATTR(anon_swpout_fallback, MTHP_STAT_ANON_SWPOUT_FALLBACK);
> > +DEFINE_MTHP_STAT_ATTR(file_alloc, MTHP_STAT_FILE_ALLOC);
> > +DEFINE_MTHP_STAT_ATTR(file_fallback, MTHP_STAT_FILE_FALLBACK);
> > +DEFINE_MTHP_STAT_ATTR(file_fallback_charge, MTHP_STAT_FILE_FALLBACK_CHARGE);
> >
> >   static struct attribute *stats_attrs[] = {
> >          &anon_fault_alloc_attr.attr,
> > @@ -562,6 +565,9 @@ static struct attribute *stats_attrs[] = {
> >          &anon_fault_fallback_charge_attr.attr,
> >          &anon_swpout_attr.attr,
> >          &anon_swpout_fallback_attr.attr,
> > +       &file_alloc_attr.attr,
> > +       &file_fallback_attr.attr,
> > +       &file_fallback_charge_attr.attr,
> >          NULL,
> >   };
> >
> > diff --git a/mm/shmem.c b/mm/shmem.c
> > index 8b020ff09c72..fd2cb2e73a21 100644
> > --- a/mm/shmem.c
> > +++ b/mm/shmem.c
> > @@ -1786,6 +1786,9 @@ static struct folio *shmem_alloc_and_add_folio(struct vm_fault *vmf,
> >
> >                          if (pages == HPAGE_PMD_NR)
> >                                  count_vm_event(THP_FILE_FALLBACK);
> > +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> > +                       count_mthp_stat(order, MTHP_STAT_FILE_FALLBACK);
> > +#endif
>
> Seems like we don't need these conditional compilation directives here.
>
> The THP_FILE_FALLBACK above will result in a compilation error if
> CONFIG_TRANSPARENT_HUGEPAGE is not defined. So we don't
> worry about that :)
>
> See THP_FILE_FALLBACK in include/linux/vm_event_item.h.
>
> >                          order = next_order(&suitable_orders, order);
> >                  }
> >          } else {
> > @@ -1805,9 +1808,15 @@ static struct folio *shmem_alloc_and_add_folio(struct vm_fault *vmf,
> >                  if (xa_find(&mapping->i_pages, &index,
> >                                  index + pages - 1, XA_PRESENT)) {
> >                          error = -EEXIST;
> > -               } else if (pages == HPAGE_PMD_NR) {
> > -                       count_vm_event(THP_FILE_FALLBACK);
> > -                       count_vm_event(THP_FILE_FALLBACK_CHARGE);
> > +               } else if (pages > 1) {
> > +                       if (pages == HPAGE_PMD_NR) {
> > +                               count_vm_event(THP_FILE_FALLBACK);
> > +                               count_vm_event(THP_FILE_FALLBACK_CHARGE);
> > +                       }
> > +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> > +                       count_mthp_stat(folio_order(folio), MTHP_STAT_FILE_FALLBACK);
> > +                       count_mthp_stat(folio_order(folio), MTHP_STAT_FILE_FALLBACK_CHARGE);
> > +#endif
>
> As above.
>
> >                  }
> >                  goto unlock;
> >          }
> > @@ -2178,6 +2187,9 @@ static int shmem_get_folio_gfp(struct inode *inode, pgoff_t index,
> >                  if (!IS_ERR(folio)) {
> >                          if (folio_test_pmd_mappable(folio))
> >                                  count_vm_event(THP_FILE_ALLOC);
> > +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> > +                       count_mthp_stat(folio_order(folio), MTHP_STAT_FILE_ALLOC);
> > +#endif
>
> As above.
>
> Perhaps we need to define MTHP_STAT_FILE_ALLOC and friends
> using a same way as THP_FILE_ALLOC, set as '{ BUILD_BUG(); 0; }'
> If CONFIG_TRANSPARENT_HUGEPAGE is not defined.
>
> Likely:
>
> #ifndef CONFIG_TRANSPARENT_HUGEPAGE
> #define MTHP_STAT_FILE_ALLOC ({ BUILD_BUG(); 0; })
> ...
> #endif

This is not enough, and we should also define a dummy function for 
count_mthp_stat() when CONFIG_TRANSPARENT_HUGEPAGE is not enabled. I was 
also hesitant about doing this before, but adding macro controls seems 
relatively simple:)

Thanks for reviewing.