Re: [PATCH v2 1/2] mm: add per-order mTHP split counters

[Lance Yang <ioworker0@gmail.com>]

Hi Ryan,

On Mon, Jul 1, 2024 at 4:18 PM Ryan Roberts <ryan.roberts@arm.com> wrote:
>
> On 28/06/2024 14:07, Lance Yang wrote:
> > Currently, the split counters in THP statistics no longer include
> > PTE-mapped mTHP. Therefore, we propose introducing per-order mTHP split
> > counters to monitor the frequency of mTHP splits. This will help developers
> > better analyze and optimize system performance.
> >
> > /sys/kernel/mm/transparent_hugepage/hugepages-<size>/stats
> >         split
> >         split_failed
> >         split_deferred
> >
> > Signed-off-by: Mingzhe Yang <mingzhe.yang@ly.com>
> > Signed-off-by: Lance Yang <ioworker0@gmail.com>
>
> LGTM!
>
> Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>

Thanks for taking time to review!
Lance

>
> > ---
> >  include/linux/huge_mm.h |  3 +++
> >  mm/huge_memory.c        | 19 ++++++++++++++-----
> >  2 files changed, 17 insertions(+), 5 deletions(-)
> >
> > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> > index 212cca384d7e..cee3c5da8f0e 100644
> > --- a/include/linux/huge_mm.h
> > +++ b/include/linux/huge_mm.h
> > @@ -284,6 +284,9 @@ enum mthp_stat_item {
> >       MTHP_STAT_FILE_ALLOC,
> >       MTHP_STAT_FILE_FALLBACK,
> >       MTHP_STAT_FILE_FALLBACK_CHARGE,
> > +     MTHP_STAT_SPLIT,
> > +     MTHP_STAT_SPLIT_FAILED,
> > +     MTHP_STAT_SPLIT_DEFERRED,
> >       __MTHP_STAT_COUNT
> >  };
> >
> > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> > index c7ce28f6b7f3..a633206375af 100644
> > --- a/mm/huge_memory.c
> > +++ b/mm/huge_memory.c
> > @@ -559,6 +559,9 @@ DEFINE_MTHP_STAT_ATTR(swpout_fallback, MTHP_STAT_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);
> > +DEFINE_MTHP_STAT_ATTR(split, MTHP_STAT_SPLIT);
> > +DEFINE_MTHP_STAT_ATTR(split_failed, MTHP_STAT_SPLIT_FAILED);
> > +DEFINE_MTHP_STAT_ATTR(split_deferred, MTHP_STAT_SPLIT_DEFERRED);
> >
> >  static struct attribute *stats_attrs[] = {
> >       &anon_fault_alloc_attr.attr,
> > @@ -569,6 +572,9 @@ static struct attribute *stats_attrs[] = {
> >       &file_alloc_attr.attr,
> >       &file_fallback_attr.attr,
> >       &file_fallback_charge_attr.attr,
> > +     &split_attr.attr,
> > +     &split_failed_attr.attr,
> > +     &split_deferred_attr.attr,
> >       NULL,
> >  };
> >
> > @@ -3068,7 +3074,7 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
> >       XA_STATE_ORDER(xas, &folio->mapping->i_pages, folio->index, new_order);
> >       struct anon_vma *anon_vma = NULL;
> >       struct address_space *mapping = NULL;
> > -     bool is_thp = folio_test_pmd_mappable(folio);
> > +     int order = folio_order(folio);
> >       int extra_pins, ret;
> >       pgoff_t end;
> >       bool is_hzp;
> > @@ -3076,7 +3082,7 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
> >       VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
> >       VM_BUG_ON_FOLIO(!folio_test_large(folio), folio);
> >
> > -     if (new_order >= folio_order(folio))
> > +     if (new_order >= order)
> >               return -EINVAL;
> >
> >       if (folio_test_anon(folio)) {
> > @@ -3253,8 +3259,9 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
> >               i_mmap_unlock_read(mapping);
> >  out:
> >       xas_destroy(&xas);
> > -     if (is_thp)
> > +     if (order >= HPAGE_PMD_ORDER)
> >               count_vm_event(!ret ? THP_SPLIT_PAGE : THP_SPLIT_PAGE_FAILED);
> > +     count_mthp_stat(order, !ret ? MTHP_STAT_SPLIT : MTHP_STAT_SPLIT_FAILED);
> >       return ret;
> >  }
> >
> > @@ -3278,13 +3285,14 @@ void deferred_split_folio(struct folio *folio)
> >  #ifdef CONFIG_MEMCG
> >       struct mem_cgroup *memcg = folio_memcg(folio);
> >  #endif
> > +     int order = folio_order(folio);
> >       unsigned long flags;
> >
> >       /*
> >        * Order 1 folios have no space for a deferred list, but we also
> >        * won't waste much memory by not adding them to the deferred list.
> >        */
> > -     if (folio_order(folio) <= 1)
> > +     if (order <= 1)
> >               return;
> >
> >       /*
> > @@ -3305,8 +3313,9 @@ void deferred_split_folio(struct folio *folio)
> >
> >       spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
> >       if (list_empty(&folio->_deferred_list)) {
> > -             if (folio_test_pmd_mappable(folio))
> > +             if (order >= HPAGE_PMD_ORDER)
> >                       count_vm_event(THP_DEFERRED_SPLIT_PAGE);
> > +             count_mthp_stat(order, MTHP_STAT_SPLIT_DEFERRED);
> >               list_add_tail(&folio->_deferred_list, &ds_queue->split_queue);
> >               ds_queue->split_queue_len++;
> >  #ifdef CONFIG_MEMCG
>