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

[Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>]

On 2024/7/1 08:02, Barry Song wrote:
> On Sat, Jun 29, 2024 at 1:09 AM Lance Yang <ioworker0@xxxxxxxxx> 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@xxxxxx>
> > Signed-off-by: Lance Yang <ioworker0@xxxxxxxxx>
>
> Personally, I'm not convinced that using a temporary variable order
> makes the code
> more readable. Functions like folio_test_pmd_mappable() seem more readable to
> me. In any case, it's a minor issue.

Yes, I have the same opinion as Barry. With that:
Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>


> Acked-by: Barry Song <baohua@xxxxxxxxxx>
>
> > ---
> >   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
> > --
> > 2.45.2