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

[Lance Yang]

Hey Bang,

Thanks for taking time to review!

On Thu, Apr 25, 2024 at 1:59 AM Bang Li <libang.linux@xxxxxxxxx> wrote:
>
> Hey, sorry for making noise, there was something wrong with the format of
> the last email.
>
> On 2024/4/25 1:12, Bang Li wrote:
> > Hey Lance,
> >
> > On 2024/4/24 21:51, Lance Yang wrote:
> >
> >> At present, the split counters in THP statistics no longer include
> >> PTE-mapped mTHP. Therefore, this commit introduces per-order mTHP split
> >> counters to monitor the frequency of mTHP splits. This will assist
> >> developers in better analyzing and optimizing system performance.
> >>
> >> /sys/kernel/mm/transparent_hugepage/hugepages-<size>/stats
> >>          split_page
> >>          split_page_failed
> >>          deferred_split_page
> >>
> >> Signed-off-by: Lance Yang <ioworker0@xxxxxxxxx>
> >> ---
> >>   include/linux/huge_mm.h |  3 +++
> >>   mm/huge_memory.c        | 14 ++++++++++++--
> >>   2 files changed, 15 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> >> index 56c7ea73090b..7b9c6590e1f7 100644
> >> --- a/include/linux/huge_mm.h
> >> +++ b/include/linux/huge_mm.h
> >> @@ -272,6 +272,9 @@ enum mthp_stat_item {
> >>       MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE,
> >>       MTHP_STAT_ANON_SWPOUT,
> >>       MTHP_STAT_ANON_SWPOUT_FALLBACK,
> >> +    MTHP_STAT_SPLIT_PAGE,
> >> +    MTHP_STAT_SPLIT_PAGE_FAILED,
> >> +    MTHP_STAT_DEFERRED_SPLIT_PAGE,
> >>       __MTHP_STAT_COUNT
> >>   };
> >>   diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> >> index 055df5aac7c3..52db888e47a6 100644
> >> --- a/mm/huge_memory.c
> >> +++ b/mm/huge_memory.c
> >> @@ -557,6 +557,9 @@ 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(split_page, MTHP_STAT_SPLIT_PAGE);
> >> +DEFINE_MTHP_STAT_ATTR(split_page_failed, MTHP_STAT_SPLIT_PAGE_FAILED);
> >> +DEFINE_MTHP_STAT_ATTR(deferred_split_page,
> >> MTHP_STAT_DEFERRED_SPLIT_PAGE);
> >>     static struct attribute *stats_attrs[] = {
> >>       &anon_fault_alloc_attr.attr,
> >> @@ -564,6 +567,9 @@ static struct attribute *stats_attrs[] = {
> >>       &anon_fault_fallback_charge_attr.attr,
> >>       &anon_swpout_attr.attr,
> >>       &anon_swpout_fallback_attr.attr,
> >> +    &split_page_attr.attr,
> >> +    &split_page_failed_attr.attr,
> >> +    &deferred_split_page_attr.attr,
> >>       NULL,
> >>   };
> >>   @@ -3083,7 +3089,7 @@ 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;
> >> @@ -3262,8 +3268,10 @@ 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_PAGE :
> >> +                      MTHP_STAT_SPLIT_PAGE_FAILED);
> >>       return ret;
> >>   }
> >>   @@ -3327,6 +3335,8 @@ void deferred_split_folio(struct folio *folio)
> >>       if (list_empty(&folio->_deferred_list)) {
> >>           if (folio_test_pmd_mappable(folio))
> >>               count_vm_event(THP_DEFERRED_SPLIT_PAGE);
> >> +        count_mthp_stat(folio_order(folio),
> >> +                MTHP_STAT_DEFERRED_SPLIT_PAGE);
> >>           list_add_tail(&folio->_deferred_list, &ds_queue->split_queue);
> >>           ds_queue->split_queue_len++;
> >>   #ifdef CONFIG_MEMCG
> >
> > My opinion can be ignored :). Would it be better to modify the
> > deferred_split_folio
> > function as follows? I'm not sure.
> >
> > diff --git a/mm/huge_memory.c b/mm/huge_memory.c index
> > 055df5aac7c3..e8562e8630b1 100644 --- a/mm/huge_memory.c +++
> > b/mm/huge_memory.c @@ -3299,12 +3299,13 @@ void
> > deferred_split_folio(struct folio *folio) struct mem_cgroup *memcg =
> > folio_memcg(folio); #endif unsigned long flags; + int order =
> > folio_order(folio); /* * 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; /* @@ -3325,8 +3326,9 @@ 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_DEFERRED_SPLIT_PAGE); list_add_tail(&folio->_deferred_list,
> > &ds_queue->split_queue); ds_queue->split_queue_len++; #ifdef
> > CONFIG_MEMCG thanks,
> > bang
> >
>
> My opinion can be ignored :). Would it be better to modify the
> deferred_split_folio
> function as follows? I'm not sure.
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 055df5aac7c3..e8562e8630b1 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -3299,12 +3299,13 @@ void deferred_split_folio(struct folio *folio)
>          struct mem_cgroup *memcg = folio_memcg(folio);
>   #endif
>          unsigned long flags;
> +       int order = folio_order(folio);

I'll consider storing it in a variable earlier for later reuse.

Thanks,
Lance

>
>          /*
>           * 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;
>
>          /*
> @@ -3325,8 +3326,9 @@ 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_DEFERRED_SPLIT_PAGE);
>                  list_add_tail(&folio->_deferred_list,
> &ds_queue->split_queue);
>                  ds_queue->split_queue_len++;
>   #ifdef CONFIG_MEMCG
>
> thanks,
> bang