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

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Date: Mon, 1 Jul 2024 12:02:14 +1200
From: Barry Song <21cnbao@...il.com>
To: Lance Yang <ioworker0@...il.com>
Cc: akpm@...ux-foundation.org, dj456119@...il.com, ryan.roberts@....com, 
	david@...hat.com, shy828301@...il.com, ziy@...dia.com, libang.li@...group.com, 
	baolin.wang@...ux.alibaba.com, linux-kernel@...r.kernel.org, 
	linux-mm@...ck.org, Mingzhe Yang <mingzhe.yang@...com>
Subject: Re: [PATCH v2 1/2] mm: add per-order mTHP split counters

On Sat, Jun 29, 2024 at 1:09 AM Lance Yang <ioworker0@...il.com> 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@...com>
> Signed-off-by: Lance Yang <ioworker0@...il.com>

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.

Acked-by: Barry Song <baohua@...nel.org>

> ---
>  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
>