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

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Date: Thu, 25 Apr 2024 01:12:49 +0800
From: Bang Li <libang.linux@...il.com>
To: Lance Yang <ioworker0@...il.com>
Cc: akpm@...ux-foundation.org, 21cnbao@...il.com, ryan.roberts@....com,
 david@...hat.com, baolin.wang@...ux.alibaba.com,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 1/2] mm: add per-order mTHP split counters

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@...il.com>
> ---
>   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