linux-kernel - Re: [PATCH] mm/vmstats: add counters for the page frag cache

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Message-ID: <50592560-af4d-302c-c0bc-1e854e35139d@yandex-team.ru>
Date:   Fri, 1 Sep 2017 12:12:36 +0300
From:   Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
To:     Kyeongdon Kim <kyeongdon.kim@....com>, akpm@...ux-foundation.org,
        sfr@...b.auug.org.au
Cc:     ying.huang@...el.com, vbabka@...e.cz, hannes@...xchg.org,
        xieyisheng1@...wei.com, luto@...nel.org, shli@...com,
        mhocko@...e.com, mgorman@...hsingularity.net,
        hillf.zj@...baba-inc.com, kemi.wang@...el.com, rientjes@...gle.com,
        bigeasy@...utronix.de, iamjoonsoo.kim@....com, bongkyu.kim@....com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm/vmstats: add counters for the page frag cache

IMHO that's too much counters.
Per-node NR_FRAGMENT_PAGES should be enough for guessing what's going on.
Perf probes provides enough features for furhter debugging.

On 01.09.2017 02:37, Kyeongdon Kim wrote:
> There was a memory leak problem when we did stressful test
> on Android device.
> The root cause of this was from page_frag_cache alloc
> and it was very hard to find out.
> 
> We add to count the page frag allocation and free with function call.
> The gap between pgfrag_alloc and pgfrag_free is good to to calculate
> for the amount of page.
> The gap between pgfrag_alloc_calls and pgfrag_free_calls is for
> sub-indicator.
> They can see trends of memory usage during the test.
> Without it, it's difficult to check page frag usage so I believe we
> should add it.
> 
> Signed-off-by: Kyeongdon Kim <kyeongdon.kim@....com>
> ---
>   include/linux/vm_event_item.h | 4 ++++
>   mm/page_alloc.c               | 9 +++++++--
>   mm/vmstat.c                   | 4 ++++
>   3 files changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
> index d77bc35..75425d4 100644
> --- a/include/linux/vm_event_item.h
> +++ b/include/linux/vm_event_item.h
> @@ -110,6 +110,10 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
>   		SWAP_RA,
>   		SWAP_RA_HIT,
>   #endif
> +		PGFRAG_ALLOC,
> +		PGFRAG_FREE,
> +		PGFRAG_ALLOC_CALLS,
> +		PGFRAG_FREE_CALLS,
>   		NR_VM_EVENT_ITEMS
>   };
>   
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index db2d25f..b3ddd76 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -4322,6 +4322,7 @@ void __page_frag_cache_drain(struct page *page, unsigned int count)
>   			free_hot_cold_page(page, false);
>   		else
>   			__free_pages_ok(page, order);
> +		__count_vm_events(PGFRAG_FREE, 1 << order);
>   	}
>   }
>   EXPORT_SYMBOL(__page_frag_cache_drain);
> @@ -4338,7 +4339,7 @@ void *page_frag_alloc(struct page_frag_cache *nc,
>   		page = __page_frag_cache_refill(nc, gfp_mask);
>   		if (!page)
>   			return NULL;
> -
> +		__count_vm_events(PGFRAG_ALLOC, 1 << compound_order(page));
>   #if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE)
>   		/* if size can vary use size else just use PAGE_SIZE */
>   		size = nc->size;
> @@ -4375,6 +4376,7 @@ void *page_frag_alloc(struct page_frag_cache *nc,
>   
>   	nc->pagecnt_bias--;
>   	nc->offset = offset;
> +	__count_vm_event(PGFRAG_ALLOC_CALLS);
>   
>   	return nc->va + offset;
>   }
> @@ -4387,8 +4389,11 @@ void page_frag_free(void *addr)
>   {
>   	struct page *page = virt_to_head_page(addr);
>   
> -	if (unlikely(put_page_testzero(page)))
> +	if (unlikely(put_page_testzero(page))) {
> +		__count_vm_events(PGFRAG_FREE, 1 << compound_order(page));
>   		__free_pages_ok(page, compound_order(page));
> +	}
> +	__count_vm_event(PGFRAG_FREE_CALLS);
>   }
>   EXPORT_SYMBOL(page_frag_free);
>   
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index 4bb13e7..c00fe05 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -1217,6 +1217,10 @@ const char * const vmstat_text[] = {
>   	"swap_ra",
>   	"swap_ra_hit",
>   #endif
> +	"pgfrag_alloc",
> +	"pgfrag_free",
> +	"pgfrag_alloc_calls",
> +	"pgfrag_free_calls",
>   #endif /* CONFIG_VM_EVENTS_COUNTERS */
>   };
>   #endif /* CONFIG_PROC_FS || CONFIG_SYSFS || CONFIG_NUMA */
>