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

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Date:   Mon, 4 Sep 2017 10:35:00 +0900
From:   Kyeongdon Kim <kyeongdon.kim@....com>
To:     Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
        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: Re: [PATCH] mm/vmstats: add counters for the page frag cache

Thanks for your reply,
But I couldn't find "NR_FRAGMENT_PAGES" in linux-next.git .. is that 
vmstat counter? or others?

As you know, page_frag_alloc() directly calls __alloc_pages_nodemask() 
function,
so that makes too difficult to see memory usage in real time even though 
we have "/meminfo or /slabinfo.." information.
If there was a way already to figure out the memory leakage from 
page_frag_cache in mainline, I agree your opinion
but I think we don't have it now.

If those counters too much in my patch,
I can say two values (pgfrag_alloc and pgfrag_free) are enough to guess 
what will happen
and would remove pgfrag_alloc_calls and pgfrag_free_calls.

Thanks,
Kyeongdon Kim

On 2017-09-01 오후 6:12, Konstantin Khlebnikov wrote:
> 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>
> > ---