linux-kernel - Re: [PATCH v3 2/2] mm: memcg: introduce new event to trace shrink

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Message-ID: <20231125174742.n3ybfum53yd27bo7@google.com>
Date:   Sat, 25 Nov 2023 17:47:42 +0000
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Dmitry Rokosov <ddrokosov@...utedevices.com>
Cc:     rostedt@...dmis.org, mhiramat@...nel.org, hannes@...xchg.org,
        mhocko@...nel.org, roman.gushchin@...ux.dev, muchun.song@...ux.dev,
        mhocko@...e.com, akpm@...ux-foundation.org, kernel@...rdevices.ru,
        rockosov@...il.com, cgroups@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH v3 2/2] mm: memcg: introduce new event to trace shrink_memcg

On Thu, Nov 23, 2023 at 10:39:37PM +0300, Dmitry Rokosov wrote:
> The shrink_memcg flow plays a crucial role in memcg reclamation.
> Currently, it is not possible to trace this point from non-direct
> reclaim paths. However, direct reclaim has its own tracepoint, so there
> is no issue there. In certain cases, when debugging memcg pressure,
> developers may need to identify all potential requests for memcg
> reclamation including kswapd(). The patchset introduces the tracepoints
> mm_vmscan_memcg_shrink_{begin|end}() to address this problem.
> 
> Example of output in the kswapd context (non-direct reclaim):
>     kswapd0-39      [001] .....   240.356378: mm_vmscan_memcg_shrink_begin: order=0 gfp_flags=GFP_KERNEL memcg=16
>     kswapd0-39      [001] .....   240.356396: mm_vmscan_memcg_shrink_end: nr_reclaimed=0 memcg=16
>     kswapd0-39      [001] .....   240.356420: mm_vmscan_memcg_shrink_begin: order=0 gfp_flags=GFP_KERNEL memcg=16
>     kswapd0-39      [001] .....   240.356454: mm_vmscan_memcg_shrink_end: nr_reclaimed=1 memcg=16
>     kswapd0-39      [001] .....   240.356479: mm_vmscan_memcg_shrink_begin: order=0 gfp_flags=GFP_KERNEL memcg=16
>     kswapd0-39      [001] .....   240.356506: mm_vmscan_memcg_shrink_end: nr_reclaimed=4 memcg=16
>     kswapd0-39      [001] .....   240.356525: mm_vmscan_memcg_shrink_begin: order=0 gfp_flags=GFP_KERNEL memcg=16
>     kswapd0-39      [001] .....   240.356593: mm_vmscan_memcg_shrink_end: nr_reclaimed=11 memcg=16
>     kswapd0-39      [001] .....   240.356614: mm_vmscan_memcg_shrink_begin: order=0 gfp_flags=GFP_KERNEL memcg=16
>     kswapd0-39      [001] .....   240.356738: mm_vmscan_memcg_shrink_end: nr_reclaimed=25 memcg=16
>     kswapd0-39      [001] .....   240.356790: mm_vmscan_memcg_shrink_begin: order=0 gfp_flags=GFP_KERNEL memcg=16
>     kswapd0-39      [001] .....   240.357125: mm_vmscan_memcg_shrink_end: nr_reclaimed=53 memcg=16
> 
> Signed-off-by: Dmitry Rokosov <ddrokosov@...utedevices.com>

Acked-by: Shakeel Butt <shakeelb@...gle.com>