linux-kernel - Re: [PATCH 1/4] memcg: simplify consume

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Message-ID: <a2925f3d-9af0-4299-aafa-70dfaf0f3230@suse.cz>
Date: Wed, 7 May 2025 13:43:06 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Shakeel Butt <shakeel.butt@...ux.dev>,
 Andrew Morton <akpm@...ux-foundation.org>
Cc: Johannes Weiner <hannes@...xchg.org>, Michal Hocko <mhocko@...nel.org>,
 Roman Gushchin <roman.gushchin@...ux.dev>,
 Muchun Song <muchun.song@...ux.dev>, Alexei Starovoitov <ast@...nel.org>,
 Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
 Jakub Kicinski <kuba@...nel.org>, Eric Dumazet <edumazet@...gle.com>,
 linux-mm@...ck.org, cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
 bpf@...r.kernel.org, netdev@...r.kernel.org,
 Meta kernel team <kernel-team@...a.com>
Subject: Re: [PATCH 1/4] memcg: simplify consume_stock

On 5/7/25 12:55 AM, Shakeel Butt wrote:
> The consume_stock() does not need to check gfp_mask for spinning and can
> simply trylock the local lock to decide to proceed or fail. No need to
> spin at all for local lock.
> 
> One of the concern raised was that on PREEMPT_RT kernels, this trylock
> can fail more often due to tasks having lock_lock can be preempted. This
> can potentially cause the task which have preempted the task having the
> local_lock to take the slow path of memcg charging.
> 
> However this behavior will only impact the performance if memcg charging
> slowpath is worse than two context switches and possibly scheduling
> delay behavior of current code. From the network intensive workload
> experiment it does not seem like the case.
> 
> We ran varying number of netperf clients in different cgroups on a 72 CPU
> machine for PREEMPT_RT config.
> 
>  $ netserver -6
>  $ netperf -6 -H ::1 -l 60 -t TCP_SENDFILE -- -m 10K
> 
> number of clients | Without series | With series
>   6               | 38559.1 Mbps   | 38652.6 Mbps
>   12              | 37388.8 Mbps   | 37560.1 Mbps
>   18              | 30707.5 Mbps   | 31378.3 Mbps
>   24              | 25908.4 Mbps   | 26423.9 Mbps
>   30              | 22347.7 Mbps   | 22326.5 Mbps
>   36              | 20235.1 Mbps   | 20165.0 Mbps
> 
> We don't see any significant performance difference for the network
> intensive workload with this series.
> 
> Signed-off-by: Shakeel Butt <shakeel.butt@...ux.dev>

Reviewed-by: Vlastimil Babka <vbabka@...e.cz>