linux-kernel - Re: [mm-unstable v4 5/5] mm: memcg: restore subtree stats flushing

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Message-ID: <20231204235856.k4izppfsrpg2rng7@google.com>
Date:   Mon, 4 Dec 2023 23:58:56 +0000
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Yosry Ahmed <yosryahmed@...gle.com>
Cc:     Wei Xu <weixugc@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Muchun Song <muchun.song@...ux.dev>,
        Ivan Babrou <ivan@...udflare.com>, Tejun Heo <tj@...nel.org>,
        "Michal Koutný" <mkoutny@...e.com>,
        Waiman Long <longman@...hat.com>, kernel-team@...udflare.com,
        Greg Thelen <gthelen@...gle.com>,
        Domenico Cerasuolo <cerasuolodomenico@...il.com>,
        linux-mm@...ck.org, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [mm-unstable v4 5/5] mm: memcg: restore subtree stats flushing

On Mon, Dec 04, 2023 at 03:49:01PM -0800, Yosry Ahmed wrote:
[...]
> 
> From 19af26e01f93cbf0806d75a234b78e48c1ce9d80 Mon Sep 17 00:00:00 2001
> From: Yosry Ahmed <yosryahmed@...gle.com>
> Date: Mon, 4 Dec 2023 23:43:29 +0000
> Subject: [PATCH] mm: memcg: remove stats flushing mutex
> 
> The mutex was intended to make the waiters sleep instead of spin, and
> such that we can check the update thresholds again after acquiring the
> mutex. However, the mutex has a risk of priority inversion, especially
> since the underlying rstat lock can de dropped while the mutex is held.
> 
> Synthetic testing with high concurrency of flushers shows no
> regressions without the mutex, so remove it.
> 
> Suggested-by: Shakeel Butt <shakeelb@...gle.com>
> Signed-off-by: Yosry Ahmed <yosryahmed@...gle.com>

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