linux-kernel - Re: [PATCH] mm: memcg: provide accurate stats for userspace reads

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Message-ID: <ZNrLO5PAEZw4yjI9@slm.duckdns.org>
Date:   Mon, 14 Aug 2023 14:47:55 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Yosry Ahmed <yosryahmed@...gle.com>
Cc:     Michal Hocko <mhocko@...e.com>, Shakeel Butt <shakeelb@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Muchun Song <muchun.song@...ux.dev>, cgroups@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: memcg: provide accurate stats for userspace reads

Hello,

On Mon, Aug 14, 2023 at 05:39:15PM -0700, Yosry Ahmed wrote:
> I believe dropping unified flushing, if possible of course, may fix
> both problems.

Yeah, flushing the whole tree for every stat read will push up the big O
complexity of the operation. It shouldn't be too bad because only what's
updated since the last read will need flushing but if you have a really big
machine with a lot of constantly active cgroups, you're still gonna feel it.
So, yeah, drop that and switch the global lock to mutex and we should all be
good?

Thanks.

-- 
tejun