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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Fri, 11 Aug 2023 19:35:49 -0700
From:   Yosry Ahmed <yosryahmed@...gle.com>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     Michal Hocko <mhocko@...e.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

On Fri, Aug 11, 2023 at 7:29 PM Shakeel Butt <shakeelb@...gle.com> wrote:
>
> On Fri, Aug 11, 2023 at 7:12 PM Yosry Ahmed <yosryahmed@...gle.com> wrote:
> >
> [...]
> >
> > I am worried that writing to a stat for flushing then reading will
> > increase the staleness window which we are trying to reduce here.
> > Would it be acceptable to add a separate interface to explicitly read
> > flushed stats without having to write first? If the distinction
> > disappears in the future we can just short-circuit both interfaces.
>
> What is the acceptable staleness time window for your case? It is hard
> to imagine that a write+read will always be worse than just a read.
> Even the proposed patch can have an unintended and larger than
> expected staleness window due to some processing on
> return-to-userspace or some scheduling delay.

Maybe I am worrying too much, we can just go for writing to
memory.stat for explicit stats refresh.

Do we still want to go with the mutex approach Michal suggested for
do_flush_stats() to support either waiting for ongoing flushes
(mutex_lock) or skipping (mutex_trylock)?