linux-kernel - Re: [PATCH] memcg: sync flush only if periodic flush is delayed

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:   Mon, 14 Mar 2022 13:57:09 +0100
From:   Michal Koutný <mkoutny@...e.com>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Ivan Babrou <ivan@...udflare.com>,
        Frank Hofmann <fhofmann@...udflare.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        cgroups@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Daniel Dao <dqminh@...udflare.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH] memcg: sync flush only if periodic flush is delayed

Hi 2.

On Sat, Mar 12, 2022 at 07:07:15PM +0000, Shakeel Butt <shakeelb@...gle.com> wrote:
> It is (b) that I am aiming for in this patch. At least (a) was not
> happening in the cloudflare experiments. Are you suggesting having a
> dedicated high priority wq would solve both (a) and (b)?
> [...]
> > We can't argue what's the effect of periodic only flushing so this
> > newly introduced factor would inherit that too. I find it superfluous.
> 
> 
> Sorry I didn't get your point. What is superfluous?

Let me retell my understanding.
The current implementation flushes based on cumulated error and time.
Your patch proposes conditioning the former with another time-based
flushing, whose duration can be up to 2 times longer than the existing
periodic flush.

Assuming the periodic flush is working, the reader won't see data older
than 2 seconds, so the additional sync-flush after (possible) 4 seconds
seems superfluous.

(In the case of periodic flush being stuck, I thought the factor 2=4s/2s
was superfluous, another magic parameter.)

I'm comparing here your proposal vs no synchronous flushing in
workingset_refault().

> Do you have any strong concerns with the currect patch?

Does that clarify?

(I agree with your initial thesis this can be iterated before it evolves
to everyone's satisfaction.)


Michal