linux-kernel - Re: [PATCH v2] mm: implement write-behind policy for sequential file writes

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Message-ID: <CAHk-=wi+G1MfSu79Ayi-yxbmhdyuLnZ5e1tmBTc69v9Zvd-NKg@mail.gmail.com>
Date:   Fri, 20 Sep 2019 16:10:01 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Cc:     linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jens Axboe <axboe@...nel.dk>, Michal Hocko <mhocko@...e.com>,
        Dave Chinner <david@...morbit.com>,
        Mel Gorman <mgorman@...e.de>,
        Johannes Weiner <hannes@...xchg.org>, Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH v2] mm: implement write-behind policy for sequential file writes

On Fri, Sep 20, 2019 at 4:05 PM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
>
> Now, I hear you say "those are so small these days that it doesn't
> matter". And maybe you're right. But particularly for slow media,
> triggering good streaming write behavior has been a problem in the
> past.

Which reminds me: the writebehind trigger should likely be tied to the
estimate of the bdi write speed.

We _do_ have that avg_write_bandwidth thing in the bdi_writeback
structure, it sounds like a potentially good idea to try to use that
to estimate when to do writebehind.

No?

            Linus