linux-kernel - Re: [PATCH] Increase default MLOCK

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Date:   Thu, 18 Nov 2021 13:58:46 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Ammar Faizi <ammarfaizi2@...weeb.org>,
        Drew DeVault <sir@...wn.com>, linux-kernel@...r.kernel.org,
        linux-api@...r.kernel.org,
        io_uring Mailing List <io-uring@...r.kernel.org>,
        Pavel Begunkov <asml.silence@...il.com>, linux-mm@...ck.org
Subject: Re: [PATCH] Increase default MLOCK_LIMIT to 8 MiB

On Wed, 17 Nov 2021 16:17:26 -0700 Jens Axboe <axboe@...nel.dk> wrote:

> On 11/17/21 3:26 PM, Johannes Weiner wrote:
> >> Link: https://lkml.kernel.org/r/20211028080813.15966-1-sir@cmpwn.com
> >> Signed-off-by: Drew DeVault <sir@...wn.com>
> >> Acked-by: Jens Axboe <axboe@...nel.dk>
> >> Acked-by: Cyril Hrubis <chrubis@...e.cz>
> >> Cc: Pavel Begunkov <asml.silence@...il.com>
> >> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> > 
> > Acked-by: Johannes Weiner <hannes@...xchg.org>
> > 
> > As per above, I think basing it off of RAM size would be better, but
> > this increase is overdue given all the new users beyond mlock(), and
> > 8M is much better than the current value.
> 
> That's basically my reasoning too. Let's just get something going that
> will at least unblock some valid use cases, and not get bogged down with
> aiming for perfection. The latter can happen in parallel, but it should
> not hold it up imho.

Nobody's aiming for perfection.  We're discussing aiming for "better".

What we should have done on day one was to set the default MLOCK_LIMIT
to zero bytes.  Then everyone would have infrastructure to tune it from
userspace and we wouldn't ever have this discussion.