linux-kernel - Re: [PATCH] mm: disable `vm.max_map

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Date:   Mon, 27 Nov 2017 08:22:07 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Mikael Pettersson <mikpelinux@...il.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-api@...r.kernel.org
Subject: Re: [PATCH] mm: disable `vm.max_map_count' sysctl limit

On Mon, Nov 27, 2017 at 11:12:32AM +0100, Michal Hocko wrote:
> On Sun 26-11-17 17:09:32, Mikael Pettersson wrote:
> > - Reaching the limit causes various memory management system calls to
> >   fail with ENOMEM, which is a lie.  Combined with the unpredictability
> >   of the number of mappings in a process, especially when non-trivial
> >   memory management or heavy file mapping is used, it can be difficult
> >   to reproduce these events and debug them.  It's also confusing to get
> >   ENOMEM when you know you have lots of free RAM.

[snip]

> Could you be more explicit about _why_ we need to remove this tunable?
> I am not saying I disagree, the removal simplifies the code but I do not
> really see any justification here.

I imagine he started seeing random syscalls failing with ENOMEM and
eventually tracked it down to this stupid limit we used to need.