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

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Message-ID: <CAM43=SOAU2-qTB2cHeZs5xGzPFKwoqtTafqtw+BqCP9cbQDUOQ@mail.gmail.com>
Date:   Mon, 27 Nov 2017 20:28:27 +0100
From:   Mikael Pettersson <mikpelinux@...il.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Michal Hocko <mhocko@...nel.org>, linux-mm@...ck.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-fsdevel@...r.kernel.org,
        Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH] mm: disable `vm.max_map_count' sysctl limit

On Mon, Nov 27, 2017 at 5:22 PM, Matthew Wilcox <willy@...radead.org> wrote:
>> 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.

Exactly, except the origin (mmap() failing) was hidden behind layers upon layers
of user-space memory management code (not ours), which just said "failed to
allocate N bytes" (with N about 0.001% of the free RAM).  And it
wasn't reproducible.