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

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Date:   Mon, 27 Nov 2017 19:32:18 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Andi Kleen <ak@...ux.intel.com>
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 27-11-17 09:25:16, Andi Kleen wrote:
> Michal Hocko <mhocko@...nel.org> writes:
> >
> > 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.
> 
> It's an arbitrary scaling limit on the how many mappings the process
> has. The more memory you have the bigger a problem it is. We've
> ran into this problem too on larger systems.

Why cannot you increase the limit?

> The reason the limit was there originally because it allows a DoS
> attack against the kernel by filling all unswappable memory up with VMAs.

We can reduce the effect by accounting vmas to memory cgroups.
-- 
Michal Hocko
SUSE Labs