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

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Date:   Mon, 27 Nov 2017 21:52:10 +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 12:21:21, Andi Kleen wrote:
> On Mon, Nov 27, 2017 at 08:57:32PM +0100, Michal Hocko wrote:
> > On Mon 27-11-17 19:32:18, Michal Hocko wrote:
> > > On Mon 27-11-17 09:25:16, Andi Kleen wrote:
> > [...]
> > > > 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.
> > 
> > As it turned out we already do.
> > 	vm_area_cachep = KMEM_CACHE(vm_area_struct, SLAB_PANIC|SLAB_ACCOUNT);
> 
> That only helps if you have memory cgroups enabled. It would be a regression
> to break the accounting on all the systems that don't.

I agree. And I didn't say we should remove the existing limit. I am just
saying that we can reduce existing problems by increasing the limit and
relying on memcg accounting where possible.
-- 
Michal Hocko
SUSE Labs