linux-kernel - Re: [PATCH] kvm, mm: account kvm related kmem slabs to kmemcg

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Date:   Fri, 6 Oct 2017 09:52:16 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Anshuman Khandual <khandual@...ux.vnet.ibm.com>
Cc:     Shakeel Butt <shakeelb@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Greg Thelen <gthelen@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kvm, mm: account kvm related kmem slabs to kmemcg

On Fri 06-10-17 09:58:30, Anshuman Khandual wrote:
> On 10/06/2017 06:37 AM, Shakeel Butt wrote:
> > The kvm slabs can consume a significant amount of system memory
> > and indeed in our production environment we have observed that
> > a lot of machines are spending significant amount of memory that
> > can not be left as system memory overhead. Also the allocations
> > from these slabs can be triggered directly by user space applications
> > which has access to kvm and thus a buggy application can leak
> > such memory. So, these caches should be accounted to kmemcg.
> 
> But there may be other situations like this where user space can
> trigger allocation from various SLAB objects inside the kernel
> which are accounted as system memory. So how we draw the line
> which ones should be accounted for memcg. Just being curious.

The thing is that we used to have an opt-out approach for kmem
accounting but we decided to go opt-in in a9bb7e620efd ("memcg: only
account kmem allocations marked as __GFP_ACCOUNT").

Since then we are adding the flag to caches/allocations which can go
wild and consume a lot of or even unbounded amount of memory.
-- 
Michal Hocko
SUSE Labs