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

From: Michal Hocko
Date: Fri Oct 06 2017 - 03:52:22 EST

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