linux-kernel - Re: [PATCH 0/2] Fix memcg/memory.high in case kmem accounting is enabled

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Date:	Mon, 31 Aug 2015 18:24:36 +0300
From:	Vladimir Davydov <vdavydov@...allels.com>
To:	Tejun Heo <tj@...nel.org>
CC:	Michal Hocko <mhocko@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/2] Fix memcg/memory.high in case kmem accounting is
 enabled

On Mon, Aug 31, 2015 at 10:46:04AM -0400, Tejun Heo wrote:
> Hello, Vladimir.
> 
> On Mon, Aug 31, 2015 at 05:20:49PM +0300, Vladimir Davydov wrote:
> ...
> > That being said, this is the fix at the right layer.
> 
> While this *might* be a necessary workaround for the hard limit case
> right now, this is by no means the fix at the right layer.  The
> expectation is that mm keeps a reasonable amount of memory available
> for allocations which can't block.  These allocations may fail from
> time to time depending on luck and under extreme memory pressure but
> the caller should be able to depend on it as a speculative allocation
> mechanism which doesn't fail willy-nilly.
> 
> Hardlimit breaking GFP_NOWAIT behavior is a bug on memcg side, not
> slab or slub.

I never denied that there is GFP_NOWAIT/GFP_NOFS problem in memcg. I
even proposed ways to cope with it in one of the previous e-mails.

Nevertheless, we just can't allow slab/slub internals call memcg_charge
whenever they want as I pointed out in a parallel thread.

Thanks,
Vladimir
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