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

From: Vladimir Davydov
Date: Mon Aug 31 2015 - 11:24:56 EST

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.

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