Re: [patch] mm: memcontrol: support transparent huge pages under pressure

[Vladimir Davydov]

On Tue, Sep 23, 2014 at 12:29:27PM +0400, Vladimir Davydov wrote:
> On Mon, Sep 22, 2014 at 10:52:50PM -0700, Greg Thelen wrote:
> > In this condition, if res usage is at limit then there's no point in
> > swapping because memsw.usage is already maximal.  Prior to this patch
> > I think the kernel did the right thing, but not afterwards.
> > 
> > Before this patch:
> >   if res.usage == res.limit, try_charge() indirectly calls
> >   try_to_free_mem_cgroup_pages(noswap=true)
> 
> But this is wrong. If we fail to charge res, we should try to do swap
> out along with page cache reclaim. Swap out won't affect memsw.usage,
> but will diminish res.usage so that the allocation may succeed.

Oops, I missed your point, sorry. If we hit the res.limit and
memsw.limit=res.limit, we automatically hit memsw.limit too, so there's
no point swapping out.

Thanks,
Vladimir
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