linux-kernel - Re: [PATCH v2] Make transparent hugepages cpuset aware

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Message-ID: <alpine.DEB.2.02.1306191939250.24151@chino.kir.corp.google.com>
Date:	Wed, 19 Jun 2013 19:43:23 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Robin Holt <holt@....com>
cc:	Alex Thorlton <athorlton@....com>, linux-kernel@...r.kernel.org,
	Li Zefan <lizefan@...wei.com>, Rob Landley <rob@...dley.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>,
	linux-doc@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v2] Make transparent hugepages cpuset aware

On Wed, 19 Jun 2013, Robin Holt wrote:

> cpusets was not for NUMA.  It has no preference for "nodes" or anything like
> that.  It was for splitting a machine into layered smaller groups.  Usually,
> we see one cpuset with contains the batch scheduler.  The batch scheduler then
> creates cpusets for jobs it starts.  Has nothing to do with nodes.  That is
> more an administrator issue.  They set the minimum grouping of resources
> for scheduled jobs.
> 

I disagree with all of the above, it's not what Paul Jackson developed 
cpusets for, it's not what he wrote in Documentation/cgroups/cpusets.txt, 
and it's not why libnuma immediately supported it.  Cpusets is for NUMA, 
like it or not.

> > I'm saying there's absolutely no reason to have thp controlled by a 
> > cpuset, or ANY cgroup for that matter, since you chose not to respond to 
> > the question I asked: why do you want to control thp behavior for certain 
> > static binaries and not others?  Where is the performance regression or 
> > the downside?  Is it because of max_ptes_none for certain jobs blowing up 
> > the rss?  We need information, and even if were justifiable then it 
> > wouldn't have anything to do with ANY cgroup but rather a per-process 
> > control.  It has nothing to do with cpusets whatsoever.
> 
> It was a request from our benchmarking group that has found some jobs
> benefit from thp, while other are harmed.  Let me ask them for more
> details.
> 

Yes, please, because if some jobs are harmed by thp then we need to fix 
that regression and not paper around with it with some cpuset-based 
solution.  People should be able to run with CONFIG_TRANSPARENT_HUGEPAGE 
enabled and not be required to enable CONFIG_CPUSETS for optimal behavior.  
I'm suspecting that you're referring to enlarged rss because of 
khugepaged's max_ptes_none and because you're abusing the purpose of 
cpusets for containerization.
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