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

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Message-ID: <alpine.DEB.2.02.1306111517200.6141@chino.kir.corp.google.com>
Date:	Tue, 11 Jun 2013 15:20:09 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Alex Thorlton <athorlton@....com>
cc:	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 Tue, 11 Jun 2013, Alex Thorlton wrote:

> This patch adds the ability to control THPs on a per cpuset basis.  Please see
> the additions to Documentation/cgroups/cpusets.txt for more information.
> 

What's missing from both this changelog and the documentation you point to 
is why this change is needed.

I can understand how you would want a subset of processes to not use thp 
when it is enabled.  This is typically where MADV_NOHUGEPAGE is used with 
some type of malloc hook.

I don't think we need to do this on a cpuset level, so unfortunately I 
think this needs to be reworked.  Would it make sense to add a per-process 
tunable to always get MADV_NOHUGEPAGE behavior for all of its sbrk() and 
mmap() calls?  Perhaps, but then you would need to justify why it can't be 
done with a malloc hook in userspace.

This seems to just be working around a userspace issue or for a matter of 
convenience, right?
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