linux-kernel - Re: [RFC][PATCH 0/6] more detailed per-process transparent hugepage statistics

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Message-ID: <1297187674.6737.12145.camel@nimitz>
Date:	Tue, 08 Feb 2011 09:54:34 -0800
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	Andrea Arcangeli <aarcange@...hat.com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Michael J Wolf <mjwolf@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC][PATCH 0/6] more detailed per-process transparent
 hugepage statistics

On Wed, 2011-02-02 at 01:07 +0100, Andrea Arcangeli wrote:
> > I guess we could also try and figure out whether the khugepaged CPU
> > overhead really comes from the scanning or the collapsing operations
> > themselves.  Should be as easy as some oprofiling.
> 
> Actually I already know, the scanning is super fast. So it's no real
> big deal to increase the scanning. It's big deal only if there are
> plenty more of collapse/split. Compared to the KSM scan, the
> khugepaged scan costs nothing.

Just FYI, I did some profiling on a workload that constantly split and
joined pages.  Very little of the overhead was in the scanning itself,
so I think you're dead-on here.

-- Dave

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