linux-kernel - Re: [PATCH 0/4] Convert khugepaged to a task

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Message-ID: <87lho0pf4l.fsf@tassilo.jf.intel.com>
Date:	Tue, 28 Oct 2014 05:12:26 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	Alex Thorlton <athorlton@....com>
Cc:	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	Bob Liu <lliubbo@...il.com>,
	David Rientjes <rientjes@...gle.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Hugh Dickins <hughd@...gle.com>,
	Ingo Molnar <mingo@...hat.com>,
	Kees Cook <keescook@...omium.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Mel Gorman <mgorman@...e.de>, Oleg Nesterov <oleg@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Rik van Riel <riel@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Vladimir Davydov <vdavydov@...allels.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/4] Convert khugepaged to a task_work function

Alex Thorlton <athorlton@....com> writes:

> Last week, while discussing possible fixes for some unexpected/unwanted behavior
> from khugepaged (see: https://lkml.org/lkml/2014/10/8/515) several people
> mentioned possibly changing changing khugepaged to work as a task_work function
> instead of a kernel thread.  This will give us finer grained control over the
> page collapse scans, eliminate some unnecessary scans since tasks that are
> relatively inactive will not be scanned often, and eliminate the unwanted
> behavior described in the email thread I mentioned.

With your change, what would happen in a single threaded case?

Previously one core would scan and another would run the workload.
With your change both scanning and running would be on the same
core.

Would seem like a step backwards to me.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only
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