linux-kernel - Re: [BUG] mm, thp: khugepaged can't allocate on requested node when confined to a cpuset

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Message-ID: <20141014145435.GA7369@worktop.fdxtended.com>
Date:	Tue, 14 Oct 2014 16:54:35 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
Cc:	Alex Thorlton <athorlton@....com>, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Ingo Molnar <mingo@...nel.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Hugh Dickins <hughd@...gle.com>, Bob Liu <lliubbo@...il.com>,
	Johannes Weiner <hannes@...xchg.org>, linux-mm@...ck.org
Subject: Re: [BUG] mm, thp: khugepaged can't allocate on requested node when
 confined to a cpuset

On Tue, Oct 14, 2014 at 02:48:28PM +0300, Kirill A. Shutemov wrote:

> Why whould you want to pin khugpeaged? Is there a valid use-case?
> Looks like userspace shoots to its leg.

Its just bad design to put so much work in another context. But the
use-case is isolating other cpus.

> Is there a reason why we should respect cpuset limitation for kernel
> threads?

Yes, because we want to allow isolating CPUs from 'random' activity.

> Should we bypass cpuset for PF_KTHREAD completely?

No. That'll break stuff.
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