linux-kernel - Re: [PATCH -mm 2/2] mm: kswapd carefully invoke compaction

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Date:	Wed, 11 Jan 2012 02:25:26 -0500
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	linux-mm@...ck.org, aarcange@...hat.com,
	linux-kernel@...r.kernel.org, Mel Gorman <mel@....ul.ie>,
	akpm@...ux-foundation.org, Johannes Weiner <hannes@...xchg.org>,
	hughd@...gle.com
Subject: Re: [PATCH -mm 2/2] mm: kswapd carefully invoke compaction

> With CONFIG_COMPACTION enabled, kswapd does not try to free
> contiguous free pages, even when it is woken for a higher order
> request.
>
> This could be bad for eg. jumbo frame network allocations, which
> are done from interrupt context and cannot compact memory themselves.
> Higher than before allocation failure rates in the network receive
> path have been observed in kernels with compaction enabled.
>
> Teach kswapd to defragment the memory zones in a node, but only
> if required and compaction is not deferred in a zone.
>
> Signed-off-by: Rik van Riel <riel@...hat.com>

I agree with we need asynchronous defragmentations feature. But, do we
really need to use kswapd for compaction? While kswapd take a
compaction work, it can't work to make
free memory.
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