linux-kernel - Re: [PATCH v4 -mm] make swapin readahead skip over holes

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Message-ID: <20120125105138.GA3901@csn.ul.ie>
Date:	Wed, 25 Jan 2012 10:51:38 +0000
From:	Mel Gorman <mel@....ul.ie>
To:	Rik van Riel <riel@...hat.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Minchan Kim <minchan.kim@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Adrian Drzewieki <z@...e.net>
Subject: Re: [PATCH v4 -mm] make swapin readahead skip over holes

On Tue, Jan 24, 2012 at 02:14:00PM -0500, Rik van Riel wrote:
> Ever since abandoning the virtual scan of processes, for scalability
> reasons, swap space has been a little more fragmented than before.
> This can lead to the situation where a large memory user is killed,
> swap space ends up full of "holes" and swapin readahead is totally
> ineffective.
> 
> On my home system, after killing a leaky firefox it took over an
> hour to page just under 2GB of memory back in, slowing the virtual
> machines down to a crawl.
> 
> This patch makes swapin readahead simply skip over holes, instead
> of stopping at them.  This allows the system to swap things back in
> at rates of several MB/second, instead of a few hundred kB/second.
> 
> The checks done in valid_swaphandles are already done in 
> read_swap_cache_async as well, allowing us to remove a fair amount
> of code.
> 
> Signed-off-by: Rik van Riel <riel@...hat.com>

Acked-by: Mel Gorman <mgorman@...e.de>

-- 
Mel Gorman
SUSE Labs
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