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

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Message-ID: <4F0B7D1F.7040802@gmail.com>
Date:	Mon, 09 Jan 2012 18:49:51 -0500
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	Rik van Riel <riel@...hat.com>
CC:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, Mel Gorman <mel@....ul.ie>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH -mm] make swapin readahead skip over holes

(1/9/12 6:10 PM), 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.

If I understand correctly, this patch have

Pros
  - increase IO throughput
Cons
  - increase a risk to pick up unrelated swap entries by swap readahead


The changelog explained former but doesn't explained latter. I'm a bit
hesitate now.
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