linux-kernel - Re: [rfc][patch] swap: virtual swap readahead

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Message-ID: <4A1D7935.10000@redhat.com>
Date:	Wed, 27 May 2009 13:32:37 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Johannes Weiner <hannes@...xchg.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Hugh Dickins <hugh.dickins@...cali.co.uk>
Subject: Re: [rfc][patch] swap: virtual swap readahead

Johannes Weiner wrote:

> This patch makes swap-in base its readaround window on the virtual
> proximity of pages in the faulting VMA, as an indicator for pages
> needed in the near future, while still taking physical locality of
> swap slots into account.
> 
> This has the advantage of reading in big batches when the LRU order
> matches the swap slot order while automatically throttling readahead
> when the system is thrashing and swap slots are no longer nicely
> grouped by LRU order.

This is a nice simple implementation of proper
swapin readahead.  The performance results are
surprisingly good.

I suspect the performance oddity you see with
single-process qsbench might be due to qsbench
having a weird access pattern that just happens
to benefit from getting pages back into memory
in LRU order - not something that I expect to
be common, so not a concern.

> Signed-off-by: Johannes Weiner <hannes@...xchg.org>
> Cc: Hugh Dickins <hugh.dickins@...cali.co.uk>
> Cc: Rik van Riel <riel@...hat.com>

Reviewed-by: Rik van Riel <riel@...hat.com>
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