linux-kernel - Re: [PATCH 15/15] readahead: pagecache context based mmap read-around

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Message-ID: <4B8724EC.1090904@redhat.com>
Date:	Thu, 25 Feb 2010 20:33:32 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Wu Fengguang <fengguang.wu@...el.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Jens Axboe <jens.axboe@...cle.com>,
	Nick Piggin <npiggin@...e.de>,
	Chris Mason <chris.mason@...cle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Clemens Ladisch <clemens@...isch.de>,
	Olivier Galibert <galibert@...ox.com>,
	Vivek Goyal <vgoyal@...hat.com>,
	Christian Ehrhardt <ehrhardt@...ux.vnet.ibm.com>,
	Matt Mackall <mpm@...enic.com>,
	Linux Memory Management List <linux-mm@...ck.org>,
	linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 15/15] readahead: pagecache context based mmap read-around

On 02/23/2010 10:10 PM, Wu Fengguang wrote:
> Do mmap read-around when there are cached pages in the nearby 256KB
> (covered by one radix tree node).
>
> There is a failure case though: for a sequence of page faults at page
> index 64*i+1, i=1,2,3,..., this heuristic will keep doing pointless
> read-arounds.  Hopefully the pattern won't appear in real workloads.
> Note that the readahead heuristic has similiar failure case.
>
> CC: Nick Piggin<npiggin@...e.de>
> Signed-off-by: Wu Fengguang<fengguang.wu@...el.com>

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

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