linux-kernel - Re: [PATCH 5/9] readahead: on-demand readahead logic

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Message-Id: <20070518232335.8a4c8247.akpm@linux-foundation.org>
Date:	Fri, 18 May 2007 23:23:35 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Fengguang Wu <wfg@...l.ustc.edu.cn>
Cc:	linux-kernel@...r.kernel.org, Andi Kleen <andi@...stfloor.org>,
	Jens Axboe <jens.axboe@...cle.com>,
	Oleg Nesterov <oleg@...sign.ru>,
	Steven Pratt <slpratt@...tin.ibm.com>,
	Ram Pai <linuxram@...ibm.com>
Subject: Re: [PATCH 5/9] readahead: on-demand readahead logic

On Thu, 17 May 2007 06:47:57 +0800 Fengguang Wu <wfg@...l.ustc.edu.cn> wrote:

> This is a minimal readahead algorithm that aims to replace the current one.
> It is more flexible and reliable, while maintaining almost the same behavior
> and performance. Also it is full integrated with adaptive readahead.
> 
> It is designed to be called on demand:
> 	- on a missing page, to do synchronous readahead
> 	- on a lookahead page, to do asynchronous readahead
> 
> In this way it eliminated the awkward workarounds for cache hit/miss,
> readahead thrashing, retried read, and unaligned read. It also adopts the
> data structure introduced by adaptive readahead, parameterizes readahead
> pipelining with `lookahead_index', and reduces the current/ahead windows
> to one single window.
> 
> HEURISTICS
> 
> The logic deals with four cases:
> 
> ...
>

That would have to be the best changelog I've ever seen ;) Thanks for
persisting with this.

> sysbench oltp (trans/sec): up to 8% gain

Have you given any thought to identifying workloads which may be worsened
by your changes?  Attempt to deliberately expose any weak spots?

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