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

[Andrew Morton <akpm@linux-foundation.org>]

On Thu, 17 May 2007 06:47:57 +0800 Fengguang Wu <wfg@mail.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?