Re: [PATCH] fix readahead breakage for sequential after randomreads

[Ram Pai]

Andrew,
	Yes the patch fixes a valid bug.

	
RP

On Mon, 2004-07-26 at 16:29, Andrew Morton wrote:
> Miklos Szeredi <miklos@xxxxxxxxxx> wrote:
> >
> > Current readahead logic is broken when a random read pattern is
> >  followed by a long sequential read.  The cause is that on a window
> >  miss ra->next_size is set to ra->average, but ra->average is only
> >  updated at the end of a sequence, so window size will remain 1 until
> >  the end of the sequential read.
> > 
> >  This patch fixes this by taking the current sequence length into
> >  account (code taken from towards end of page_cache_readahead()), and
> >  also setting ra->average to a decent value in handle_ra_miss() when
> >  sequential access is detected.
> 
> Thanks.   Do you have any performance testing results from this patch?
> 

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