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Date: Thu, 7 Aug 2003 10:39:30 -0700
From: Andrew Morton <akpm@osdl.org>
To: Badari Pulavarty <pbadari@us.ibm.com>
Cc: suparna@in.ibm.com, linux-kernel@vger.kernel.org, linux-aio@kvack.org
Subject: Re: [PATCH][2.6-mm] Readahead issues and AIO read speedup
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Badari Pulavarty <pbadari@us.ibm.com> wrote:
>
> We should do readahead of actual pages required by the current 
> read would be correct solution. (like Suparna suggested).

I repeat: what will be the effect of this if all those pages are already in
pagecache?

> When readahead window is closed,  slow read code will be submitting IO in 4k 
> chunks. Infact, it will wait for the IO to finish, before reading next page. 
> Isn't it?

Yes.

> How would you ensure atleast 16k worth of pages are submitted
> in a sinle chunk here ?

Need to work out why the window got itself shrunk, fix that, then constrain each
readahead chunk to the size of the application's read() if the application
just seeked, I think.

> I am hoping that forcing readhead code to read pages needed by current read 
> would address this problem.

You'll have Martin and Anton coming after you with SDET regressions.