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Date: Mon, 26 Sep 2005 21:24:46 -0700
From: Andrew Morton <akpm@osdl.org>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: linux-kernel@vger.kernel.org
Subject: Re: Readahead
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Alan Stern <stern@rowland.harvard.edu> wrote:
>
>  Can somebody please tell me where the code is that performs optimistic
>  readahead when a process does sequential reads on a block device?

mm/readahead.c:__do_page_cache_readahead() is the main one.  Use
dump_stack() to be sure.

>  And can someone explain why those readahead calls are allowed to extend 
>  beyond the end of the device?

It has a check in there for reads past the blockdev mapping's i_size. 
Maybe i_size is wrong, or maybe the code is wrong, or maybe it's a
different caller.