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Date: Tue, 27 Nov 2001 18:48:18 -0800
From: Andrew Morton <akpm@zip.com.au>
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To: Mike Fedyk <mfedyk@matchmail.com>
CC: Dieter N?tzel <Dieter.Nuetzel@hamburg.de>,
        Linux Kernel List <linux-kernel@vger.kernel.org>
Subject: Re: Unresponiveness of 2.4.16
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Mike Fedyk wrote:
> 
> >       echo file_readahead:N > /proc/ide/ide0/hda/settings
> >
> > where N is in kilobytes in 2.4.16 kernels.
> 
> Any idea which drivers it will/won't work on?  ie, "almost all ide" or
> "almost none of the ide driers"?

It appears that all IDE is controlled with /proc/ide/ide0/hda/settings

> >In earlier kernels
> > it's kilopages (!).
> 
> Isn't this part of the max-readahead patch?

No, that fix went in separately.  Roger Larsson created it, then
I hit the same problem and forwarded Roger's patch to the relevant
parties.
 
> Does /proc/sys/vm/max_readahead affect scsi in any way?

Well, `grep -r max_readahead drivers/scsi' comes up blank,
so it looks like the scsi drivers don't implement the
driver-specific readhead tunable, and so they will fall back
to the /proc/sys/vm/max_readahead global.  I guess.

> What layer does /proc/sys/vm/max_readahead affect?  Block? FS?

The generic filesystem library code.  The bit which sits
on top of the block layer and gets its block mappings from the
filesystem and does generic_file_readahead().  Variously
referred to as VFS or VM.  It's neither, and both, really.
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