Date: Thu, 25 Oct 2012 10:38:08 +0800
From: Fengguang Wu <fengguang.wu@intel.com>
To: YingHang Zhu <casualfisher@gmail.com>
Cc: Dave Chinner <david@fromorbit.com>, akpm@linux-foundation.org,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [PATCH] mm: readahead: remove redundant ra_pages in file_ra_state
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Hi YingHang,

> Actually I've talked about it with Fengguang, he advised we should unify the
> ra_pages in struct bdi and file_ra_state and leave the issue that
> spreading data
> across disks as it is.
> Fengguang, what's you opinion about this?

Yeah the two ra_pages may run out of sync for already opened files,
which could be a problem for long opened files. However as Dave put
it, a device's max readahead size is typically a static value that can
be set at mount time. So, the question is: do you really hurt from the
old behavior that deserves this code change?

I agree with Dave that the multi-disk case is not a valid concern.  In
fact, how can the patch help that case? I mean, if it's two fuse files
lying in two disks, it *was* not a problem at all. If it's one big
file spreading to two disks, it's a too complex scheme to be
practically manageable which I doubt if you have such a setup. 

Thanks,
Fengguang
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