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Date: Fri, 27 Mar 2015 01:48:33 -0700
From: Christoph Hellwig <hch@infradead.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Christoph Hellwig <hch@infradead.org>, Milosz Tanski <milosz@adfin.com>,
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        Dave Chinner <david@fromorbit.com>
Subject: Re: [PATCH v7 0/5] vfs: Non-blockling buffered fs read (page cache
 only)
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On Fri, Mar 27, 2015 at 01:35:16AM -0700, Andrew Morton wrote:
> fincore() doesn't have to be ugly.  Please address the design issues I
> raised.  How is pread2() useful to the class of applications which
> cannot proceed until all data is available?

It actually makes them work correctly?  preadv2( ..., DONTWAIT) will
return -EGAIN, which causes them to bounce to the threadpool where
they call preadv(...).