linux-ext4 - Re: [PATCH v2] iomap: report collisions between directio and buffered writes to userspace

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Message-ID: <20171120202606.GN5858@dastard>
Date:   Tue, 21 Nov 2017 07:26:06 +1100
From:   Dave Chinner <david@...morbit.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     "Darrick J. Wong" <darrick.wong@...cle.com>,
        xfs <linux-xfs@...r.kernel.org>,
        Ilya Dryomov <idryomov@...il.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Brian Foster <bfoster@...hat.com>,
        holger@...lied-asynchrony.com,
        linux-ext4 <linux-ext4@...r.kernel.org>,
        linux-btrfs <linux-btrfs@...r.kernel.org>
Subject: Re: [PATCH v2] iomap: report collisions between directio and
 buffered writes to userspace

On Mon, Nov 20, 2017 at 08:18:29AM -0800, Matthew Wilcox wrote:
> On Fri, Nov 17, 2017 at 11:39:25AM -0800, Darrick J. Wong wrote:
> > If two programs simultaneously try to write to the same part of a file
> > via direct IO and buffered IO, there's a chance that the post-diowrite
> > pagecache invalidation will fail on the dirty page.  When this happens,
> > the dio write succeeded, which means that the page cache is no longer
> > coherent with the disk!
> 
> This seems like a good opportunity to talk about what I've been working
> on for solving this problem.  The XArray is going to introduce a set
> of entries which can be stored to locations in the page cache that I'm
> calling 'wait entries'.

What's this XArray thing you speak of?

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com