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Re: [RFC 00/11] DAX fsynx/msync support

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [RFC 00/11] DAX fsynx/msync support
From: Jeff Moyer <jmoyer@xxxxxxxxxx>
Date: Wed, 04 Nov 2015 13:34:58 -0500
Cc: linux-nvdimm@xxxxxxxxxxx, "J. Bruce Fields" <bfields@xxxxxxxxxxxx>, linux-mm@xxxxxxxxx, Andreas Dilger <adilger.kernel@xxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, Jeff Layton <jlayton@xxxxxxxxxxxxxxx>, x86@xxxxxxxxxx, Ingo Molnar <mingo@xxxxxxxxxx>, linux-ext4@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, axboe@xxxxxxxxx, "Theodore Ts'o" <tytso@xxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, Jan Kara <jack@xxxxxxxx>, linux-fsdevel@xxxxxxxxxxxxxxx, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Matthew Wilcox <matthew.r.wilcox@xxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <x49twp4p11j.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> (Jeff Moyer's message of "Mon, 02 Nov 2015 16:02:48 -0500")
References: <1446149535-16200-1-git-send-email-ross.zwisler@xxxxxxxxxxxxxxx> <20151030035533.GU19199@dastard> <20151030183938.GC24643@xxxxxxxxxxxxxxx> <20151101232948.GF10656@dastard> <x49vb9kqy5k.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> <20151102201029.GI10656@dastard> <x49twp4p11j.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux)
Jeff Moyer <jmoyer@xxxxxxxxxx> writes:

>> Hence once the filesystem has waited on the REQ_WRITE|REQ_FLUSH IO
>> to complete, we know that all the earlier REQ_WRITE IOs are on
>> stable storage, too. Hence there's no need for the elevator to drain
>> the queue to guarantee completion ordering - the dispatch ordering
>> and flush/fua write semantics guarantee that when the flush/fua
>> completes, all the IOs dispatch prior to that flush/fua write are
>> also on stable storage...
>
> Des xfs rely on this model for correctness?  If so, I'd say we've got a
> problem.

Dave?

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