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From: Christoph Hellwig <hch@infradead.org>
To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Jan Kara <jack@suse.cz>, Omar Sandoval <osandov@osandov.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Trond Myklebust <trond.myklebust@primarydata.com>,
	David Sterba <dsterba@suse.cz>,
	linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
	linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/8] swap: lock i_mutex for swap_writepage direct_IO
Date: Tue, 23 Dec 2014 01:37:10 -0800	[thread overview]
Message-ID: <20141223093710.GA29096@infradead.org> (raw)
In-Reply-To: <20141220065133.GC22149@ZenIV.linux.org.uk>

On Sat, Dec 20, 2014 at 06:51:33AM +0000, Al Viro wrote:
> > The problem is that the use of ->direct_IO by the swap code is a gross
> > layering violation.  ->direct_IO is a callback for the filesystem, and
> > the swap code need to call ->read_iter instead of ->readpage and
> > ->write_tier instead of ->direct_IO, and leave the locking to the
> > filesystem.
> 
> The thing is, ->read_iter() and ->write_iter() might decide to fall back to 
> buffered IO path.  XFS is unusual in that respect - there O_DIRECT ends up
> with short write in such case.  Other filesystems, OTOH...

We'll just need a ->swap_activate method that makes sure we really do
direct I/O.  For all filesystems currently suporting swap just checking
that all blocks are allocated (as the ->bmap path already does) should
be enough.

WARNING: multiple messages have this Message-ID (diff)
From: Christoph Hellwig <hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
To: Al Viro <viro-3bDd1+5oDREiFSDQTTA3OLVCufUGDwFn@public.gmane.org>
Cc: Jan Kara <jack-AlSwsSmVLrQ@public.gmane.org>,
	Omar Sandoval <osandov-nWWhXC5lh1RBDgjK7y7TUQ@public.gmane.org>,
	Andrew Morton
	<akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>,
	Trond Myklebust
	<trond.myklebust-7I+n7zu2hftEKMMhf/gKZA@public.gmane.org>,
	David Sterba <dsterba-AlSwsSmVLrQ@public.gmane.org>,
	linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org,
	linux-nfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: [PATCH 2/8] swap: lock i_mutex for swap_writepage direct_IO
Date: Tue, 23 Dec 2014 01:37:10 -0800	[thread overview]
Message-ID: <20141223093710.GA29096@infradead.org> (raw)
In-Reply-To: <20141220065133.GC22149-3bDd1+5oDREiFSDQTTA3OLVCufUGDwFn@public.gmane.org>

On Sat, Dec 20, 2014 at 06:51:33AM +0000, Al Viro wrote:
> > The problem is that the use of ->direct_IO by the swap code is a gross
> > layering violation.  ->direct_IO is a callback for the filesystem, and
> > the swap code need to call ->read_iter instead of ->readpage and
> > ->write_tier instead of ->direct_IO, and leave the locking to the
> > filesystem.
> 
> The thing is, ->read_iter() and ->write_iter() might decide to fall back to 
> buffered IO path.  XFS is unusual in that respect - there O_DIRECT ends up
> with short write in such case.  Other filesystems, OTOH...

We'll just need a ->swap_activate method that makes sure we really do
direct I/O.  For all filesystems currently suporting swap just checking
that all blocks are allocated (as the ->bmap path already does) should
be enough.
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WARNING: multiple messages have this Message-ID (diff)
From: Christoph Hellwig <hch@infradead.org>
To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Jan Kara <jack@suse.cz>, Omar Sandoval <osandov@osandov.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Trond Myklebust <trond.myklebust@primarydata.com>,
	David Sterba <dsterba@suse.cz>,
	linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
	linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/8] swap: lock i_mutex for swap_writepage direct_IO
Date: Tue, 23 Dec 2014 01:37:10 -0800	[thread overview]
Message-ID: <20141223093710.GA29096@infradead.org> (raw)
In-Reply-To: <20141220065133.GC22149@ZenIV.linux.org.uk>

On Sat, Dec 20, 2014 at 06:51:33AM +0000, Al Viro wrote:
> > The problem is that the use of ->direct_IO by the swap code is a gross
> > layering violation.  ->direct_IO is a callback for the filesystem, and
> > the swap code need to call ->read_iter instead of ->readpage and
> > ->write_tier instead of ->direct_IO, and leave the locking to the
> > filesystem.
> 
> The thing is, ->read_iter() and ->write_iter() might decide to fall back to 
> buffered IO path.  XFS is unusual in that respect - there O_DIRECT ends up
> with short write in such case.  Other filesystems, OTOH...

We'll just need a ->swap_activate method that makes sure we really do
direct I/O.  For all filesystems currently suporting swap just checking
that all blocks are allocated (as the ->bmap path already does) should
be enough.

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
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  parent reply	other threads:[~2014-12-23  9:37 UTC|newest]

Thread overview: 63+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-12-15  5:26 [PATCH 0/8] clean up and generalize swap-over-NFS Omar Sandoval
2014-12-15  5:26 ` Omar Sandoval
2014-12-15  5:26 ` [PATCH 1/8] nfs: follow direct I/O write locking convention Omar Sandoval
2014-12-15  5:26   ` Omar Sandoval
2014-12-15 12:49   ` Trond Myklebust
2014-12-15 12:49     ` Trond Myklebust
2014-12-15 15:42     ` Omar Sandoval
2014-12-15 15:42       ` Omar Sandoval
2014-12-15  5:26 ` [PATCH 2/8] swap: lock i_mutex for swap_writepage direct_IO Omar Sandoval
2014-12-15  5:26   ` Omar Sandoval
2014-12-15 16:27   ` Jan Kara
2014-12-15 16:27     ` Jan Kara
2014-12-15 16:56     ` Christoph Hellwig
2014-12-15 16:56       ` Christoph Hellwig
2014-12-15 22:11       ` Omar Sandoval
2014-12-15 22:11         ` Omar Sandoval
2014-12-16  8:35         ` Christoph Hellwig
2014-12-16  8:35           ` Christoph Hellwig
2014-12-16  8:35           ` Christoph Hellwig
2014-12-16  8:56           ` Omar Sandoval
2014-12-16  8:56             ` Omar Sandoval
2014-12-17  8:06             ` Christoph Hellwig
2014-12-17  8:06               ` Christoph Hellwig
2014-12-17  8:20               ` Al Viro
2014-12-17  8:20                 ` Al Viro
2014-12-17  8:24                 ` Christoph Hellwig
2014-12-17  8:24                   ` Christoph Hellwig
2014-12-17 14:58                   ` Omar Sandoval
2014-12-17 14:58                     ` Omar Sandoval
2014-12-17 18:52                     ` Christoph Hellwig
2014-12-17 18:52                       ` Christoph Hellwig
2014-12-17 22:03                       ` Al Viro
2014-12-17 22:03                         ` Al Viro
2014-12-19  6:24                         ` Omar Sandoval
2014-12-19  6:24                           ` Omar Sandoval
2014-12-19  6:28                           ` Al Viro
2014-12-19  6:28                             ` Al Viro
2014-12-19  6:28                             ` Al Viro
2014-12-20  6:51       ` Al Viro
2014-12-20  6:51         ` Al Viro
2014-12-22  7:26         ` Omar Sandoval
2014-12-22  7:26           ` Omar Sandoval
2014-12-23  9:37         ` Christoph Hellwig [this message]
2014-12-23  9:37           ` Christoph Hellwig
2014-12-23  9:37           ` Christoph Hellwig
2014-12-15  5:26 ` [PATCH 3/8] swap: don't add ITER_BVEC flag to direct_IO rw Omar Sandoval
2014-12-15  5:26   ` Omar Sandoval
2014-12-15  6:16   ` Al Viro
2014-12-15  6:16     ` Al Viro
2014-12-15 15:57     ` Omar Sandoval
2014-12-15 15:57       ` Omar Sandoval
2014-12-15  5:26 ` [PATCH 4/8] iov_iter: add iov_iter_bvec and convert callers Omar Sandoval
2014-12-15  5:26   ` Omar Sandoval
2014-12-15  5:26 ` [PATCH 5/8] direct-io: don't dirty ITER_BVEC pages on read Omar Sandoval
2014-12-15  5:26   ` Omar Sandoval
2014-12-15  5:27 ` [PATCH 6/8] nfs: don't dirty ITER_BVEC pages read through direct I/O Omar Sandoval
2014-12-15  5:27   ` Omar Sandoval
2014-12-15  6:17   ` Al Viro
2014-12-15  6:17     ` Al Viro
2014-12-15  5:27 ` [PATCH 7/8] swap: use direct I/O for SWP_FILE swap_readpage Omar Sandoval
2014-12-15  5:27   ` Omar Sandoval
2014-12-15  5:27 ` [PATCH 8/8] vfs: update swap_{,de}activate documentation Omar Sandoval
2014-12-15  5:27   ` Omar Sandoval

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