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From: Al Viro <viro@ZenIV.linux.org.uk>
To: Christoph Hellwig <hch@infradead.org>
Cc: Omar Sandoval <osandov@osandov.com>, Jan Kara <jack@suse.cz>,
	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: Wed, 17 Dec 2014 08:20:21 +0000	[thread overview]
Message-ID: <20141217082020.GH22149@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20141217080610.GA20335@infradead.org>

On Wed, Dec 17, 2014 at 12:06:10AM -0800, Christoph Hellwig wrote:

> > This seems to be more or less equivalent to doing a fcntl(F_SETFL) to
> > add the O_DIRECT flag to swap_file (which is a struct file *). Swapoff
> > calls filp_close on swap_file, so I don't see why it's necessary to
> > clear the flag.
> 
> filp_lose doesn't nessecarily destroy the file structure, there might be
> other reference to it, e.g. from dup() or descriptor passing.

Where the hell would those other references come from?  We open the damn
thing in sys_swapon(), never put it into descriptor tables, etc. and
the only reason why we use filp_close() instead of fput() is that we
would miss ->flush() otherwise.

Said that, why not simply *open* it with O_DIRECT to start with and be done
with that?  It's not as if those guys came preopened by caller - swapon(2)
gets a pathname and does opening itself.

WARNING: multiple messages have this Message-ID (diff)
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Christoph Hellwig <hch@infradead.org>
Cc: Omar Sandoval <osandov@osandov.com>, Jan Kara <jack@suse.cz>,
	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: Wed, 17 Dec 2014 08:20:21 +0000	[thread overview]
Message-ID: <20141217082020.GH22149@ZenIV.linux.org.uk> (raw)
In-Reply-To: <20141217080610.GA20335@infradead.org>

On Wed, Dec 17, 2014 at 12:06:10AM -0800, Christoph Hellwig wrote:

> > This seems to be more or less equivalent to doing a fcntl(F_SETFL) to
> > add the O_DIRECT flag to swap_file (which is a struct file *). Swapoff
> > calls filp_close on swap_file, so I don't see why it's necessary to
> > clear the flag.
> 
> filp_lose doesn't nessecarily destroy the file structure, there might be
> other reference to it, e.g. from dup() or descriptor passing.

Where the hell would those other references come from?  We open the damn
thing in sys_swapon(), never put it into descriptor tables, etc. and
the only reason why we use filp_close() instead of fput() is that we
would miss ->flush() otherwise.

Said that, why not simply *open* it with O_DIRECT to start with and be done
with that?  It's not as if those guys came preopened by caller - swapon(2)
gets a pathname and does opening itself.

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  reply	other threads:[~2014-12-17  8:20 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 [this message]
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
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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