From: Theodore Ts'o <tytso@mit.edu>
To: Christoph Hellwig <hch@infradead.org>
Cc: Hugh Dickins <hughd@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
Al Viro <viro@zeniv.linux.org.uk>,
bugzilla-daemon@bugzilla.kernel.org, meetmehiro@gmail.com,
linux-mm@kvack.org, linux-fsdevel@vger.kernel.org
Subject: Re: [Bug 50981] generic_file_aio_read ?: No locking means DATA CORRUPTION read and write on same 4096 page range
Date: Mon, 26 Nov 2012 20:32:54 -0500 [thread overview]
Message-ID: <20121127013254.GA25222@thunk.org> (raw)
In-Reply-To: <20121126220908.GA20733@infradead.org>
On Mon, Nov 26, 2012 at 05:09:08PM -0500, Christoph Hellwig wrote:
> On Mon, Nov 26, 2012 at 04:49:37PM -0500, Theodore Ts'o wrote:
> > Christoph, can you give some kind of estimate for the overhead that
> > adding this locking in XFS actually costs in practice?
>
> I don't know any real life measurements, but in terms of implementation
> the over head is:
>
> a) taking a the rw_semaphore in shared mode for every buffered read
> b) taking the slightly slower exclusive rw_semaphore for buffered writes
> instead of the plain mutex
>
> On the other hand it significantly simplifies the locking for direct
> I/O and allows parallel direct I/O writers.
I should probably just look at the XFS code, but.... if you're taking
an exclusve lock for buffered writes, won't this impact the
performance of buffered writes happening in parallel on different
CPU's?
- Ted
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next prev parent reply other threads:[~2012-11-27 1:32 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <bug-50981-5823@https.bugzilla.kernel.org/>
[not found] ` <20121126163328.ACEB011FE9C@bugzilla.kernel.org>
2012-11-26 16:45 ` [Bug 50981] generic_file_aio_read ?: No locking means DATA CORRUPTION read and write on same 4096 page range Theodore Ts'o
2012-11-26 18:59 ` Hiro Lalwani
2012-11-26 20:05 ` Hugh Dickins
2012-11-26 20:13 ` Christoph Hellwig
2012-11-26 21:28 ` Dave Chinner
2012-11-26 21:39 ` Christoph Hellwig
2012-11-26 21:49 ` Theodore Ts'o
2012-11-26 22:09 ` Christoph Hellwig
2012-11-27 1:32 ` Theodore Ts'o [this message]
2012-11-27 4:27 ` Dave Chinner
2012-11-26 22:17 ` Dave Chinner
2012-11-26 20:15 ` Zach Brown
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