From: Christoph Hellwig <hch@infradead.org>
Date: Sun, 18 Dec 2011 20:00:09 +0000 (+0000)
Subject: xfs: replace i_flock with a sleeping bitlock
X-Git-Tag: v3.3-rc1~24^2~5
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=474fce067521a40dbacc722e8ba119e81c2d31bf;p=pandora-kernel.git

xfs: replace i_flock with a sleeping bitlock

We almost never block on i_flock, the exception is synchronous inode
flushing.  Instead of bloating the inode with a 16/24-byte completion
that we abuse as a semaphore just implement it as a bitlock that uses
a bit waitqueue for the rare sleeping path.  This primarily is a
tradeoff between a much smaller inode and a faster non-blocking
path vs faster wakeups, and we are much better off with the former.

A small downside is that we will lose lockdep checking for i_flock, but
given that it's always taken inside the ilock that should be acceptable.

Note that for example the inode writeback locking is implemented in a
very similar way.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Alex Elder <aelder@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
---

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