From: Dmitry Monakhov <dmonakhov@openvz.org>
Date: Thu, 28 Oct 2010 02:08:46 +0000 (-0400)
Subject: ext4: optimize orphan_list handling for ext4_setattr
X-Git-Tag: v2.6.37-rc1~76^2^2~1
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=3d287de3b828226e5a450c7fd5bf4283792dc2b0;p=pandora-kernel.git

ext4: optimize orphan_list handling for ext4_setattr

Surprisingly chown() on ext4 is not SMP scalable operation.
Due to unconditional orphan_del(NULL, inode) in ext4_setattr()
result in significant performance overhead because of global orphan
mutex, especially in no-journal mode (where orphan_add() is noop).
It is possible to skip explicit orphan_del if possible.
Results of fchown() micro-benchmark in no-journal mode
while (1) {
   iteration++;
   fchown(fd, uid, gid);
   fchown(fd, uid + 1, gid + 1)
}
measured: iterations per millisecond
| nr_tasks | w/o patch | with patch |
|        1 |       142 |        185 |
|        4 |       109 |        642 |

Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
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