From: Chris Mason <chris.mason@fusionio.com>
Date: Thu, 31 Jan 2013 19:42:28 +0000 (-0500)
Subject: Btrfs: add a plugging callback to raid56 writes
X-Git-Tag: v3.9-rc1~17^2~28^2~6
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=6ac0f4884eaad28441c6e0f9d1400a08c2149049;p=pandora-kernel.git

Btrfs: add a plugging callback to raid56 writes

Buffered writes and DIRECT_IO writes will often break up
big contiguous changes to the file into sub-stripe writes.

This adds a plugging callback to gather those smaller writes full stripe
writes.

Example on flash:

fio job to do 64K writes in batches of 3 (which makes a full stripe):

With plugging: 450MB/s
Without plugging: 220MB/s

Signed-off-by: Chris Mason <chris.mason@fusionio.com>
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