From 7a26285eea8eb92e0088db011571d887d4551b0f Mon Sep 17 00:00:00 2001
From: Arne Jansen <sensille@gmx.net>
Date: Fri, 10 Jun 2011 12:39:23 +0200
Subject: [PATCH] btrfs: use readahead API for scrub

Scrub uses a simple tree-enumeration to bring the relevant portions
of the extent- and csum-tree into the page cache before starting the
scrub-I/O. This is now replaced by using the new readahead-API.
During readahead the scrub is being accounted as paused, so it won't
hold off transaction commits.

This change raises the average disk bandwith utilisation on my test
volume from 70% to 90%. On another volume, the time for a test run
went down from 89s to 43s.

Changes v5:
 - reada1/2 are now of type struct reada_control *

Signed-off-by: Arne Jansen <sensille@gmx.net>
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