From 274bd4fb3ed6b72c1d77ef8850511f09fc6b8e4d Mon Sep 17 00:00:00 2001
From: Alexandre Oliva <oliva@lsd.ic.unicamp.br>
Date: Wed, 7 Dec 2011 20:08:40 -0500
Subject: [PATCH] Btrfs: try cluster but don't advance in search list

When we find an existing cluster, we switch to its block group as the
current block group, possibly skipping multiple blocks in the process.
Furthermore, under heavy contention, multiple threads may fail to
allocate from a cluster and then release just-created clusters just to
proceed to create new ones in a different block group.

This patch tries to allocate from an existing cluster regardless of its
block group, and doesn't switch to that group, instead proceeding to
try to allocate a cluster from the group it was iterating before the
attempt.

Signed-off-by: Alexandre Oliva <oliva@lsd.ic.unicamp.br>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
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