From: Chris Mason <chris.mason@oracle.com>
Date: Mon, 18 May 2009 14:41:58 +0000 (-0400)
Subject: Btrfs: reduce mount -o ssd CPU usage
X-Git-Tag: v2.6.31-rc1~380^2~18
X-Git-Url: http://bbs.cooldavid.org/git/?a=commitdiff_plain;h=2c943de6ad795a174dcc424c293bb77f15ae3b8c;p=net-next-2.6.git

Btrfs: reduce mount -o ssd CPU usage

The block allocator in SSD mode will try to find groups of free blocks
that are close together.  This commit makes it loop less on a given
group size before bumping it.

The end result is that we are less likely to fill small holes in the
available free space, but we don't waste as much CPU building the
large cluster used by ssd mode.

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

diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
index 0bc93657b46..280165581c5 100644
--- a/fs/btrfs/free-space-cache.c
+++ b/fs/btrfs/free-space-cache.c
@@ -652,7 +652,7 @@ again:
 			last = entry;
 			max_extent = 0;
 			total_retries++;
-			if (total_retries % 256 == 0) {
+			if (total_retries % 64 == 0) {
 				if (min_bytes >= (bytes + empty_size)) {
 					ret = -ENOSPC;
 					goto out;