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ocfs2: increase the default size of local alloc windows

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I have observed that the current size of 8M gives us pretty poor
fragmentation on multi-threaded workloads which do lots of writes.

Generally, I can increase the size of local alloc windows and observe a
marked decrease in fragmentation, even up and beyond window sizes of 512
megabytes. This makes sense for a couple reasons - larger local alloc means
more room for reservation windows. On multi-node workloads the larger local
alloc helps as well because we don't have to do window slides as often.

Also, I removed the OCFS2_DEFAULT_LOCAL_ALLOC_SIZE constant as it is no
longer used and the comment above it was out of date.

To test fragmentation, I used a workload which launched 4 threads that did
4k writes into a series of about 140 alternating files.

With resv_level=2, and a 4k/4k file system I observed the following average
fragmentation for various localalloc= parameters:

localalloc=	avg. fragmentation
	8		48
	32		16
	64		10
	120		7

On larger cluster sizes, the difference is more dramatic.

The new default size top out at 256M, which we'll only get for cluster
sizes of 32K and above.

Signed-off-by: Mark Fasheh <mfasheh@suse.com>
Signed-off-by: Joel Becker <joel.becker@oracle.com>
This commit is contained in:
Mark Fasheh
2010-04-05 18:17:14 -07:00
committed by Joel Becker
parent 73c8a80003
commit 6b82021b9e
5 changed files with 118 additions and 11 deletions
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3
fs/ocfs2/super.c
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@@ -1503,7 +1503,7 @@ static int ocfs2_show_options(struct seq_file *s, struct vfsmount *mnt)
(unsigned) (osb->osb_commit_interval / HZ));
local_alloc_megs = osb->local_alloc_bits >> (20 - osb->s_clustersize_bits);
if (local_alloc_megs != OCFS2_DEFAULT_LOCAL_ALLOC_SIZE)
if (local_alloc_megs != ocfs2_la_default_mb(osb))
seq_printf(s, ",localalloc=%d", local_alloc_megs);
if (opts & OCFS2_MOUNT_LOCALFLOCKS)
@@ -2251,6 +2251,7 @@ static int ocfs2_initialize_super(struct super_block *sb,
}
osb->bitmap_blkno = OCFS2_I(inode)->ip_blkno;
osb->osb_clusters_at_boot = OCFS2_I(inode)->ip_clusters;
iput(inode);
osb->bitmap_cpg = ocfs2_group_bitmap_size(sb) * 8;