ocfs2: increase the default size of local alloc windows

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longer used and the comment above it was out of date.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

View File

@ -75,10 +75,120 @@ static int ocfs2_local_alloc_new_window(struct ocfs2_super *osb,
static int ocfs2_local_alloc_slide_window(struct ocfs2_super *osb,
struct inode *local_alloc_inode);
/*
* ocfs2_la_default_mb() - determine a default size, in megabytes of
* the local alloc.
*
* Generally, we'd like to pick as large a local alloc as
* possible. Performance on large workloads tends to scale
* proportionally to la size. In addition to that, the reservations
* code functions more efficiently as it can reserve more windows for
* write.
*
* Some things work against us when trying to choose a large local alloc:
*
* - We need to ensure our sizing is picked to leave enough space in
* group descriptors for other allocations (such as block groups,
* etc). Picking default sizes which are a multiple of 4 could help
* - block groups are allocated in 2mb and 4mb chunks.
*
* - Likewise, we don't want to starve other nodes of bits on small
* file systems. This can easily be taken care of by limiting our
* default to a reasonable size (256M) on larger cluster sizes.
*
* - Some file systems can't support very large sizes - 4k and 8k in
* particular are limited to less than 128 and 256 megabytes respectively.
*
* The following reference table shows group descriptor and local
* alloc maximums at various cluster sizes (4k blocksize)
*
* csize: 4K group: 126M la: 121M
* csize: 8K group: 252M la: 243M
* csize: 16K group: 504M la: 486M
* csize: 32K group: 1008M la: 972M
* csize: 64K group: 2016M la: 1944M
* csize: 128K group: 4032M la: 3888M
* csize: 256K group: 8064M la: 7776M
* csize: 512K group: 16128M la: 15552M
* csize: 1024K group: 32256M la: 31104M
*/
#define OCFS2_LA_MAX_DEFAULT_MB 256
#define OCFS2_LA_OLD_DEFAULT 8
unsigned int ocfs2_la_default_mb(struct ocfs2_super *osb)
{
unsigned int la_mb;
unsigned int gd_mb;
unsigned int megs_per_slot;
struct super_block *sb = osb->sb;
gd_mb = ocfs2_clusters_to_megabytes(osb->sb,
8 * ocfs2_group_bitmap_size(sb));
/*
* This takes care of files systems with very small group
* descriptors - 512 byte blocksize at cluster sizes lower
* than 16K and also 1k blocksize with 4k cluster size.
*/
if ((sb->s_blocksize == 512 && osb->s_clustersize <= 8192)
|| (sb->s_blocksize == 1024 && osb->s_clustersize == 4096))
return OCFS2_LA_OLD_DEFAULT;
/*
* Leave enough room for some block groups and make the final
* value we work from a multiple of 4.
*/
gd_mb -= 16;
gd_mb &= 0xFFFFFFFB;
la_mb = gd_mb;
/*
* Keep window sizes down to a reasonable default
*/
if (la_mb > OCFS2_LA_MAX_DEFAULT_MB) {
/*
* Some clustersize / blocksize combinations will have
* given us a larger than OCFS2_LA_MAX_DEFAULT_MB
* default size, but get poor distribution when
* limited to exactly 256 megabytes.
*
* As an example, 16K clustersize at 4K blocksize
* gives us a cluster group size of 504M. Paring the
* local alloc size down to 256 however, would give us
* only one window and around 200MB left in the
* cluster group. Instead, find the first size below
* 256 which would give us an even distribution.
*
* Larger cluster group sizes actually work out pretty
* well when pared to 256, so we don't have to do this
* for any group that fits more than two
* OCFS2_LA_MAX_DEFAULT_MB windows.
*/
if (gd_mb > (2 * OCFS2_LA_MAX_DEFAULT_MB))
la_mb = 256;
else {
unsigned int gd_mult = gd_mb;
while (gd_mult > 256)
gd_mult = gd_mult >> 1;
la_mb = gd_mult;
}
}
megs_per_slot = osb->osb_clusters_at_boot / osb->max_slots;
megs_per_slot = ocfs2_clusters_to_megabytes(osb->sb, megs_per_slot);
/* Too many nodes, too few disk clusters. */
if (megs_per_slot < la_mb)
la_mb = megs_per_slot;
return la_mb;
}
void ocfs2_la_set_sizes(struct ocfs2_super *osb, int requested_mb)
{
struct super_block *sb = osb->sb;
unsigned int la_default_mb = OCFS2_DEFAULT_LOCAL_ALLOC_SIZE;
unsigned int la_default_mb = ocfs2_la_default_mb(osb);
unsigned int la_max_mb;
la_max_mb = ocfs2_clusters_to_megabytes(sb,
@ -185,7 +295,7 @@ int ocfs2_load_local_alloc(struct ocfs2_super *osb)
osb->local_alloc_bits, (osb->bitmap_cpg - 1));
osb->local_alloc_bits =
ocfs2_megabytes_to_clusters(osb->sb,
OCFS2_DEFAULT_LOCAL_ALLOC_SIZE);
ocfs2_la_default_mb(osb));
}
/* read the alloc off disk */

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@ -31,6 +31,7 @@ int ocfs2_load_local_alloc(struct ocfs2_super *osb);
void ocfs2_shutdown_local_alloc(struct ocfs2_super *osb);
void ocfs2_la_set_sizes(struct ocfs2_super *osb, int requested_mb);
unsigned int ocfs2_la_default_mb(struct ocfs2_super *osb);
int ocfs2_begin_local_alloc_recovery(struct ocfs2_super *osb,
int node_num,

View File

@ -342,6 +342,9 @@ struct ocfs2_super
*/
unsigned int local_alloc_bits;
unsigned int local_alloc_default_bits;
/* osb_clusters_at_boot can become stale! Do not trust it to
* be up to date. */
unsigned int osb_clusters_at_boot;
enum ocfs2_local_alloc_state local_alloc_state; /* protected
* by osb_lock */

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@ -282,14 +282,6 @@
/* Journal limits (in bytes) */
#define OCFS2_MIN_JOURNAL_SIZE (4 * 1024 * 1024)
/*
* Default local alloc size (in megabytes)
*
* The value chosen should be such that most allocations, including new
* block groups, use local alloc.
*/
#define OCFS2_DEFAULT_LOCAL_ALLOC_SIZE 8
/*
* Inline extended attribute size (in bytes)
* The value chosen should be aligned to 16 byte boundaries.

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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;