So I'm trying to figure out what it is that makes clustered allocation
so much faster than unclustered allocation. E.g., for a nearly
quiescent filesystem with as little as 90MB of metadata, balance-md
(from another patch I posted today) takes some 4.5 seconds (worst case
6s, best case 4s) with clustered allocation, while with -o nocluster it
takes some 6.5s (best case 6s, worst case 7s). With -o mincluster,
introduced by the patch below (by no means intended for merging, it's
far too hackish) it's some 0.1s faster than with -o nocluster, but
nothing really significant, and I didn't even take care of locking
last_ptr. So I conclude it's not remembering the search starting point
that makes -o cluster faster.
Anyhow, since this is slightly faster than unclustered allocation, I
suppose we could introduce something along these lines for the -o
nocluster case, no?
>From c16a9e53e41e7616e4498534eea25ca1f396d7b4 Mon Sep 17 00:00:00 2001
From: Alexandre Oliva <lxoliva@xxxxxxxxx>
Date: Thu, 10 Nov 2011 20:55:40 -0200
Subject: [PATCH 9/9] Add -o mincluster option.
If this option is enabled, save the location of the last successful
allocation, so as to emulate some of the cluster allocation logic
(though not non-bitmap preference) without actually going through the
exercise of allocating clusters.
Signed-off-by: Alexandre Oliva <oliva@xxxxxxxxxxxxxxxxx>
---
fs/btrfs/extent-tree.c | 16 +++++++++++++---
fs/btrfs/free-space-cache.c | 1 +
fs/btrfs/super.c | 17 +++++++++++++----
3 files changed, 27 insertions(+), 7 deletions(-)
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 4da27be..caa73b2 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -5053,7 +5053,7 @@ static noinline int find_free_extent(struct btrfs_trans_handle *trans,
{
int ret = 0;
struct btrfs_root *root = orig_root->fs_info->extent_root;
- struct btrfs_free_cluster *last_ptr = NULL;
+ struct btrfs_free_cluster *last_ptr = NULL, *save_ptr = NULL;
struct btrfs_block_group_cache *block_group = NULL;
int empty_cluster = 2 * 1024 * 1024;
int allowed_chunk_alloc = 0;
@@ -5095,8 +5095,16 @@ static noinline int find_free_extent(struct btrfs_trans_handle *trans,
if (data & BTRFS_BLOCK_GROUP_METADATA && use_cluster) {
last_ptr = &root->fs_info->meta_alloc_cluster;
- if (!btrfs_test_opt(root, SSD))
- empty_cluster = 64 * 1024;
+ if (!btrfs_test_opt(root, SSD)) {
+ /* !SSD && SSD_SPREAD == -o mincluster. */
+ if (btrfs_test_opt(root, SSD_SPREAD)) {
+ save_ptr = last_ptr;
+ hint_byte = save_ptr->window_start;
+ last_ptr = NULL;
+ use_cluster = false;
+ } else
+ empty_cluster = 64 * 1024;
+ }
}
if ((data & BTRFS_BLOCK_GROUP_DATA) && use_cluster &&
@@ -5402,6 +5410,8 @@ checks:
btrfs_add_free_space(block_group, offset,
search_start - offset);
BUG_ON(offset > search_start);
+ if (save_ptr)
+ save_ptr->window_start = search_start + num_bytes;
btrfs_put_block_group(block_group);
break;
loop:
diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
index afd1129..2706369 100644
--- a/fs/btrfs/free-space-cache.c
+++ b/fs/btrfs/free-space-cache.c
@@ -2576,6 +2576,7 @@ void btrfs_init_free_cluster(struct btrfs_free_cluster *cluster)
cluster->max_size = 0;
INIT_LIST_HEAD(&cluster->block_group_list);
cluster->block_group = NULL;
+ cluster->window_start = 0;
}
int btrfs_trim_block_group(struct btrfs_block_group_cache *block_group,
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 2baba99..dd76fa4 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -165,7 +165,7 @@ enum {
Opt_space_cache, Opt_clear_cache, Opt_user_subvol_rm_allowed,
Opt_enospc_debug, Opt_subvolrootid, Opt_defrag,
Opt_inode_cache, Opt_no_space_cache, Opt_recovery,
- Opt_nocluster, Opt_cluster, Opt_err,
+ Opt_nocluster, Opt_cluster, Opt_mincluster, Opt_err,
};
static match_table_t tokens = {
@@ -202,6 +202,7 @@ static match_table_t tokens = {
{Opt_recovery, "recovery"},
{Opt_nocluster, "nocluster"},
{Opt_cluster, "cluster"},
+ {Opt_mincluster, "mincluster"},
{Opt_err, NULL},
};
@@ -407,6 +408,11 @@ int btrfs_parse_options(struct btrfs_root *root, char *options)
printk(KERN_INFO "btrfs: enabling alloc clustering\n");
btrfs_clear_opt(info->mount_opt, NO_ALLOC_CLUSTER);
break;
+ case Opt_mincluster:
+ printk(KERN_INFO "btrfs: enabling minimal alloc clustering\n");
+ btrfs_clear_opt(info->mount_opt, NO_ALLOC_CLUSTER);
+ btrfs_set_opt(info->mount_opt, SSD_SPREAD);
+ break;
case Opt_err:
printk(KERN_INFO "btrfs: unrecognized mount option "
"'%s'\n", p);
@@ -705,9 +711,12 @@ static int btrfs_show_options(struct seq_file *seq, struct vfsmount *vfs)
}
if (btrfs_test_opt(root, NOSSD))
seq_puts(seq, ",nossd");
- if (btrfs_test_opt(root, SSD_SPREAD))
- seq_puts(seq, ",ssd_spread");
- else if (btrfs_test_opt(root, SSD))
+ if (btrfs_test_opt(root, SSD_SPREAD)) {
+ if (btrfs_test_opt(root, SSD))
+ seq_puts(seq, ",ssd_spread");
+ else
+ seq_puts(seq, ",mincluster");
+ } else if (btrfs_test_opt(root, SSD))
seq_puts(seq, ",ssd");
if (btrfs_test_opt(root, NOTREELOG))
seq_puts(seq, ",notreelog");
--
1.7.4.4
--
Alexandre Oliva, freedom fighter http://FSFLA.org/~lxoliva/
You must be the change you wish to see in the world. -- Gandhi
Be Free! -- http://FSFLA.org/ FSF Latin America board member
Free Software Evangelist Red Hat Brazil Compiler Engineer
