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Btrfs: try cluster but don't advance in search list
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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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Alexandre Oliva authored and Chris Mason committed Dec 8, 2011
1 parent 062c05c commit 274bd4f
Showing 1 changed file with 31 additions and 43 deletions.
74 changes: 31 additions & 43 deletions fs/btrfs/extent-tree.c
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Original file line number Diff line number Diff line change
Expand Up @@ -5106,11 +5106,11 @@ static noinline int find_free_extent(struct btrfs_trans_handle *trans,
struct btrfs_root *root = orig_root->fs_info->extent_root;
struct btrfs_free_cluster *last_ptr = NULL;
struct btrfs_block_group_cache *block_group = NULL;
struct btrfs_block_group_cache *used_block_group;
int empty_cluster = 2 * 1024 * 1024;
int allowed_chunk_alloc = 0;
int done_chunk_alloc = 0;
struct btrfs_space_info *space_info;
int last_ptr_loop = 0;
int loop = 0;
int index = 0;
int alloc_type = (data & BTRFS_BLOCK_GROUP_DATA) ?
Expand Down Expand Up @@ -5172,6 +5172,7 @@ static noinline int find_free_extent(struct btrfs_trans_handle *trans,
ideal_cache:
block_group = btrfs_lookup_block_group(root->fs_info,
search_start);
used_block_group = block_group;
/*
* we don't want to use the block group if it doesn't match our
* allocation bits, or if its not cached.
Expand Down Expand Up @@ -5209,6 +5210,7 @@ static noinline int find_free_extent(struct btrfs_trans_handle *trans,
u64 offset;
int cached;

used_block_group = block_group;
btrfs_get_block_group(block_group);
search_start = block_group->key.objectid;

Expand Down Expand Up @@ -5294,49 +5296,33 @@ static noinline int find_free_extent(struct btrfs_trans_handle *trans,
* people trying to start a new cluster
*/
spin_lock(&last_ptr->refill_lock);
if (!last_ptr->block_group ||
last_ptr->block_group->ro ||
!block_group_bits(last_ptr->block_group, data))
used_block_group = last_ptr->block_group;
if (used_block_group != block_group &&
(!used_block_group ||
used_block_group->ro ||
!block_group_bits(used_block_group, data))) {
used_block_group = block_group;
goto refill_cluster;
}

if (used_block_group != block_group)
btrfs_get_block_group(used_block_group);

offset = btrfs_alloc_from_cluster(block_group, last_ptr,
num_bytes, search_start);
offset = btrfs_alloc_from_cluster(used_block_group,
last_ptr, num_bytes, used_block_group->key.objectid);
if (offset) {
/* we have a block, we're done */
spin_unlock(&last_ptr->refill_lock);
goto checks;
}

spin_lock(&last_ptr->lock);
/*
* whoops, this cluster doesn't actually point to
* this block group. Get a ref on the block
* group is does point to and try again
*/
if (!last_ptr_loop && last_ptr->block_group &&
last_ptr->block_group != block_group &&
index <=
get_block_group_index(last_ptr->block_group)) {

btrfs_put_block_group(block_group);
block_group = last_ptr->block_group;
btrfs_get_block_group(block_group);
spin_unlock(&last_ptr->lock);
spin_unlock(&last_ptr->refill_lock);

last_ptr_loop = 1;
search_start = block_group->key.objectid;
/*
* we know this block group is properly
* in the list because
* btrfs_remove_block_group, drops the
* cluster before it removes the block
* group from the list
*/
goto have_block_group;
WARN_ON(last_ptr->block_group != used_block_group);
if (used_block_group != block_group) {
btrfs_put_block_group(used_block_group);
used_block_group = block_group;
}
spin_unlock(&last_ptr->lock);
refill_cluster:
BUG_ON(used_block_group != block_group);
/* If we are on LOOP_NO_EMPTY_SIZE, we can't
* set up a new clusters, so lets just skip it
* and let the allocator find whatever block
Expand All @@ -5357,8 +5343,6 @@ static noinline int find_free_extent(struct btrfs_trans_handle *trans,
*/
btrfs_return_cluster_to_free_space(NULL, last_ptr);

last_ptr_loop = 0;

/* allocate a cluster in this block group */
ret = btrfs_find_space_cluster(trans, root,
block_group, last_ptr,
Expand Down Expand Up @@ -5425,29 +5409,29 @@ static noinline int find_free_extent(struct btrfs_trans_handle *trans,
search_start = stripe_align(root, offset);
/* move on to the next group */
if (search_start + num_bytes >= search_end) {
btrfs_add_free_space(block_group, offset, num_bytes);
btrfs_add_free_space(used_block_group, offset, num_bytes);
goto loop;
}

/* move on to the next group */
if (search_start + num_bytes >
block_group->key.objectid + block_group->key.offset) {
btrfs_add_free_space(block_group, offset, num_bytes);
used_block_group->key.objectid + used_block_group->key.offset) {
btrfs_add_free_space(used_block_group, offset, num_bytes);
goto loop;
}

ins->objectid = search_start;
ins->offset = num_bytes;

if (offset < search_start)
btrfs_add_free_space(block_group, offset,
btrfs_add_free_space(used_block_group, offset,
search_start - offset);
BUG_ON(offset > search_start);

ret = btrfs_update_reserved_bytes(block_group, num_bytes,
ret = btrfs_update_reserved_bytes(used_block_group, num_bytes,
alloc_type);
if (ret == -EAGAIN) {
btrfs_add_free_space(block_group, offset, num_bytes);
btrfs_add_free_space(used_block_group, offset, num_bytes);
goto loop;
}

Expand All @@ -5456,15 +5440,19 @@ static noinline int find_free_extent(struct btrfs_trans_handle *trans,
ins->offset = num_bytes;

if (offset < search_start)
btrfs_add_free_space(block_group, offset,
btrfs_add_free_space(used_block_group, offset,
search_start - offset);
BUG_ON(offset > search_start);
if (used_block_group != block_group)
btrfs_put_block_group(used_block_group);
btrfs_put_block_group(block_group);
break;
loop:
failed_cluster_refill = false;
failed_alloc = false;
BUG_ON(index != get_block_group_index(block_group));
if (used_block_group != block_group)
btrfs_put_block_group(used_block_group);
btrfs_put_block_group(block_group);
}
up_read(&space_info->groups_sem);
Expand Down

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