Btrfs: avoid taking the chunk_mutex in do_chunk_alloc
Everytime we try to allocate disk space we try and see if we can pre-emptively
allocate a chunk, but in the common case we don't allocate anything, so there is
no sense in taking the chunk_mutex at all. So instead if we are allocating a
chunk, mark it in the space_info so we don't get two people trying to allocate
at the same time. Thanks,
Signed-off-by: Josef Bacik <josef@redhat.com>
Reviewed-by: Liu Bo <liubo2009@cn.fujitsu.com>
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 2647948..31f33ba 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -3039,6 +3039,7 @@
found->bytes_may_use = 0;
found->full = 0;
found->force_alloc = CHUNK_ALLOC_NO_FORCE;
+ found->chunk_alloc = 0;
*space_info = found;
list_add_rcu(&found->list, &info->space_info);
atomic_set(&found->caching_threads, 0);
@@ -3318,10 +3319,9 @@
{
struct btrfs_space_info *space_info;
struct btrfs_fs_info *fs_info = extent_root->fs_info;
+ int wait_for_alloc = 0;
int ret = 0;
- mutex_lock(&fs_info->chunk_mutex);
-
flags = btrfs_reduce_alloc_profile(extent_root, flags);
space_info = __find_space_info(extent_root->fs_info, flags);
@@ -3332,21 +3332,40 @@
}
BUG_ON(!space_info);
+again:
spin_lock(&space_info->lock);
if (space_info->force_alloc)
force = space_info->force_alloc;
if (space_info->full) {
spin_unlock(&space_info->lock);
- goto out;
+ return 0;
}
if (!should_alloc_chunk(extent_root, space_info, alloc_bytes, force)) {
spin_unlock(&space_info->lock);
- goto out;
+ return 0;
+ } else if (space_info->chunk_alloc) {
+ wait_for_alloc = 1;
+ } else {
+ space_info->chunk_alloc = 1;
}
spin_unlock(&space_info->lock);
+ mutex_lock(&fs_info->chunk_mutex);
+
+ /*
+ * The chunk_mutex is held throughout the entirety of a chunk
+ * allocation, so once we've acquired the chunk_mutex we know that the
+ * other guy is done and we need to recheck and see if we should
+ * allocate.
+ */
+ if (wait_for_alloc) {
+ mutex_unlock(&fs_info->chunk_mutex);
+ wait_for_alloc = 0;
+ goto again;
+ }
+
/*
* If we have mixed data/metadata chunks we want to make sure we keep
* allocating mixed chunks instead of individual chunks.
@@ -3372,9 +3391,10 @@
space_info->full = 1;
else
ret = 1;
+
space_info->force_alloc = CHUNK_ALLOC_NO_FORCE;
+ space_info->chunk_alloc = 0;
spin_unlock(&space_info->lock);
-out:
mutex_unlock(&extent_root->fs_info->chunk_mutex);
return ret;
}
