Btrfs: switch extent_map to a rw lock

There are two main users of the extent_map tree.  The
first is regular file inodes, where it is evenly spread
between readers and writers.

The second is the chunk allocation tree, which maps blocks from
logical addresses to phyiscal ones, and it is 99.99% reads.

The mapping tree is a point of lock contention during heavy IO
workloads, so this commit switches things to a rw lock.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 20 insertions, 20 deletions

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index a7e53773e743..d2358c06bbd9 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1749,9 +1749,9 @@ static int btrfs_relocate_chunk(struct btrfs_root *root,
          * step two, delete the device extents and the
          * chunk tree entries
          */
-        spin_lock(&em_tree->lock);
+        read_lock(&em_tree->lock);
         em = lookup_extent_mapping(em_tree, chunk_offset, 1);
-        spin_unlock(&em_tree->lock);
+        read_unlock(&em_tree->lock);
 
         BUG_ON(em->start > chunk_offset ||
                em->start + em->len < chunk_offset);
@@ -1780,9 +1780,9 @@ static int btrfs_relocate_chunk(struct btrfs_root *root,
         ret = btrfs_remove_block_group(trans, extent_root, chunk_offset);
         BUG_ON(ret);
 
-        spin_lock(&em_tree->lock);
+        write_lock(&em_tree->lock);
         remove_extent_mapping(em_tree, em);
-        spin_unlock(&em_tree->lock);
+        write_unlock(&em_tree->lock);
 
         kfree(map);
         em->bdev = NULL;
@@ -2294,9 +2294,9 @@ again:
         em->block_len = em->len;
 
         em_tree = &extent_root->fs_info->mapping_tree.map_tree;
-        spin_lock(&em_tree->lock);
+        write_lock(&em_tree->lock);
         ret = add_extent_mapping(em_tree, em);
-        spin_unlock(&em_tree->lock);
+        write_unlock(&em_tree->lock);
         BUG_ON(ret);
         free_extent_map(em);
 
@@ -2491,9 +2491,9 @@ int btrfs_chunk_readonly(struct btrfs_root *root, u64 chunk_offset)
         int readonly = 0;
         int i;
 
-        spin_lock(&map_tree->map_tree.lock);
+        read_lock(&map_tree->map_tree.lock);
         em = lookup_extent_mapping(&map_tree->map_tree, chunk_offset, 1);
-        spin_unlock(&map_tree->map_tree.lock);
+        read_unlock(&map_tree->map_tree.lock);
         if (!em)
                 return 1;
 
@@ -2518,11 +2518,11 @@ void btrfs_mapping_tree_free(struct btrfs_mapping_tree *tree)
         struct extent_map *em;
 
         while (1) {
-                spin_lock(&tree->map_tree.lock);
+                write_lock(&tree->map_tree.lock);
                 em = lookup_extent_mapping(&tree->map_tree, 0, (u64)-1);
                 if (em)
                         remove_extent_mapping(&tree->map_tree, em);
-                spin_unlock(&tree->map_tree.lock);
+                write_unlock(&tree->map_tree.lock);
                 if (!em)
                         break;
                 kfree(em->bdev);
@@ -2540,9 +2540,9 @@ int btrfs_num_copies(struct btrfs_mapping_tree *map_tree, u64 logical, u64 len)
         struct extent_map_tree *em_tree = &map_tree->map_tree;
         int ret;
 
-        spin_lock(&em_tree->lock);
+        read_lock(&em_tree->lock);
         em = lookup_extent_mapping(em_tree, logical, len);
-        spin_unlock(&em_tree->lock);
+        read_unlock(&em_tree->lock);
         BUG_ON(!em);
 
         BUG_ON(em->start > logical || em->start + em->len < logical);
@@ -2604,9 +2604,9 @@ again:
                 atomic_set(&multi->error, 0);
         }
 
-        spin_lock(&em_tree->lock);
+        read_lock(&em_tree->lock);
         em = lookup_extent_mapping(em_tree, logical, *length);
-        spin_unlock(&em_tree->lock);
+        read_unlock(&em_tree->lock);
 
         if (!em && unplug_page)
                 return 0;
@@ -2763,9 +2763,9 @@ int btrfs_rmap_block(struct btrfs_mapping_tree *map_tree,
         u64 stripe_nr;
         int i, j, nr = 0;
 
-        spin_lock(&em_tree->lock);
+        read_lock(&em_tree->lock);
         em = lookup_extent_mapping(em_tree, chunk_start, 1);
-        spin_unlock(&em_tree->lock);
+        read_unlock(&em_tree->lock);
 
         BUG_ON(!em || em->start != chunk_start);
         map = (struct map_lookup *)em->bdev;
@@ -3053,9 +3053,9 @@ static int read_one_chunk(struct btrfs_root *root, struct btrfs_key *key,
         logical = key->offset;
         length = btrfs_chunk_length(leaf, chunk);
 
-        spin_lock(&map_tree->map_tree.lock);
+        read_lock(&map_tree->map_tree.lock);
         em = lookup_extent_mapping(&map_tree->map_tree, logical, 1);
-        spin_unlock(&map_tree->map_tree.lock);
+        read_unlock(&map_tree->map_tree.lock);
 
         /* already mapped? */
         if (em && em->start <= logical && em->start + em->len > logical) {
@@ -3114,9 +3114,9 @@ static int read_one_chunk(struct btrfs_root *root, struct btrfs_key *key,
                 map->stripes[i].dev->in_fs_metadata = 1;
         }
 
-        spin_lock(&map_tree->map_tree.lock);
+        write_lock(&map_tree->map_tree.lock);
         ret = add_extent_mapping(&map_tree->map_tree, em);
-        spin_unlock(&map_tree->map_tree.lock);
+        write_unlock(&map_tree->map_tree.lock);
         BUG_ON(ret);
         free_extent_map(em);