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, 4 insertions, 4 deletions

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index a760d97279ac..8a9c76aecdf3 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -188,15 +188,15 @@ int btrfs_drop_extent_cache(struct inode *inode, u64 start, u64 end,
                 if (!split2)
                         split2 = alloc_extent_map(GFP_NOFS);
 
-                spin_lock(&em_tree->lock);
+                write_lock(&em_tree->lock);
                 em = lookup_extent_mapping(em_tree, start, len);
                 if (!em) {
-                        spin_unlock(&em_tree->lock);
+                        write_unlock(&em_tree->lock);
                         break;
                 }
                 flags = em->flags;
                 if (skip_pinned && test_bit(EXTENT_FLAG_PINNED, &em->flags)) {
-                        spin_unlock(&em_tree->lock);
+                        write_unlock(&em_tree->lock);
                         if (em->start <= start &&
                             (!testend || em->start + em->len >= start + len)) {
                                 free_extent_map(em);
@@ -259,7 +259,7 @@ int btrfs_drop_extent_cache(struct inode *inode, u64 start, u64 end,
                         free_extent_map(split);
                         split = NULL;
                 }
-                spin_unlock(&em_tree->lock);
+                write_unlock(&em_tree->lock);
 
                 /* once for us */
                 free_extent_map(em);