Btrfs: reuse the extent_map we found when calling btrfs_get_extent

In btrfs_get_block_direct we call btrfs_get_extent to lookup the extent for the
range that we are looking for.  If we don't find an extent, btrfs_get_extent
will insert a extent_map for that area and mark it as a hole.  So it does the
job of allocating a new extent map and inserting it into the io tree.  But if
we're creating a new extent we free it up and redo all of that work.  So instead
pass the em to btrfs_new_extent_direct(), and if it will work just allocate the
disk space and set it up properly and bypass the freeing/allocating of a new
extent map and the expensive operation of inserting the thing into the io_tree.
Thanks,

Signed-off-by: Josef Bacik <josef@redhat.com>

1 files changed, 28 insertions, 8 deletions

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 2bb76c6157a4..24310c9cb14f 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -5445,17 +5445,30 @@ out:
 }
 
 static struct extent_map *btrfs_new_extent_direct(struct inode *inode,
+                                                  struct extent_map *em,
                                                   u64 start, u64 len)
 {
         struct btrfs_root *root = BTRFS_I(inode)->root;
         struct btrfs_trans_handle *trans;
-        struct extent_map *em;
         struct extent_map_tree *em_tree = &BTRFS_I(inode)->extent_tree;
         struct btrfs_key ins;
         u64 alloc_hint;
         int ret;
+        bool insert = false;
 
-        btrfs_drop_extent_cache(inode, start, start + len - 1, 0);
+        /*
+         * Ok if the extent map we looked up is a hole and is for the exact
+         * range we want, there is no reason to allocate a new one, however if
+         * it is not right then we need to free this one and drop the cache for
+         * our range.
+         */
+        if (em->block_start != EXTENT_MAP_HOLE || em->start != start ||
+            em->len != len) {
+                free_extent_map(em);
+                em = NULL;
+                insert = true;
+                btrfs_drop_extent_cache(inode, start, start + len - 1, 0);
+        }
 
         trans = btrfs_join_transaction(root, 0);
         if (IS_ERR(trans))
@@ -5471,10 +5484,12 @@ static struct extent_map *btrfs_new_extent_direct(struct inode *inode,
                 goto out;
         }
 
-        em = alloc_extent_map(GFP_NOFS);
         if (!em) {
-                em = ERR_PTR(-ENOMEM);
-                goto out;
+                em = alloc_extent_map(GFP_NOFS);
+                if (!em) {
+                        em = ERR_PTR(-ENOMEM);
+                        goto out;
+                }
         }
 
         em->start = start;
@@ -5484,9 +5499,15 @@ static struct extent_map *btrfs_new_extent_direct(struct inode *inode,
         em->block_start = ins.objectid;
         em->block_len = ins.offset;
         em->bdev = root->fs_info->fs_devices->latest_bdev;
+
+        /*
+         * We need to do this because if we're using the original em we searched
+         * for, we could have EXTENT_FLAG_VACANCY set, and we don't want that.
+         */
+        em->flags = 0;
         set_bit(EXTENT_FLAG_PINNED, &em->flags);
 
-        while (1) {
+        while (insert) {
                 write_lock(&em_tree->lock);
                 ret = add_extent_mapping(em_tree, em);
                 write_unlock(&em_tree->lock);
@@ -5704,8 +5725,7 @@ must_cow:
          * it above
          */
         len = bh_result->b_size;
-        free_extent_map(em);
-        em = btrfs_new_extent_direct(inode, start, len);
+        em = btrfs_new_extent_direct(inode, em, start, len);
         if (IS_ERR(em))
                 return PTR_ERR(em);
         len = min(len, em->len - (start - em->start));