Btrfs: don't pre-allocate btrfs bio

We pre-allocate a btrfs bio with fixed size, and then may re-allocate
memory if we find stripes are bigger than the fixed size. But this
pre-allocation is not necessary.

Also we don't have to calcuate the stripe number twice.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>

1 files changed, 21 insertions, 46 deletions

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 73f673c8d8d8..540fdd25fb5e 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -2897,26 +2897,13 @@ static int __btrfs_map_block(struct btrfs_mapping_tree *map_tree, int rw,
         u64 stripe_nr;
         u64 stripe_nr_orig;
         u64 stripe_nr_end;
-        int stripes_allocated = 8;
-        int stripes_required = 1;
         int stripe_index;
         int i;
+        int ret = 0;
         int num_stripes;
         int max_errors = 0;
         struct btrfs_bio *bbio = NULL;
 
-        if (bbio_ret && !(rw & (REQ_WRITE | REQ_DISCARD)))
-                stripes_allocated = 1;
-again:
-        if (bbio_ret) {
-                bbio = kzalloc(btrfs_bio_size(stripes_allocated),
-                                GFP_NOFS);
-                if (!bbio)
-                        return -ENOMEM;
-
-                atomic_set(&bbio->error, 0);
-        }
-
         read_lock(&em_tree->lock);
         em = lookup_extent_mapping(em_tree, logical, *length);
         read_unlock(&em_tree->lock);
@@ -2935,32 +2922,6 @@ again:
         if (mirror_num > map->num_stripes)
                 mirror_num = 0;
 
-        /* if our btrfs_bio struct is too small, back off and try again */
-        if (rw & REQ_WRITE) {
-                if (map->type & (BTRFS_BLOCK_GROUP_RAID1 |
-                                 BTRFS_BLOCK_GROUP_DUP)) {
-                        stripes_required = map->num_stripes;
-                        max_errors = 1;
-                } else if (map->type & BTRFS_BLOCK_GROUP_RAID10) {
-                        stripes_required = map->sub_stripes;
-                        max_errors = 1;
-                }
-        }
-        if (rw & REQ_DISCARD) {
-                if (map->type & (BTRFS_BLOCK_GROUP_RAID0 |
-                                 BTRFS_BLOCK_GROUP_RAID1 |
-                                 BTRFS_BLOCK_GROUP_DUP |
-                                 BTRFS_BLOCK_GROUP_RAID10)) {
-                        stripes_required = map->num_stripes;
-                }
-        }
-        if (bbio_ret && (rw & (REQ_WRITE | REQ_DISCARD)) &&
-            stripes_allocated < stripes_required) {
-                stripes_allocated = map->num_stripes;
-                free_extent_map(em);
-                kfree(bbio);
-                goto again;
-        }
         stripe_nr = offset;
         /*
          * stripe_nr counts the total number of stripes we have to stride
@@ -3055,6 +3016,13 @@ again:
         }
         BUG_ON(stripe_index >= map->num_stripes);
 
+        bbio = kzalloc(btrfs_bio_size(num_stripes), GFP_NOFS);
+        if (!bbio) {
+                ret = -ENOMEM;
+                goto out;
+        }
+        atomic_set(&bbio->error, 0);
+
         if (rw & REQ_DISCARD) {
                 for (i = 0; i < num_stripes; i++) {
                         bbio->stripes[i].physical =
@@ -3151,15 +3119,22 @@ again:
                         stripe_index++;
                 }
         }
-        if (bbio_ret) {
-                *bbio_ret = bbio;
-                bbio->num_stripes = num_stripes;
-                bbio->max_errors = max_errors;
-                bbio->mirror_num = mirror_num;
+
+        if (rw & REQ_WRITE) {
+                if (map->type & (BTRFS_BLOCK_GROUP_RAID1 |
+                                 BTRFS_BLOCK_GROUP_RAID10 |
+                                 BTRFS_BLOCK_GROUP_DUP)) {
+                        max_errors = 1;
+                }
         }
+
+        *bbio_ret = bbio;
+        bbio->num_stripes = num_stripes;
+        bbio->max_errors = max_errors;
+        bbio->mirror_num = mirror_num;
 out:
         free_extent_map(em);
-        return 0;
+        return ret;
 }
 
 int btrfs_map_block(struct btrfs_mapping_tree *map_tree, int rw,