1 files changed, 86 insertions, 23 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index c56f91639dc1..2a4cdceeb575 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -4101,7 +4101,7 @@ wait_block_group_cache_done(struct btrfs_block_group_cache *cache)
 }
 
 enum btrfs_loop_type {
-        LOOP_CACHED_ONLY = 0,
+        LOOP_FIND_IDEAL = 0,
         LOOP_CACHING_NOWAIT = 1,
         LOOP_CACHING_WAIT = 2,
         LOOP_ALLOC_CHUNK = 3,
@@ -4130,12 +4130,15 @@ static noinline int find_free_extent(struct btrfs_trans_handle *trans,
         struct btrfs_block_group_cache *block_group = NULL;
         int empty_cluster = 2 * 1024 * 1024;
         int allowed_chunk_alloc = 0;
+        int done_chunk_alloc = 0;
         struct btrfs_space_info *space_info;
         int last_ptr_loop = 0;
         int loop = 0;
         bool found_uncached_bg = false;
         bool failed_cluster_refill = false;
         bool failed_alloc = false;
+        u64 ideal_cache_percent = 0;
+        u64 ideal_cache_offset = 0;
 
         WARN_ON(num_bytes < root->sectorsize);
         btrfs_set_key_type(ins, BTRFS_EXTENT_ITEM_KEY);
@@ -4171,14 +4174,19 @@ static noinline int find_free_extent(struct btrfs_trans_handle *trans,
                 empty_cluster = 0;
 
         if (search_start == hint_byte) {
+ideal_cache:
                 block_group = btrfs_lookup_block_group(root->fs_info,
                                                        search_start);
                 /*
                  * we don't want to use the block group if it doesn't match our
                  * allocation bits, or if its not cached.
+                 *
+                 * However if we are re-searching with an ideal block group
+                 * picked out then we don't care that the block group is cached.
                  */
                 if (block_group && block_group_bits(block_group, data) &&
-                    block_group_cache_done(block_group)) {
+                    (block_group->cached != BTRFS_CACHE_NO ||
+                     search_start == ideal_cache_offset)) {
                         down_read(&space_info->groups_sem);
                         if (list_empty(&block_group->list) ||
                             block_group->ro) {
@@ -4190,13 +4198,13 @@ static noinline int find_free_extent(struct btrfs_trans_handle *trans,
                                  */
                                 btrfs_put_block_group(block_group);
                                 up_read(&space_info->groups_sem);
-                        } else
+                        } else {
                                 goto have_block_group;
+                        }
                 } else if (block_group) {
                         btrfs_put_block_group(block_group);
                 }
         }
-
 search:
         down_read(&space_info->groups_sem);
         list_for_each_entry(block_group, &space_info->block_groups, list) {
@@ -4208,28 +4216,45 @@ search:
 
 have_block_group:
                 if (unlikely(block_group->cached == BTRFS_CACHE_NO)) {
+                        u64 free_percent;
+
+                        free_percent = btrfs_block_group_used(&block_group->item);
+                        free_percent *= 100;
+                        free_percent = div64_u64(free_percent,
+                                                 block_group->key.offset);
+                        free_percent = 100 - free_percent;
+                        if (free_percent > ideal_cache_percent &&
+                            likely(!block_group->ro)) {
+                                ideal_cache_offset = block_group->key.objectid;
+                                ideal_cache_percent = free_percent;
+                        }
+
                         /*
-                         * we want to start caching kthreads, but not too many
-                         * right off the bat so we don't overwhelm the system,
-                         * so only start them if there are less than 2 and we're
-                         * in the initial allocation phase.
+                         * We only want to start kthread caching if we are at
+                         * the point where we will wait for caching to make
+                         * progress, or if our ideal search is over and we've
+                         * found somebody to start caching.
                          */
                         if (loop > LOOP_CACHING_NOWAIT ||
-                            atomic_read(&space_info->caching_threads) < 2) {
+                            (loop > LOOP_FIND_IDEAL &&
+                             atomic_read(&space_info->caching_threads) < 2)) {
                                 ret = cache_block_group(block_group);
                                 BUG_ON(ret);
                         }
-                }
-
-                cached = block_group_cache_done(block_group);
-                if (unlikely(!cached)) {
                         found_uncached_bg = true;
 
-                        /* if we only want cached bgs, loop */
-                        if (loop == LOOP_CACHED_ONLY)
+                        /*
+                         * If loop is set for cached only, try the next block
+                         * group.
+                         */
+                        if (loop == LOOP_FIND_IDEAL)
                                 goto loop;
                 }
 
+                cached = block_group_cache_done(block_group);
+                if (unlikely(!cached))
+                        found_uncached_bg = true;
+
                 if (unlikely(block_group->ro))
                         goto loop;
 
@@ -4409,9 +4434,11 @@ loop:
         }
         up_read(&space_info->groups_sem);
 
-        /* LOOP_CACHED_ONLY, only search fully cached block groups
-         * LOOP_CACHING_NOWAIT, search partially cached block groups, but
-         *                      dont wait foR them to finish caching
+        /* LOOP_FIND_IDEAL, only search caching/cached bg's, and don't wait for
+         *                      for them to make caching progress.  Also
+         *                      determine the best possible bg to cache
+         * LOOP_CACHING_NOWAIT, search partially cached block groups, kicking
+         *                      caching kthreads as we move along
          * LOOP_CACHING_WAIT, search everything, and wait if our bg is caching
          * LOOP_ALLOC_CHUNK, force a chunk allocation and try again
          * LOOP_NO_EMPTY_SIZE, set empty_size and empty_cluster to 0 and try
@@ -4420,12 +4447,47 @@ loop:
         if (!ins->objectid && loop < LOOP_NO_EMPTY_SIZE &&
             (found_uncached_bg || empty_size || empty_cluster ||
              allowed_chunk_alloc)) {
-                if (found_uncached_bg) {
+                if (loop == LOOP_FIND_IDEAL && found_uncached_bg) {
                         found_uncached_bg = false;
-                        if (loop < LOOP_CACHING_WAIT) {
-                                loop++;
+                        loop++;
+                        if (!ideal_cache_percent &&
+                            atomic_read(&space_info->caching_threads))
                                 goto search;
-                        }
+
+                        /*
+                         * 1 of the following 2 things have happened so far
+                         *
+                         * 1) We found an ideal block group for caching that
+                         * is mostly full and will cache quickly, so we might
+                         * as well wait for it.
+                         *
+                         * 2) We searched for cached only and we didn't find
+                         * anything, and we didn't start any caching kthreads
+                         * either, so chances are we will loop through and
+                         * start a couple caching kthreads, and then come back
+                         * around and just wait for them.  This will be slower
+                         * because we will have 2 caching kthreads reading at
+                         * the same time when we could have just started one
+                         * and waited for it to get far enough to give us an
+                         * allocation, so go ahead and go to the wait caching
+                         * loop.
+                         */
+                        loop = LOOP_CACHING_WAIT;
+                        search_start = ideal_cache_offset;
+                        ideal_cache_percent = 0;
+                        goto ideal_cache;
+                } else if (loop == LOOP_FIND_IDEAL) {
+                        /*
+                         * Didn't find a uncached bg, wait on anything we find
+                         * next.
+                         */
+                        loop = LOOP_CACHING_WAIT;
+                        goto search;
+                }
+
+                if (loop < LOOP_CACHING_WAIT) {
+                        loop++;
+                        goto search;
                 }
 
                 if (loop == LOOP_ALLOC_CHUNK) {
@@ -4437,7 +4499,8 @@ loop:
                         ret = do_chunk_alloc(trans, root, num_bytes +
                                              2 * 1024 * 1024, data, 1);
                         allowed_chunk_alloc = 0;
-                } else {
+                        done_chunk_alloc = 1;
+                } else if (!done_chunk_alloc) {
                         space_info->force_alloc = 1;
                 }