1 files changed, 21 insertions, 14 deletions

diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
index 4eb296426061..5c2caad76212 100644
--- a/fs/btrfs/free-space-cache.c
+++ b/fs/btrfs/free-space-cache.c
@@ -259,7 +259,9 @@ static int link_free_space(struct btrfs_block_group_cache *block_group,
 
 static void recalculate_thresholds(struct btrfs_block_group_cache *block_group)
 {
-        u64 max_bytes, possible_bytes;
+        u64 max_bytes;
+        u64 bitmap_bytes;
+        u64 extent_bytes;
 
         /*
          * The goal is to keep the total amount of memory used per 1gb of space
@@ -269,22 +271,27 @@ static void recalculate_thresholds(struct btrfs_block_group_cache *block_group)
         max_bytes = MAX_CACHE_BYTES_PER_GIG *
                 (div64_u64(block_group->key.offset, 1024 * 1024 * 1024));
 
-        possible_bytes = (block_group->total_bitmaps * PAGE_CACHE_SIZE) +
-                (sizeof(struct btrfs_free_space) *
-                 block_group->extents_thresh);
+        /*
+         * we want to account for 1 more bitmap than what we have so we can make
+         * sure we don't go over our overall goal of MAX_CACHE_BYTES_PER_GIG as
+         * we add more bitmaps.
+         */
+        bitmap_bytes = (block_group->total_bitmaps + 1) * PAGE_CACHE_SIZE;
 
-        if (possible_bytes > max_bytes) {
-                int extent_bytes = max_bytes -
-                        (block_group->total_bitmaps * PAGE_CACHE_SIZE);
+        if (bitmap_bytes >= max_bytes) {
+                block_group->extents_thresh = 0;
+                return;
+        }
 
-                if (extent_bytes <= 0) {
-                        block_group->extents_thresh = 0;
-                        return;
-                }
+        /*
+         * we want the extent entry threshold to always be at most 1/2 the maxw
+         * bytes we can have, or whatever is less than that.
+         */
+        extent_bytes = max_bytes - bitmap_bytes;
+        extent_bytes = min_t(u64, extent_bytes, div64_u64(max_bytes, 2));
 
-                block_group->extents_thresh = extent_bytes /
-                        (sizeof(struct btrfs_free_space));
-        }
+        block_group->extents_thresh =
+                div64_u64(extent_bytes, (sizeof(struct btrfs_free_space)));
 }
 
 static void bitmap_clear_bits(struct btrfs_block_group_cache *block_group,