ext4: Use atomic_t's in struct flex_groups

Reduce pressure on the sb_bgl_lock family of locks by using atomic_t's
to track the number of free blocks and inodes in each flex_group.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 15 insertions, 18 deletions

diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
index 617f5a2d800a..5f393927fd25 100644
--- a/fs/ext4/ialloc.c
+++ b/fs/ext4/ialloc.c
@@ -189,7 +189,6 @@ void ext4_free_inode(handle_t *handle, struct inode *inode)
         struct ext4_super_block *es;
         struct ext4_sb_info *sbi;
         int fatal = 0, err, count, cleared;
-        ext4_group_t flex_group;
 
         if (atomic_read(&inode->i_count) > 1) {
                 printk(KERN_ERR "ext4_free_inode: inode has count=%d\n",
@@ -277,10 +276,10 @@ void ext4_free_inode(handle_t *handle, struct inode *inode)
                                 percpu_counter_dec(&sbi->s_dirs_counter);
 
                         if (sbi->s_log_groups_per_flex) {
-                                flex_group = ext4_flex_group(sbi, block_group);
-                                spin_lock(sb_bgl_lock(sbi, flex_group));
-                                sbi->s_flex_groups[flex_group].free_inodes++;
-                                spin_unlock(sb_bgl_lock(sbi, flex_group));
+                                ext4_group_t f;
+
+                                f = ext4_flex_group(sbi, block_group);
+                                atomic_inc(&sbi->s_flex_groups[f].free_inodes);
                         }
                 }
                 BUFFER_TRACE(bh2, "call ext4_handle_dirty_metadata");
@@ -360,9 +359,9 @@ static int find_group_flex(struct super_block *sb, struct inode *parent,
                 sbi->s_log_groups_per_flex;
 
 find_close_to_parent:
-        flexbg_free_blocks = flex_group[best_flex].free_blocks;
+        flexbg_free_blocks = atomic_read(&flex_group[best_flex].free_blocks);
         flex_freeb_ratio = flexbg_free_blocks * 100 / blocks_per_flex;
-        if (flex_group[best_flex].free_inodes &&
+        if (atomic_read(&flex_group[best_flex].free_inodes) &&
             flex_freeb_ratio > free_block_ratio)
                 goto found_flexbg;
 
@@ -375,24 +374,24 @@ find_close_to_parent:
                 if (i == parent_fbg_group || i == parent_fbg_group - 1)
                         continue;
 
-                flexbg_free_blocks = flex_group[i].free_blocks;
+                flexbg_free_blocks = atomic_read(&flex_group[i].free_blocks);
                 flex_freeb_ratio = flexbg_free_blocks * 100 / blocks_per_flex;
 
                 if (flex_freeb_ratio > free_block_ratio &&
-                    flex_group[i].free_inodes) {
+                    (atomic_read(&flex_group[i].free_inodes))) {
                         best_flex = i;
                         goto found_flexbg;
                 }
 
-                if (flex_group[best_flex].free_inodes == 0 ||
-                    (flex_group[i].free_blocks >
-                     flex_group[best_flex].free_blocks &&
-                     flex_group[i].free_inodes))
+                if ((atomic_read(&flex_group[best_flex].free_inodes) == 0) ||
+                    ((atomic_read(&flex_group[i].free_blocks) >
+                      atomic_read(&flex_group[best_flex].free_blocks)) &&
+                     atomic_read(&flex_group[i].free_inodes)))
                         best_flex = i;
         }
 
-        if (!flex_group[best_flex].free_inodes ||
-            !flex_group[best_flex].free_blocks)
+        if (!atomic_read(&flex_group[best_flex].free_inodes) ||
+            !atomic_read(&flex_group[best_flex].free_blocks))
                 return -1;
 
 found_flexbg:
@@ -960,9 +959,7 @@ got:
 
         if (sbi->s_log_groups_per_flex) {
                 flex_group = ext4_flex_group(sbi, group);
-                spin_lock(sb_bgl_lock(sbi, flex_group));
-                sbi->s_flex_groups[flex_group].free_inodes--;
-                spin_unlock(sb_bgl_lock(sbi, flex_group));
+                atomic_dec(&sbi->s_flex_groups[flex_group].free_inodes);
         }
 
         inode->i_uid = current_fsuid();