ext4: Make the length of the mb_history file tunable

In memory-constrained systems with many partitions, the ~68K for each
partition for the mb_history buffer can be excessive.

This patch adds a new mount option, mb_history_length, as well as a
way of setting the default via a module parameter (or via a sysfs
parameter in /sys/module/ext4/parameter/default_mb_history_length).
If the mb_history_length is set to zero, the mb_history facility is
disabled entirely.

Signed-off-by: Curt Wohlgemuth <curtw@google.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 7 insertions, 6 deletions

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index dbd47eac13e..df75855ae6f 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2413,7 +2413,8 @@ static void ext4_mb_history_release(struct super_block *sb)
 
         if (sbi->s_proc != NULL) {
                 remove_proc_entry("mb_groups", sbi->s_proc);
-                remove_proc_entry("mb_history", sbi->s_proc);
+                if (sbi->s_mb_history_max)
+                        remove_proc_entry("mb_history", sbi->s_proc);
         }
         kfree(sbi->s_mb_history);
 }
@@ -2424,17 +2425,17 @@ static void ext4_mb_history_init(struct super_block *sb)
         int i;
 
         if (sbi->s_proc != NULL) {
-                proc_create_data("mb_history", S_IRUGO, sbi->s_proc,
-                                 &ext4_mb_seq_history_fops, sb);
+                if (sbi->s_mb_history_max)
+                        proc_create_data("mb_history", S_IRUGO, sbi->s_proc,
+                                         &ext4_mb_seq_history_fops, sb);
                 proc_create_data("mb_groups", S_IRUGO, sbi->s_proc,
                                  &ext4_mb_seq_groups_fops, sb);
         }
 
-        sbi->s_mb_history_max = 1000;
         sbi->s_mb_history_cur = 0;
         spin_lock_init(&sbi->s_mb_history_lock);
         i = sbi->s_mb_history_max * sizeof(struct ext4_mb_history);
-        sbi->s_mb_history = kzalloc(i, GFP_KERNEL);
+        sbi->s_mb_history = i ? kzalloc(i, GFP_KERNEL) : NULL;
         /* if we can't allocate history, then we simple won't use it */
 }
 
@@ -2444,7 +2445,7 @@ ext4_mb_store_history(struct ext4_allocation_context *ac)
         struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
         struct ext4_mb_history h;
 
-        if (unlikely(sbi->s_mb_history == NULL))
+        if (sbi->s_mb_history == NULL)
                 return;
 
         if (!(ac->ac_op & sbi->s_mb_history_filter))