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, 17 insertions, 1 deletions

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 7903f20c8075..39223a52bc71 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -47,6 +47,13 @@
 #include "xattr.h"
 #include "acl.h"
 
+static int default_mb_history_length = 1000;
+
+module_param_named(default_mb_history_length, default_mb_history_length,
+                   int, 0644);
+MODULE_PARM_DESC(default_mb_history_length,
+                 "Default number of entries saved for mb_history");
+
 struct proc_dir_entry *ext4_proc_root;
 static struct kset *ext4_kset;
 
@@ -1042,7 +1049,7 @@ enum {
         Opt_journal_update, Opt_journal_dev,
         Opt_journal_checksum, Opt_journal_async_commit,
         Opt_abort, Opt_data_journal, Opt_data_ordered, Opt_data_writeback,
-        Opt_data_err_abort, Opt_data_err_ignore,
+        Opt_data_err_abort, Opt_data_err_ignore, Opt_mb_history_length,
         Opt_usrjquota, Opt_grpjquota, Opt_offusrjquota, Opt_offgrpjquota,
         Opt_jqfmt_vfsold, Opt_jqfmt_vfsv0, Opt_quota, Opt_noquota,
         Opt_ignore, Opt_barrier, Opt_nobarrier, Opt_err, Opt_resize,
@@ -1088,6 +1095,7 @@ static const match_table_t tokens = {
         {Opt_data_writeback, "data=writeback"},
         {Opt_data_err_abort, "data_err=abort"},
         {Opt_data_err_ignore, "data_err=ignore"},
+        {Opt_mb_history_length, "mb_history_length=%u"},
         {Opt_offusrjquota, "usrjquota="},
         {Opt_usrjquota, "usrjquota=%s"},
         {Opt_offgrpjquota, "grpjquota="},
@@ -1329,6 +1337,13 @@ static int parse_options(char *options, struct super_block *sb,
                 case Opt_data_err_ignore:
                         clear_opt(sbi->s_mount_opt, DATA_ERR_ABORT);
                         break;
+                case Opt_mb_history_length:
+                        if (match_int(&args[0], &option))
+                                return 0;
+                        if (option < 0)
+                                return 0;
+                        sbi->s_mb_history_max = option;
+                        break;
 #ifdef CONFIG_QUOTA
                 case Opt_usrjquota:
                         qtype = USRQUOTA;
@@ -2345,6 +2360,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
         sbi->s_commit_interval = JBD2_DEFAULT_MAX_COMMIT_AGE * HZ;
         sbi->s_min_batch_time = EXT4_DEF_MIN_BATCH_TIME;
         sbi->s_max_batch_time = EXT4_DEF_MAX_BATCH_TIME;
+        sbi->s_mb_history_max = default_mb_history_length;
 
         set_opt(sbi->s_mount_opt, BARRIER);