ext4: add fsync batch tuning knobs

Add new mount options, min_batch_time and max_batch_time, which
controls how long the jbd2 layer should wait for additional filesystem
operations to get batched with a synchronous write transaction.

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

7 files changed, 91 insertions, 8 deletions

diff --git a/Documentation/filesystems/ext4.txt b/Documentation/filesystems/ext4.txt
index f75ab101c00a..e3fcbea3ec8c 100644
--- a/Documentation/filesystems/ext4.txt
+++ b/Documentation/filesystems/ext4.txt
@@ -283,6 +283,35 @@ delalloc	(*)	Deferring block allocation until write-out time.
 nodelalloc              Disable delayed allocation. Blocks are allocation
                         when data is copied from user to page cache.
 
+max_batch_time=usec     Maximum amount of time ext4 should wait for
+                        additional filesystem operations to be batch
+                        together with a synchronous write operation.
+                        Since a synchronous write operation is going to
+                        force a commit and then a wait for the I/O
+                        complete, it doesn't cost much, and can be a
+                        huge throughput win, we wait for a small amount
+                        of time to see if any other transactions can
+                        piggyback on the synchronous write.   The
+                        algorithm used is designed to automatically tune
+                        for the speed of the disk, by measuring the
+                        amount of time (on average) that it takes to
+                        finish committing a transaction.  Call this time
+                        the "commit time".  If the time that the
+                        transactoin has been running is less than the
+                        commit time, ext4 will try sleeping for the
+                        commit time to see if other operations will join
+                        the transaction.   The commit time is capped by
+                        the max_batch_time, which defaults to 15000us
+                        (15ms).   This optimization can be turned off
+                        entirely by setting max_batch_time to 0.
+
+min_batch_time=usec     This parameter sets the commit time (as
+                        described above) to be at least min_batch_time.
+                        It defaults to zero microseconds.  Increasing
+                        this parameter may improve the throughput of
+                        multi-threaded, synchronous workloads on very
+                        fast disks, at the cost of increasing latency.
+
 Data Mode
 =========
 There are 3 different data modes:
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index ac8551e0b70a..9ba9fd6d14da 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -328,6 +328,7 @@ struct ext4_mount_options {
         uid_t s_resuid;
         gid_t s_resgid;
         unsigned long s_commit_interval;
+        u32 s_min_batch_time, s_max_batch_time;
 #ifdef CONFIG_QUOTA
         int s_jquota_fmt;
         char *s_qf_names[MAXQUOTAS];
@@ -806,6 +807,12 @@ static inline int ext4_valid_inum(struct super_block *sb, unsigned long ino)
 #define EXT4_DEFM_JMODE_WBACK   0x0060
 
 /*
+ * Default journal batch times
+ */
+#define EXT4_DEF_MIN_BATCH_TIME 0
+#define EXT4_DEF_MAX_BATCH_TIME 15000 /* 15ms */
+
+/*
  * Structure of a directory entry
  */
 #define EXT4_NAME_LEN 255
diff --git a/fs/ext4/ext4_sb.h b/fs/ext4/ext4_sb.h
index 3db800f399a6..039b6ea1a042 100644
--- a/fs/ext4/ext4_sb.h
+++ b/fs/ext4/ext4_sb.h
@@ -74,6 +74,8 @@ struct ext4_sb_info {
         struct journal_s *s_journal;
         struct list_head s_orphan;
         unsigned long s_commit_interval;
+        u32 s_max_batch_time;
+        u32 s_min_batch_time;
         struct block_device *journal_bdev;
 #ifdef CONFIG_JBD2_DEBUG
         struct timer_list turn_ro_timer;        /* For turning read-only (crash simulation) */
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index dc27d4c613c0..da377f9521bb 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -705,10 +705,19 @@ static int ext4_show_options(struct seq_file *seq, struct vfsmount *vfs)
 #endif
         if (!test_opt(sb, RESERVATION))
                 seq_puts(seq, ",noreservation");
-        if (sbi->s_commit_interval) {
+        if (sbi->s_commit_interval != JBD2_DEFAULT_MAX_COMMIT_AGE*HZ) {
                 seq_printf(seq, ",commit=%u",
                            (unsigned) (sbi->s_commit_interval / HZ));
         }
+        if (sbi->s_min_batch_time != EXT4_DEF_MIN_BATCH_TIME) {
+                seq_printf(seq, ",min_batch_time=%u",
+                           (unsigned) sbi->s_min_batch_time);
+        }
+        if (sbi->s_max_batch_time != EXT4_DEF_MAX_BATCH_TIME) {
+                seq_printf(seq, ",max_batch_time=%u",
+                           (unsigned) sbi->s_min_batch_time);
+        }
+
         /*
          * We're changing the default of barrier mount option, so
          * let's always display its mount state so it's clear what its
@@ -874,7 +883,8 @@ enum {
         Opt_nouid32, Opt_debug, Opt_oldalloc, Opt_orlov,
         Opt_user_xattr, Opt_nouser_xattr, Opt_acl, Opt_noacl,
         Opt_reservation, Opt_noreservation, Opt_noload, Opt_nobh, Opt_bh,
-        Opt_commit, Opt_journal_update, Opt_journal_inum, Opt_journal_dev,
+        Opt_commit, Opt_min_batch_time, Opt_max_batch_time,
+        Opt_journal_update, Opt_journal_inum, 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,
@@ -913,6 +923,8 @@ static const match_table_t tokens = {
         {Opt_nobh, "nobh"},
         {Opt_bh, "bh"},
         {Opt_commit, "commit=%u"},
+        {Opt_min_batch_time, "min_batch_time=%u"},
+        {Opt_max_batch_time, "max_batch_time=%u"},
         {Opt_journal_update, "journal=update"},
         {Opt_journal_inum, "journal=%u"},
         {Opt_journal_dev, "journal_dev=%u"},
@@ -1131,6 +1143,22 @@ static int parse_options(char *options, struct super_block *sb,
                                 option = JBD2_DEFAULT_MAX_COMMIT_AGE;
                         sbi->s_commit_interval = HZ * option;
                         break;
+                case Opt_max_batch_time:
+                        if (match_int(&args[0], &option))
+                                return 0;
+                        if (option < 0)
+                                return 0;
+                        if (option == 0)
+                                option = EXT4_DEF_MAX_BATCH_TIME;
+                        sbi->s_max_batch_time = option;
+                        break;
+                case Opt_min_batch_time:
+                        if (match_int(&args[0], &option))
+                                return 0;
+                        if (option < 0)
+                                return 0;
+                        sbi->s_min_batch_time = option;
+                        break;
                 case Opt_data_journal:
                         data_opt = EXT4_MOUNT_JOURNAL_DATA;
                         goto datacheck;
@@ -1979,6 +2007,9 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 
         sbi->s_resuid = le16_to_cpu(es->s_def_resuid);
         sbi->s_resgid = le16_to_cpu(es->s_def_resgid);
+        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;
 
         set_opt(sbi->s_mount_opt, RESERVATION);
         set_opt(sbi->s_mount_opt, BARRIER);
@@ -2524,11 +2555,9 @@ static void ext4_init_journal_params(struct super_block *sb, journal_t *journal)
 {
         struct ext4_sb_info *sbi = EXT4_SB(sb);
 
-        if (sbi->s_commit_interval)
-                journal->j_commit_interval = sbi->s_commit_interval;
-        /* We could also set up an ext4-specific default for the commit
-         * interval here, but for now we'll just fall back to the jbd
-         * default. */
+        journal->j_commit_interval = sbi->s_commit_interval;
+        journal->j_min_batch_time = sbi->s_min_batch_time;
+        journal->j_max_batch_time = sbi->s_max_batch_time;
 
         spin_lock(&journal->j_state_lock);
         if (test_opt(sb, BARRIER))
@@ -3042,6 +3071,8 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data)
         old_opts.s_resuid = sbi->s_resuid;
         old_opts.s_resgid = sbi->s_resgid;
         old_opts.s_commit_interval = sbi->s_commit_interval;
+        old_opts.s_min_batch_time = sbi->s_min_batch_time;
+        old_opts.s_max_batch_time = sbi->s_max_batch_time;
 #ifdef CONFIG_QUOTA
         old_opts.s_jquota_fmt = sbi->s_jquota_fmt;
         for (i = 0; i < MAXQUOTAS; i++)
@@ -3178,6 +3209,8 @@ restore_opts:
         sbi->s_resuid = old_opts.s_resuid;
         sbi->s_resgid = old_opts.s_resgid;
         sbi->s_commit_interval = old_opts.s_commit_interval;
+        sbi->s_min_batch_time = old_opts.s_min_batch_time;
+        sbi->s_max_batch_time = old_opts.s_max_batch_time;
 #ifdef CONFIG_QUOTA
         sbi->s_jquota_fmt = old_opts.s_jquota_fmt;
         for (i = 0; i < MAXQUOTAS; i++) {
diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index 74d87290381c..fd1d7557a098 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -964,6 +964,8 @@ static journal_t * journal_init_common (void)
         spin_lock_init(&journal->j_state_lock);
 
         journal->j_commit_interval = (HZ * JBD2_DEFAULT_MAX_COMMIT_AGE);
+        journal->j_min_batch_time = 0;
+        journal->j_max_batch_time = 15000; /* 15ms */
 
         /* The journal is marked for error until we succeed with recovery! */
         journal->j_flags = JBD2_ABORT;
diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index 13dcbc990f41..48c21bac5a56 100644
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -1255,8 +1255,10 @@ int jbd2_journal_stop(handle_t *handle)
                 trans_time = ktime_to_ns(ktime_sub(ktime_get(),
                                                    transaction->t_start_time));
 
+                commit_time = max_t(u64, commit_time,
+                                    1000*journal->j_min_batch_time);
                 commit_time = min_t(u64, commit_time,
-                                    1000*jiffies_to_usecs(1));
+                                    1000*journal->j_max_batch_time);
 
                 if (trans_time < commit_time) {
                         ktime_t expires = ktime_add_ns(ktime_get(),
diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
index ab8cef130c28..a3cd647ea1bc 100644
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -956,6 +956,14 @@ struct journal_s
          */
         u64                     j_average_commit_time;
 
+        /*
+         * minimum and maximum times that we should wait for
+         * additional filesystem operations to get batched into a
+         * synchronous handle in microseconds
+         */
+        u32                     j_min_batch_time;
+        u32                     j_max_batch_time;
+
         /* This function is called when a transaction is closed */
         void                    (*j_commit_callback)(journal_t *,
                                                      transaction_t *);