[PATCH] btrfs: add mount option to set commit interval

[David Sterba <dsterba@suse.cz>]

I'ts hardcoded to 30 seconds which is fine for most users. Higher values
defer data being synced to permanent storage with obvious consequences
when the system crashes. The upper bound is not forced, but a warning is
printed if it's more than 300 seconds (5 minutes).

Signed-off-by: David Sterba <dsterba@suse.cz>
---
 fs/btrfs/ctree.h   |  3 +++
 fs/btrfs/disk-io.c |  6 ++++--
 fs/btrfs/super.c   | 23 +++++++++++++++++++++++
 3 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index d6dd49b..6f7b607 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1338,6 +1338,7 @@ struct btrfs_fs_info {
 	u64 last_trans_log_full_commit;
 	unsigned long mount_opt;
 	unsigned long compress_type:4;
+	int commit_interval;
 	/*
 	 * It is a suggestive number, the read side is safe even it gets a
 	 * wrong number because we will write out the data into a regular
@@ -1928,6 +1929,8 @@ struct btrfs_ioctl_defrag_range_args {
 #define BTRFS_MOUNT_CHECK_INTEGRITY_INCLUDING_EXTENT_DATA (1 << 21)
 #define BTRFS_MOUNT_PANIC_ON_FATAL_ERROR	(1 << 22)
 
+#define BTRFS_DEFAULT_COMMIT_INTERVAL	(30)
+
 #define btrfs_clear_opt(o, opt)		((o) &= ~BTRFS_MOUNT_##opt)
 #define btrfs_set_opt(o, opt)		((o) |= BTRFS_MOUNT_##opt)
 #define btrfs_raw_test_opt(o, opt)	((o) & BTRFS_MOUNT_##opt)
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index b0292b3..d366043 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1714,7 +1714,7 @@ static int transaction_kthread(void *arg)
 
 	do {
 		cannot_commit = false;
-		delay = HZ * 30;
+		delay = HZ * root->fs_info->commit_interval;
 		mutex_lock(&root->fs_info->transaction_kthread_mutex);
 
 		spin_lock(&root->fs_info->trans_lock);
@@ -1726,7 +1726,8 @@ static int transaction_kthread(void *arg)
 
 		now = get_seconds();
 		if (!cur->blocked &&
-		    (now < cur->start_time || now - cur->start_time < 30)) {
+		    (now < cur->start_time ||
+		     now - cur->start_time < root->fs_info->commit_interval)) {
 			spin_unlock(&root->fs_info->trans_lock);
 			delay = HZ * 5;
 			goto sleep;
@@ -2173,6 +2174,7 @@ int open_ctree(struct super_block *sb,
 	fs_info->trans_no_join = 0;
 	fs_info->free_chunk_space = 0;
 	fs_info->tree_mod_log = RB_ROOT;
+	fs_info->commit_interval = BTRFS_DEFAULT_COMMIT_INTERVAL;
 
 	/* readahead state */
 	INIT_RADIX_TREE(&fs_info->reada_tree, GFP_NOFS & ~__GFP_WAIT);
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index f0857e0..4cc950f 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -319,6 +319,7 @@ enum {
 	Opt_no_space_cache, Opt_recovery, Opt_skip_balance,
 	Opt_check_integrity, Opt_check_integrity_including_extent_data,
 	Opt_check_integrity_print_mask, Opt_fatal_errors,
+	Opt_commit_interval,
 	Opt_err,
 };
 
@@ -359,6 +360,7 @@ static match_table_t tokens = {
 	{Opt_check_integrity_including_extent_data, "check_int_data"},
 	{Opt_check_integrity_print_mask, "check_int_print_mask=%d"},
 	{Opt_fatal_errors, "fatal_errors=%s"},
+	{Opt_commit_interval, "commit=%d"},
 	{Opt_err, NULL},
 };
 
@@ -624,6 +626,27 @@ int btrfs_parse_options(struct btrfs_root *root, char *options)
 				goto out;
 			}
 			break;
+		case Opt_commit_interval:
+			intarg = 0;
+			ret = match_int(&args[0], &intarg);
+			if (ret < 0) {
+				printk(KERN_ERR
+					"btrfs: invalid commit interval\n", ret);
+				ret = -EINVAL;
+			}
+			if (intarg > 0) {
+				if (intarg > 300) {
+					printk(KERN_WARNING
+					    "btrfs: excessive commit interval %d\n",
+							intarg);
+				}
+				info->commit_interval = intarg;
+			} else {
+				printk(KERN_INFO
+				    "btrfs: using default commit interval %ds\n",
+				    BTRFS_DEFAULT_COMMIT_INTERVAL);
+				info->commit_interval = BTRFS_DEFAULT_COMMIT_INTERVAL;
+			}
 		case Opt_err:
 			printk(KERN_INFO "btrfs: unrecognized mount option "
 			       "'%s'\n", p);
-- 
1.8.1.4