summaryrefslogtreecommitdiffstats
path: root/fs/btrfs/tree-log.c
diff options
context:
space:
mode:
authorFilipe Manana <fdmanana@suse.com>2020-11-25 12:19:28 +0000
committerDavid Sterba <dsterba@suse.com>2020-12-09 19:16:07 +0100
commit47876f7ceffa0e6af7476e052b3c061f1f2c1d9f (patch)
treec58d818b71c95c037acdc5dbdd3191f3cdd52453 /fs/btrfs/tree-log.c
parent639bd575b7c7fa326abadd2ef3e374a5a24eb40b (diff)
downloadlinux-47876f7ceffa0e6af7476e052b3c061f1f2c1d9f.tar.bz2
btrfs: do not block inode logging for so long during transaction commit
Early on during a transaction commit we acquire the tree_log_mutex and hold it until after we write the super blocks. But before writing the extent buffers dirtied by the transaction and the super blocks we unblock the transaction by setting its state to TRANS_STATE_UNBLOCKED and setting fs_info->running_transaction to NULL. This means that after that and before writing the super blocks, new transactions can start. However if any transaction wants to log an inode, it will block waiting for the transaction commit to write its dirty extent buffers and the super blocks because the tree_log_mutex is only released after those operations are complete, and starting a new log transaction blocks on that mutex (at start_log_trans()). Writing the dirty extent buffers and the super blocks can take a very significant amount of time to complete, but we could allow the tasks wanting to log an inode to proceed with most of their steps: 1) create the log trees 2) log metadata in the trees 3) write their dirty extent buffers They only need to wait for the previous transaction commit to complete (write its super blocks) before they attempt to write their super blocks, otherwise we could end up with a corrupt filesystem after a crash. So change start_log_trans() to use the root tree's log_mutex to serialize for the creation of the log root tree instead of using the tree_log_mutex, and make btrfs_sync_log() acquire the tree_log_mutex before writing the super blocks. This allows for inode logging to wait much less time when there is a previous transaction that is still committing, often not having to wait at all, as by the time when we try to sync the log the previous transaction already wrote its super blocks. This patch belongs to a patch set that is comprised of the following patches: btrfs: fix race causing unnecessary inode logging during link and rename btrfs: fix race that results in logging old extents during a fast fsync btrfs: fix race that causes unnecessary logging of ancestor inodes btrfs: fix race that makes inode logging fallback to transaction commit btrfs: fix race leading to unnecessary transaction commit when logging inode btrfs: do not block inode logging for so long during transaction commit The following script that uses dbench was used to measure the impact of the whole patchset: $ cat test-dbench.sh #!/bin/bash DEV=/dev/nvme0n1 MNT=/mnt/btrfs MOUNT_OPTIONS="-o ssd" echo "performance" | \ tee /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor mkfs.btrfs -f -m single -d single $DEV mount $MOUNT_OPTIONS $DEV $MNT dbench -D $MNT -t 300 64 umount $MNT The test was run on a machine with 12 cores, 64G of ram, using a NVMe device and a non-debug kernel configuration (Debian's default). Before patch set: Operation Count AvgLat MaxLat ---------------------------------------- NTCreateX 11277211 0.250 85.340 Close 8283172 0.002 6.479 Rename 477515 1.935 86.026 Unlink 2277936 0.770 87.071 Deltree 256 15.732 81.379 Mkdir 128 0.003 0.009 Qpathinfo 10221180 0.056 44.404 Qfileinfo 1789967 0.002 4.066 Qfsinfo 1874399 0.003 9.176 Sfileinfo 918589 0.061 10.247 Find 3951758 0.341 54.040 WriteX 5616547 0.047 85.079 ReadX 17676028 0.005 9.704 LockX 36704 0.003 1.800 UnlockX 36704 0.002 0.687 Flush 790541 14.115 676.236 Throughput 1179.19 MB/sec 64 clients 64 procs max_latency=676.240 ms After patch set: Operation Count AvgLat MaxLat ---------------------------------------- NTCreateX 12687926 0.171 86.526 Close 9320780 0.002 8.063 Rename 537253 1.444 78.576 Unlink 2561827 0.559 87.228 Deltree 374 11.499 73.549 Mkdir 187 0.003 0.005 Qpathinfo 11500300 0.061 36.801 Qfileinfo 2017118 0.002 7.189 Qfsinfo 2108641 0.003 4.825 Sfileinfo 1033574 0.008 8.065 Find 4446553 0.408 47.835 WriteX 6335667 0.045 84.388 ReadX 19887312 0.003 9.215 LockX 41312 0.003 1.394 UnlockX 41312 0.002 1.425 Flush 889233 13.014 623.259 Throughput 1339.32 MB/sec 64 clients 64 procs max_latency=623.265 ms +12.7% throughput, -8.2% max latency Signed-off-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
Diffstat (limited to 'fs/btrfs/tree-log.c')
-rw-r--r--fs/btrfs/tree-log.c56
1 files changed, 39 insertions, 17 deletions
diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index 582911a36ee0..254c2ee43aae 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -138,8 +138,25 @@ static int start_log_trans(struct btrfs_trans_handle *trans,
struct btrfs_log_ctx *ctx)
{
struct btrfs_fs_info *fs_info = root->fs_info;
+ struct btrfs_root *tree_root = fs_info->tree_root;
int ret = 0;
+ /*
+ * First check if the log root tree was already created. If not, create
+ * it before locking the root's log_mutex, just to keep lockdep happy.
+ */
+ if (!test_bit(BTRFS_ROOT_HAS_LOG_TREE, &tree_root->state)) {
+ mutex_lock(&tree_root->log_mutex);
+ if (!fs_info->log_root_tree) {
+ ret = btrfs_init_log_root_tree(trans, fs_info);
+ if (!ret)
+ set_bit(BTRFS_ROOT_HAS_LOG_TREE, &tree_root->state);
+ }
+ mutex_unlock(&tree_root->log_mutex);
+ if (ret)
+ return ret;
+ }
+
mutex_lock(&root->log_mutex);
if (root->log_root) {
@@ -155,13 +172,6 @@ static int start_log_trans(struct btrfs_trans_handle *trans,
set_bit(BTRFS_ROOT_MULTI_LOG_TASKS, &root->state);
}
} else {
- mutex_lock(&fs_info->tree_log_mutex);
- if (!fs_info->log_root_tree)
- ret = btrfs_init_log_root_tree(trans, fs_info);
- mutex_unlock(&fs_info->tree_log_mutex);
- if (ret)
- goto out;
-
ret = btrfs_add_log_tree(trans, root);
if (ret)
goto out;
@@ -3021,6 +3031,8 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans,
int log_transid = 0;
struct btrfs_log_ctx root_log_ctx;
struct blk_plug plug;
+ u64 log_root_start;
+ u64 log_root_level;
mutex_lock(&root->log_mutex);
log_transid = ctx->log_transid;
@@ -3198,22 +3210,31 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans,
goto out_wake_log_root;
}
- btrfs_set_super_log_root(fs_info->super_for_commit,
- log_root_tree->node->start);
- btrfs_set_super_log_root_level(fs_info->super_for_commit,
- btrfs_header_level(log_root_tree->node));
-
+ log_root_start = log_root_tree->node->start;
+ log_root_level = btrfs_header_level(log_root_tree->node);
log_root_tree->log_transid++;
mutex_unlock(&log_root_tree->log_mutex);
/*
- * Nobody else is going to jump in and write the ctree
- * super here because the log_commit atomic below is protecting
- * us. We must be called with a transaction handle pinning
- * the running transaction open, so a full commit can't hop
- * in and cause problems either.
+ * Here we are guaranteed that nobody is going to write the superblock
+ * for the current transaction before us and that neither we do write
+ * our superblock before the previous transaction finishes its commit
+ * and writes its superblock, because:
+ *
+ * 1) We are holding a handle on the current transaction, so no body
+ * can commit it until we release the handle;
+ *
+ * 2) Before writing our superblock we acquire the tree_log_mutex, so
+ * if the previous transaction is still committing, and hasn't yet
+ * written its superblock, we wait for it to do it, because a
+ * transaction commit acquires the tree_log_mutex when the commit
+ * begins and releases it only after writing its superblock.
*/
+ mutex_lock(&fs_info->tree_log_mutex);
+ btrfs_set_super_log_root(fs_info->super_for_commit, log_root_start);
+ btrfs_set_super_log_root_level(fs_info->super_for_commit, log_root_level);
ret = write_all_supers(fs_info, 1);
+ mutex_unlock(&fs_info->tree_log_mutex);
if (ret) {
btrfs_set_log_full_commit(trans);
btrfs_abort_transaction(trans, ret);
@@ -3298,6 +3319,7 @@ int btrfs_free_log_root_tree(struct btrfs_trans_handle *trans,
if (fs_info->log_root_tree) {
free_log_tree(trans, fs_info->log_root_tree);
fs_info->log_root_tree = NULL;
+ clear_bit(BTRFS_ROOT_HAS_LOG_TREE, &fs_info->tree_root->state);
}
return 0;
}