[PATCH 5.10 064/122] btrfs: do not pin logs too early during renames

Greg Kroah-Hartman
2024-02-27T14:28:25Z

From: Filipe Manana <fdmanana@suse.com>

[ Upstream commit bd54f381a12ac695593271a663d36d14220215b2 ]

During renames we pin the logs of the roots a bit too early, before the
calls to btrfs_insert_inode_ref(). We can pin the logs after those calls,
since those will not change anything in a log tree.

In a scenario where we have multiple and diverse filesystem operations
running in parallel, those calls can take a significant amount of time,
due to lock contention on extent buffers, and delay log commits from other
tasks for longer than necessary.

So just pin logs after calls to btrfs_insert_inode_ref() and right before
the first operation that can update a log tree.

The following script that uses dbench was used for testing:

$ cat dbench-test.sh
#!/bin/bash

DEV=/dev/nvme0n1
MNT=/mnt/nvme0n1
MOUNT_OPTIONS="-o ssd"
MKFS_OPTIONS="-m single -d single"

echo "performance" | tee /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor

umount $DEV &> /dev/null
mkfs.btrfs -f $MKFS_OPTIONS $DEV
mount $MOUNT_OPTIONS $DEV $MNT

dbench -D $MNT -t 120 16

umount $MNT

The tests were run on a machine with 12 cores, 64G of RAN, a NVMe device
and using a non-debug kernel config (Debian's default config).

The results compare a branch without this patch and without the previous
patch in the series, that has the subject:

"btrfs: eliminate some false positives when checking if inode was logged"

Versus the same branch with these two patches applied.

dbench with 8 clients, results before:

Operation Count AvgLat MaxLat
----------------------------------------
NTCreateX 4391359 0.009 249.745
Close 3225882 0.001 3.243
Rename 185953 0.065 240.643
Unlink 886669 0.049 249.906
Deltree 112 2.455 217.433
Mkdir 56 0.002 0.004
Qpathinfo 3980281 0.004 3.109
Qfileinfo 697579 0.001 0.187
Qfsinfo 729780 0.002 2.424
Sfileinfo 357764 0.004 1.415
Find 1538861 0.016 4.863
WriteX 2189666 0.010 3.327
ReadX 6883443 0.002 0.729
LockX 14298 0.002 0.073
UnlockX 14298 0.001 0.042
Flush 307777 2.447 303.663

Throughput 1149.6 MB/sec 8 clients 8 procs max_latency=303.666 ms

dbench with 8 clients, results after:

Operation Count AvgLat MaxLat
----------------------------------------
NTCreateX 4269920 0.009 213.532
Close 3136653 0.001 0.690
Rename 180805 0.082 213.858
Unlink 862189 0.050 172.893
Deltree 112 2.998 218.328
Mkdir 56 0.002 0.003
Qpathinfo 3870158 0.004 5.072
Qfileinfo 678375 0.001 0.194
Qfsinfo 709604 0.002 0.485
Sfileinfo 347850 0.004 1.304
Find 1496310 0.017 5.504
WriteX 2129613 0.010 2.882
ReadX 6693066 0.002 1.517
LockX 13902 0.002 0.075
UnlockX 13902 0.001 0.055
Flush 299276 2.511 220.189

Throughput 1187.33 MB/sec 8 clients 8 procs max_latency=220.194 ms

+3.2% throughput, -31.8% max latency

dbench with 16 clients, results before:

Operation Count AvgLat MaxLat
----------------------------------------
NTCreateX 5978334 0.028 156.507
Close 4391598 0.001 1.345
Rename 253136 0.241 155.057
Unlink 1207220 0.182 257.344
Deltree 160 6.123 36.277
Mkdir 80 0.003 0.005
Qpathinfo 5418817 0.012 6.867
Qfileinfo 949929 0.001 0.941
Qfsinfo 993560 0.002 1.386
Sfileinfo 486904 0.004 2.829
Find 2095088 0.059 8.164
WriteX 2982319 0.017 9.029
ReadX 9371484 0.002 4.052
LockX 19470 0.002 0.461
UnlockX 19470 0.001 0.990
Flush 418936 2.740 347.902

Throughput 1495.31 MB/sec 16 clients 16 procs max_latency=347.909 ms

dbench with 16 clients, results after:

Operation Count AvgLat MaxLat
----------------------------------------
NTCreateX 5711833 0.029 131.240
Close 4195897 0.001 1.732
Rename 241849 0.204 147.831
Unlink 1153341 0.184 231.322
Deltree 160 6.086 30.198
Mkdir 80 0.003 0.021
Qpathinfo 5177011 0.012 7.150
Qfileinfo 907768 0.001 0.793
Qfsinfo 949205 0.002 1.431
Sfileinfo 465317 0.004 2.454
Find 2001541 0.058 7.819
WriteX 2850661 0.017 9.110
ReadX 8952289 0.002 3.991
LockX 18596 0.002 0.655
UnlockX 18596 0.001 0.179
Flush 400342 2.879 293.607

Throughput 1565.73 MB/sec 16 clients 16 procs max_latency=293.611 ms

+4.6% throughput, -16.9% max latency

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/btrfs/inode.c | 48 ++++++++++++++++++++++++++++++++++++++++++------
1 file changed, 42 insertions(+), 6 deletions(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 250b6064876de..591caac2bf814 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -8968,8 +8968,6 @@ static int btrfs_rename_exchange(struct inode *old_dir,
/* force full log commit if subvolume involved. */
btrfs_set_log_full_commit(trans);
} else {
- btrfs_pin_log_trans(root);
- root_log_pinned = true;
ret = btrfs_insert_inode_ref(trans, dest,
new_dentry->d_name.name,
new_dentry->d_name.len,
@@ -8986,8 +8984,6 @@ static int btrfs_rename_exchange(struct inode *old_dir,
/* force full log commit if subvolume involved. */
btrfs_set_log_full_commit(trans);
} else {
- btrfs_pin_log_trans(dest);
- dest_log_pinned = true;
ret = btrfs_insert_inode_ref(trans, root,
old_dentry->d_name.name,
old_dentry->d_name.len,
@@ -9018,6 +9014,29 @@ static int btrfs_rename_exchange(struct inode *old_dir,
BTRFS_I(new_inode), 1);
}

+ /*
+ * Now pin the logs of the roots. We do it to ensure that no other task
+ * can sync the logs while we are in progress with the rename, because
+ * that could result in an inconsistency in case any of the inodes that
+ * are part of this rename operation were logged before.
+ *
+ * We pin the logs even if at this precise moment none of the inodes was
+ * logged before. This is because right after we checked for that, some
+ * other task fsyncing some other inode not involved with this rename
+ * operation could log that one of our inodes exists.
+ *
+ * We don't need to pin the logs before the above calls to
+ * btrfs_insert_inode_ref(), since those don't ever need to change a log.
+ */
+ if (old_ino != BTRFS_FIRST_FREE_OBJECTID) {
+ btrfs_pin_log_trans(root);
+ root_log_pinned = true;
+ }
+ if (new_ino != BTRFS_FIRST_FREE_OBJECTID) {
+ btrfs_pin_log_trans(dest);
+ dest_log_pinned = true;
+ }
+
/* src is a subvolume */
if (old_ino == BTRFS_FIRST_FREE_OBJECTID) {
ret = btrfs_unlink_subvol(trans, old_dir, old_dentry);
@@ -9267,8 +9286,6 @@ static int btrfs_rename(struct inode *old_dir, struct dentry *old_dentry,
/* force full log commit if subvolume involved. */
btrfs_set_log_full_commit(trans);
} else {
- btrfs_pin_log_trans(root);
- log_pinned = true;
ret = btrfs_insert_inode_ref(trans, dest,
new_dentry->d_name.name,
new_dentry->d_name.len,
@@ -9292,6 +9309,25 @@ static int btrfs_rename(struct inode *old_dir, struct dentry *old_dentry,
if (unlikely(old_ino == BTRFS_FIRST_FREE_OBJECTID)) {
ret = btrfs_unlink_subvol(trans, old_dir, old_dentry);
} else {
+ /*
+ * Now pin the log. We do it to ensure that no other task can
+ * sync the log while we are in progress with the rename, as
+ * that could result in an inconsistency in case any of the
+ * inodes that are part of this rename operation were logged
+ * before.
+ *
+ * We pin the log even if at this precise moment none of the
+ * inodes was logged before. This is because right after we
+ * checked for that, some other task fsyncing some other inode
+ * not involved with this rename operation could log that one of
+ * our inodes exists.
+ *
+ * We don't need to pin the logs before the above call to
+ * btrfs_insert_inode_ref(), since that does not need to change
+ * a log.
+ */
+ btrfs_pin_log_trans(root);
+ log_pinned = true;
ret = __btrfs_unlink_inode(trans, root, BTRFS_I(old_dir),
BTRFS_I(d_inode(old_dentry)),
old_dentry->d_name.name,
--
2.43.0