* [PATCH 1/2] btrfs: avoid iterating over all indexes when logging directory
2023-04-05 17:51 [PATCH 0/2] btrfs: some fsync updates when logging directories fdmanana
@ 2023-04-05 17:51 ` fdmanana
2023-04-06 15:24 ` David Sterba
2023-04-05 17:51 ` [PATCH 2/2] btrfs: use log root when iterating over index keys " fdmanana
2023-04-06 18:52 ` [PATCH 0/2] btrfs: some fsync updates when logging directories David Sterba
2 siblings, 1 reply; 5+ messages in thread
From: fdmanana @ 2023-04-05 17:51 UTC (permalink / raw)
To: linux-btrfs
From: Filipe Manana <fdmanana@suse.com>
When logging a directory, after copying all directory index items from the
subvolume tree to the log tree, we iterate over the subvolume tree to find
all dir index items that are located in leaves COWed (or created) in the
current transaction. If we keep logging a directory several times during
the same transaction, we end up iterating over the same dir index items
everytime we log the directory, wasting time and adding extra lock
contention on the subvolume tree.
So just keep track of the last logged dir index offset in order to start
the search for that index (+1) the next time the directory is logged, as
dir index values (key offsets) come from a monotonically increasing
counter.
The following test measures the difference before and after this change:
$ cat test.sh
#!/bin/bash
DEV=/dev/nullb0
MNT=/mnt/nullb0
umount $DEV &> /dev/null
mkfs.btrfs -f $DEV
mount -o ssd $DEV $MNT
# Time values in milliseconds.
declare -a fsync_times
# Total number of files added to the test directory.
num_files=1000000
# Fsync directory after every N files are added.
fsync_period=100
mkdir $MNT/testdir
fsync_total_time=0
for ((i = 1; i <= $num_files; i++)); do
echo -n > $MNT/testdir/file_$i
if [ $((i % fsync_period)) -eq 0 ]; then
start=$(date +%s%N)
xfs_io -c "fsync" $MNT/testdir
end=$(date +%s%N)
fsync_total_time=$((fsync_total_time + (end - start)))
fsync_times[i]=$(( (end - start) / 1000000 ))
echo -n -e "Progress $i / $num_files\r"
fi
done
echo -e "\nHistogram of directory fsync duration in ms:\n"
printf '%s\n' "${fsync_times[@]}" | \
perl -MStatistics::Histogram -e '@d = <>; print get_histogram(\@d);'
fsync_total_time=$((fsync_total_time / 1000000))
echo -e "\nTotal time spent in fsync: $fsync_total_time ms\n"
echo
umount $MNT
The test was run on a non-debug kernel (Debian's default kernel config)
against a 15G null block device.
Result before this change:
Histogram of directory fsync duration in ms:
Count: 10000
Range: 3.000 - 362.000; Mean: 34.556; Median: 31.000; Stddev: 25.751
Percentiles: 90th: 71.000; 95th: 77.000; 99th: 81.000
3.000 - 5.278: 1423 #################################
5.278 - 8.854: 1173 ###########################
8.854 - 14.467: 591 ##############
14.467 - 23.277: 1025 #######################
23.277 - 37.105: 1422 #################################
37.105 - 58.809: 2036 ###############################################
58.809 - 92.876: 2316 #####################################################
92.876 - 146.346: 6 |
146.346 - 230.271: 6 |
230.271 - 362.000: 2 |
Total time spent in fsync: 350527 ms
Result after this change:
Histogram of directory fsync duration in ms:
Count: 10000
Range: 3.000 - 1088.000; Mean: 8.704; Median: 8.000; Stddev: 12.576
Percentiles: 90th: 12.000; 95th: 14.000; 99th: 17.000
3.000 - 6.007: 3222 #################################
6.007 - 11.276: 5197 #####################################################
11.276 - 20.506: 1551 ################
20.506 - 36.674: 24 |
36.674 - 201.552: 1 |
201.552 - 353.841: 4 |
353.841 - 1088.000: 1 |
Total time spent in fsync: 92114 ms
Signed-off-by: Filipe Manana <fdmanana@suse.com>
---
fs/btrfs/btrfs_inode.h | 32 +++++++++++++++++++++++++++-----
fs/btrfs/tree-log.c | 31 +++++++++++++++++++++++++++++--
2 files changed, 56 insertions(+), 7 deletions(-)
diff --git a/fs/btrfs/btrfs_inode.h b/fs/btrfs/btrfs_inode.h
index 9dc21622806e..f1e087994f87 100644
--- a/fs/btrfs/btrfs_inode.h
+++ b/fs/btrfs/btrfs_inode.h
@@ -142,11 +142,22 @@ struct btrfs_inode {
/* a local copy of root's last_log_commit */
int last_log_commit;
- /*
- * Total number of bytes pending delalloc, used by stat to calculate the
- * real block usage of the file. This is used only for files.
- */
- u64 delalloc_bytes;
+ union {
+ /*
+ * Total number of bytes pending delalloc, used by stat to
+ * calculate the real block usage of the file. This is used
+ * only for files.
+ */
+ u64 delalloc_bytes;
+ /*
+ * The lowest possible index of the next dir index key which
+ * points to an inode that needs to be logged.
+ * This is used only for directories.
+ * Use the helpers btrfs_get_first_dir_index_to_log() and
+ * btrfs_set_first_dir_index_to_log() to access this field.
+ */
+ u64 first_dir_index_to_log;
+ };
union {
/*
@@ -247,6 +258,17 @@ struct btrfs_inode {
struct inode vfs_inode;
};
+static inline u64 btrfs_get_first_dir_index_to_log(const struct btrfs_inode *inode)
+{
+ return READ_ONCE(inode->first_dir_index_to_log);
+}
+
+static inline void btrfs_set_first_dir_index_to_log(struct btrfs_inode *inode,
+ u64 index)
+{
+ WRITE_ONCE(inode->first_dir_index_to_log, index);
+}
+
static inline struct btrfs_inode *BTRFS_I(const struct inode *inode)
{
return container_of(inode, struct btrfs_inode, vfs_inode);
diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index 9ab793b638a7..c2a467276071 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -3648,6 +3648,9 @@ static int flush_dir_items_batch(struct btrfs_trans_handle *trans,
ret = BTRFS_LOG_FORCE_COMMIT;
else
inode->last_dir_index_offset = last_index;
+
+ if (btrfs_get_first_dir_index_to_log(inode) == 0)
+ btrfs_set_first_dir_index_to_log(inode, batch.keys[0].offset);
out:
kfree(ins_data);
@@ -5406,6 +5409,7 @@ static int log_new_dir_dentries(struct btrfs_trans_handle *trans,
LIST_HEAD(dir_list);
struct btrfs_dir_list *dir_elem;
u64 ino = btrfs_ino(start_inode);
+ struct btrfs_inode *curr_inode = start_inode;
int ret = 0;
/*
@@ -5420,18 +5424,22 @@ static int log_new_dir_dentries(struct btrfs_trans_handle *trans,
if (!path)
return -ENOMEM;
+ ihold(&curr_inode->vfs_inode);
+
while (true) {
+ struct inode *vfs_inode;
struct extent_buffer *leaf;
struct btrfs_key min_key;
+ u64 next_index;
bool continue_curr_inode = true;
int nritems;
int i;
min_key.objectid = ino;
min_key.type = BTRFS_DIR_INDEX_KEY;
- min_key.offset = 0;
+ min_key.offset = btrfs_get_first_dir_index_to_log(curr_inode);
+ next_index = min_key.offset;
again:
- btrfs_release_path(path);
ret = btrfs_search_forward(root, &min_key, path, trans->transid);
if (ret < 0) {
break;
@@ -5456,6 +5464,8 @@ static int log_new_dir_dentries(struct btrfs_trans_handle *trans,
break;
}
+ next_index = min_key.offset + 1;
+
di = btrfs_item_ptr(leaf, i, struct btrfs_dir_item);
type = btrfs_dir_ftype(leaf, di);
if (btrfs_dir_transid(leaf, di) < trans->transid)
@@ -5496,12 +5506,16 @@ static int log_new_dir_dentries(struct btrfs_trans_handle *trans,
break;
}
+ btrfs_release_path(path);
+
if (continue_curr_inode && min_key.offset < (u64)-1) {
min_key.offset++;
goto again;
}
next:
+ btrfs_set_first_dir_index_to_log(curr_inode, next_index);
+
if (list_empty(&dir_list))
break;
@@ -5509,9 +5523,22 @@ static int log_new_dir_dentries(struct btrfs_trans_handle *trans,
ino = dir_elem->ino;
list_del(&dir_elem->list);
kfree(dir_elem);
+
+ btrfs_add_delayed_iput(curr_inode);
+ curr_inode = NULL;
+
+ vfs_inode = btrfs_iget(fs_info->sb, ino, root);
+ if (IS_ERR(vfs_inode)) {
+ ret = PTR_ERR(vfs_inode);
+ break;
+ }
+ curr_inode = BTRFS_I(vfs_inode);
}
out:
btrfs_free_path(path);
+ if (curr_inode)
+ btrfs_add_delayed_iput(curr_inode);
+
if (ret) {
struct btrfs_dir_list *next;
--
2.34.1
^ permalink raw reply related [flat|nested] 5+ messages in thread* [PATCH 2/2] btrfs: use log root when iterating over index keys when logging directory
2023-04-05 17:51 [PATCH 0/2] btrfs: some fsync updates when logging directories fdmanana
2023-04-05 17:51 ` [PATCH 1/2] btrfs: avoid iterating over all indexes when logging directory fdmanana
@ 2023-04-05 17:51 ` fdmanana
2023-04-06 18:52 ` [PATCH 0/2] btrfs: some fsync updates when logging directories David Sterba
2 siblings, 0 replies; 5+ messages in thread
From: fdmanana @ 2023-04-05 17:51 UTC (permalink / raw)
To: linux-btrfs
From: Filipe Manana <fdmanana@suse.com>
When logging dir dentries of a directory, we iterate over the subvolume
tree to find dir index keys on leaves modified in the current transaction.
This however is heavy on locking, since btrfs_search_forward() may often
keep locks on extent buffers for quite a while when walking the tree to
find a suitable leaf modified in the current transaction and with a key
not smaller than then the provided minimum key. That means it will block
other tasks trying to access the subvolume tree, which may be common fs
operations like creating, renaming, linking, unlinking, reflinking files,
etc.
A better solution is to iterate the log tree, since it's much smaller than
a subvolume tree and just use plain btrfs_search_slot() (or the wrapper
btrfs_for_each_slot()) and only contains dir index keys added in the
current transaction.
The following bonnie++ test on a non-debug kernel (with Debian's default
kernel config) on a 20G null block device, was used to measure the impact:
$ cat test.sh
#!/bin/bash
DEV=/dev/nullb0
MNT=/mnt/nullb0
NR_DIRECTORIES=20
NR_FILES=20480 # must be a multiple of 1024
DATASET_SIZE=$(( (8 * 1024 * 1024 * 1024) / 1048576 )) # 8 GiB as megabytes
DIRECTORY_SIZE=$(( DATASET_SIZE / NR_FILES ))
NR_FILES=$(( NR_FILES / 1024 ))
umount $DEV &> /dev/null
mkfs.btrfs -f $DEV
mount $DEV $MNT
bonnie++ -u root -d $MNT \
-n $NR_FILES:$DIRECTORY_SIZE:$DIRECTORY_SIZE:$NR_DIRECTORIES \
-r 0 -s $DATASET_SIZE -b
umount $MNT
Before patchset:
Version 2.00a ------Sequential Output------ --Sequential Input- --Random-
-Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Name:Size etc /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP
debian0 8G 376k 99 1.1g 98 939m 92 1527k 99 3.2g 99 9060 256
Latency 24920us 207us 680ms 5594us 171us 2891us
Version 2.00a ------Sequential Create------ --------Random Create--------
debian0 -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP
20/20 20480 96 +++++ +++ 20480 95 20480 99 +++++ +++ 20480 97
Latency 8708us 137us 5128us 6743us 60us 19712us
After patchset:
Version 2.00a ------Sequential Output------ --Sequential Input- --Random-
-Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Name:Size etc /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP
debian0 8G 384k 99 1.2g 99 971m 91 1533k 99 3.3g 99 9180 309
Latency 24930us 125us 661ms 5587us 46us 2020us
Version 2.00a ------Sequential Create------ --------Random Create--------
debian0 -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP
20/20 20480 90 +++++ +++ 20480 99 20480 99 +++++ +++ 20480 97
Latency 7030us 61us 1246us 4942us 56us 16855us
The patchset consists of this patch plus a previous one that has the
following subject:
"btrfs: avoid iterating over all indexes when logging directory"
Signed-off-by: Filipe Manana <fdmanana@suse.com>
---
fs/btrfs/tree-log.c | 51 +++++++++++++++++++++------------------------
1 file changed, 24 insertions(+), 27 deletions(-)
diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index c2a467276071..f298d7b03b8c 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -5428,45 +5428,34 @@ static int log_new_dir_dentries(struct btrfs_trans_handle *trans,
while (true) {
struct inode *vfs_inode;
- struct extent_buffer *leaf;
- struct btrfs_key min_key;
+ struct btrfs_key key;
+ struct btrfs_key found_key;
u64 next_index;
bool continue_curr_inode = true;
- int nritems;
- int i;
+ int iter_ret;
- min_key.objectid = ino;
- min_key.type = BTRFS_DIR_INDEX_KEY;
- min_key.offset = btrfs_get_first_dir_index_to_log(curr_inode);
- next_index = min_key.offset;
+ key.objectid = ino;
+ key.type = BTRFS_DIR_INDEX_KEY;
+ key.offset = btrfs_get_first_dir_index_to_log(curr_inode);
+ next_index = key.offset;
again:
- ret = btrfs_search_forward(root, &min_key, path, trans->transid);
- if (ret < 0) {
- break;
- } else if (ret > 0) {
- ret = 0;
- goto next;
- }
-
- leaf = path->nodes[0];
- nritems = btrfs_header_nritems(leaf);
- for (i = path->slots[0]; i < nritems; i++) {
+ btrfs_for_each_slot(root->log_root, &key, &found_key, path, iter_ret) {
+ struct extent_buffer *leaf = path->nodes[0];
struct btrfs_dir_item *di;
struct btrfs_key di_key;
struct inode *di_inode;
int log_mode = LOG_INODE_EXISTS;
int type;
- btrfs_item_key_to_cpu(leaf, &min_key, i);
- if (min_key.objectid != ino ||
- min_key.type != BTRFS_DIR_INDEX_KEY) {
+ if (found_key.objectid != ino ||
+ found_key.type != BTRFS_DIR_INDEX_KEY) {
continue_curr_inode = false;
break;
}
- next_index = min_key.offset + 1;
+ next_index = found_key.offset + 1;
- di = btrfs_item_ptr(leaf, i, struct btrfs_dir_item);
+ di = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_dir_item);
type = btrfs_dir_ftype(leaf, di);
if (btrfs_dir_transid(leaf, di) < trans->transid)
continue;
@@ -5508,12 +5497,20 @@ static int log_new_dir_dentries(struct btrfs_trans_handle *trans,
btrfs_release_path(path);
- if (continue_curr_inode && min_key.offset < (u64)-1) {
- min_key.offset++;
+ if (iter_ret < 0) {
+ ret = iter_ret;
+ goto out;
+ } else if (iter_ret > 0) {
+ continue_curr_inode = false;
+ } else {
+ key = found_key;
+ }
+
+ if (continue_curr_inode && key.offset < (u64)-1) {
+ key.offset++;
goto again;
}
-next:
btrfs_set_first_dir_index_to_log(curr_inode, next_index);
if (list_empty(&dir_list))
--
2.34.1
^ permalink raw reply related [flat|nested] 5+ messages in thread