From fa4b8cb1738097586f49ec66cd3656cef47ac143 Mon Sep 17 00:00:00 2001 From: Filipe Manana Date: Wed, 5 Apr 2023 18:51:29 +0100 Subject: [PATCH] btrfs: avoid iterating over all indexes when logging directory 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 Signed-off-by: David Sterba --- fs/btrfs/btrfs_inode.h | 32 +++++++++++++++++++++++++++----- fs/btrfs/tree-log.c | 32 ++++++++++++++++++++++++++++++-- 2 files changed, 57 insertions(+), 7 deletions(-) diff --git a/fs/btrfs/btrfs_inode.h b/fs/btrfs/btrfs_inode.h index bb49844..ec2ae44 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 f6c3f14..d746ebf 100644 --- a/fs/btrfs/tree-log.c +++ b/fs/btrfs/tree-log.c @@ -3618,6 +3618,9 @@ 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); @@ -5376,6 +5379,7 @@ 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; /* @@ -5390,18 +5394,23 @@ static int log_new_dir_dentries(struct btrfs_trans_handle *trans, if (!path) return -ENOMEM; + /* Pairs with btrfs_add_delayed_iput below. */ + 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; @@ -5426,6 +5435,8 @@ again: 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) @@ -5466,12 +5477,16 @@ again: 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; @@ -5479,9 +5494,22 @@ next: 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; -- 2.7.4