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Subject[PATCHv2 1/1] ext4: Improve fast_commit performance and scalability
Date
Currently ext4_fc_commit_dentry_updates() is of quadratic time
complexity, which is causing performance bottlenecks with high
threads/file/dir count with fs_mark.

This patch makes commit dentry updates (and hence ext4_fc_commit()) path
to linear time complexity. Hence improves the performance of workloads
which does fsync on multiple threads/open files one-by-one.

Absolute numbers in avg file creates per sec (from fs_mark in 1K order)
=======================================================================
no. Order without-patch(K) with-patch(K) Diff(%)
1 1 16.90 17.51 +3.60
2 2,2 32.08 31.80 -0.87
3 3,3 53.97 55.01 +1.92
4 4,4 78.94 76.90 -2.58
5 5,5 95.82 95.37 -0.46
6 6,6 87.92 103.38 +17.58
7 6,10 0.73 126.13 +17178.08
8 6,14 2.33 143.19 +6045.49

workload type
==============
For e.g. 7th row order of 6,10 (2^6 == 64 && 2^10 == 1024)
echo /run/riteshh/mnt/{1..64} |sed -E 's/[[:space:]]+/ -d /g' \
| xargs -I {} bash -c "sudo fs_mark -L 100 -D 1024 -n 1024 -s0 -S5 -d {}"

Perf profile
(w/o patches)
=============================
87.15% [kernel] [k] ext4_fc_commit --> Heavy contention/bottleneck
1.98% [kernel] [k] perf_event_interrupt
0.96% [kernel] [k] power_pmu_enable
0.91% [kernel] [k] update_sd_lb_stats.constprop.0
0.67% [kernel] [k] ktime_get

Signed-off-by: Ritesh Harjani <riteshh@linux.ibm.com>
---
fs/ext4/ext4.h | 2 ++
fs/ext4/fast_commit.c | 74 ++++++++++++++++++++++++++++++++-----------
fs/ext4/fast_commit.h | 1 +
3 files changed, 59 insertions(+), 18 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 0d4f284c0514..3f87cca49f0c 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1046,6 +1046,8 @@ struct ext4_inode_info {

/* Fast commit related info */

+ /* For tracking dentry create updates */
+ struct list_head i_fc_dilist;
struct list_head i_fc_list; /*
* inodes that need fast commit
* protected by sbi->s_fc_lock.
diff --git a/fs/ext4/fast_commit.c b/fs/ext4/fast_commit.c
index 3c5baca38767..5ac594e03402 100644
--- a/fs/ext4/fast_commit.c
+++ b/fs/ext4/fast_commit.c
@@ -199,6 +199,7 @@ void ext4_fc_init_inode(struct inode *inode)
ext4_fc_reset_inode(inode);
ext4_clear_inode_state(inode, EXT4_STATE_FC_COMMITTING);
INIT_LIST_HEAD(&ei->i_fc_list);
+ INIT_LIST_HEAD(&ei->i_fc_dilist);
init_waitqueue_head(&ei->i_fc_wait);
atomic_set(&ei->i_fc_updates, 0);
}
@@ -279,6 +280,8 @@ void ext4_fc_stop_update(struct inode *inode)
void ext4_fc_del(struct inode *inode)
{
struct ext4_inode_info *ei = EXT4_I(inode);
+ struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
+ struct ext4_fc_dentry_update *fc_dentry;

if (!test_opt2(inode->i_sb, JOURNAL_FAST_COMMIT) ||
(EXT4_SB(inode->i_sb)->s_mount_state & EXT4_FC_REPLAY))
@@ -286,7 +289,7 @@ void ext4_fc_del(struct inode *inode)

restart:
spin_lock(&EXT4_SB(inode->i_sb)->s_fc_lock);
- if (list_empty(&ei->i_fc_list)) {
+ if (list_empty(&ei->i_fc_list) && list_empty(&ei->i_fc_dilist)) {
spin_unlock(&EXT4_SB(inode->i_sb)->s_fc_lock);
return;
}
@@ -295,8 +298,33 @@ void ext4_fc_del(struct inode *inode)
ext4_fc_wait_committing_inode(inode);
goto restart;
}
- list_del_init(&ei->i_fc_list);
- spin_unlock(&EXT4_SB(inode->i_sb)->s_fc_lock);
+
+ if (!list_empty(&ei->i_fc_list))
+ list_del_init(&ei->i_fc_list);
+
+ /*
+ * Since this inode is getting removed, let's also remove all FC
+ * dentry create references, since it is not needed to log it anyways.
+ */
+ if (list_empty(&ei->i_fc_dilist)) {
+ spin_unlock(&sbi->s_fc_lock);
+ return;
+ }
+
+ fc_dentry = list_first_entry(&ei->i_fc_dilist, struct ext4_fc_dentry_update, fcd_dilist);
+ WARN_ON(fc_dentry->fcd_op != EXT4_FC_TAG_CREAT);
+ list_del_init(&fc_dentry->fcd_list);
+ list_del_init(&fc_dentry->fcd_dilist);
+
+ WARN_ON(!list_empty(&ei->i_fc_dilist));
+ spin_unlock(&sbi->s_fc_lock);
+
+ if (fc_dentry->fcd_name.name &&
+ fc_dentry->fcd_name.len > DNAME_INLINE_LEN)
+ kfree(fc_dentry->fcd_name.name);
+ kmem_cache_free(ext4_fc_dentry_cachep, fc_dentry);
+
+ return;
}

/*
@@ -427,7 +455,7 @@ static int __track_dentry_update(struct inode *inode, void *arg, bool update)
node->fcd_name.name = node->fcd_iname;
}
node->fcd_name.len = dentry->d_name.len;
-
+ INIT_LIST_HEAD(&node->fcd_dilist);
spin_lock(&sbi->s_fc_lock);
if (sbi->s_journal->j_flags & JBD2_FULL_COMMIT_ONGOING ||
sbi->s_journal->j_flags & JBD2_FAST_COMMIT_ONGOING)
@@ -435,6 +463,20 @@ static int __track_dentry_update(struct inode *inode, void *arg, bool update)
&sbi->s_fc_dentry_q[FC_Q_STAGING]);
else
list_add_tail(&node->fcd_list, &sbi->s_fc_dentry_q[FC_Q_MAIN]);
+
+ /*
+ * This helps us keep a track of all fc_dentry updates which is part of
+ * this ext4 inode. So in case the inode is getting unlinked, before
+ * even we get a chance to fsync, we could remove all fc_dentry
+ * references while evicting the inode in ext4_fc_del().
+ * Also with this, we don't need to loop over all the inodes in
+ * sbi->s_fc_q to get the corresponding inode in
+ * ext4_fc_commit_dentry_updates().
+ */
+ if (dentry_update->op == EXT4_FC_TAG_CREAT) {
+ WARN_ON(!list_empty(&ei->i_fc_dilist));
+ list_add_tail(&node->fcd_dilist, &ei->i_fc_dilist);
+ }
spin_unlock(&sbi->s_fc_lock);
mutex_lock(&ei->i_fc_lock);

@@ -954,7 +996,7 @@ __releases(&sbi->s_fc_lock)
struct ext4_sb_info *sbi = EXT4_SB(sb);
struct ext4_fc_dentry_update *fc_dentry, *fc_dentry_n;
struct inode *inode;
- struct ext4_inode_info *ei, *ei_n;
+ struct ext4_inode_info *ei;
int ret;

if (list_empty(&sbi->s_fc_dentry_q[FC_Q_MAIN]))
@@ -970,21 +1012,16 @@ __releases(&sbi->s_fc_lock)
spin_lock(&sbi->s_fc_lock);
continue;
}
-
- inode = NULL;
- list_for_each_entry_safe(ei, ei_n, &sbi->s_fc_q[FC_Q_MAIN],
- i_fc_list) {
- if (ei->vfs_inode.i_ino == fc_dentry->fcd_ino) {
- inode = &ei->vfs_inode;
- break;
- }
- }
/*
- * If we don't find inode in our list, then it was deleted,
- * in which case, we don't need to record it's create tag.
+ * With fcd_dilist we need not loop in sbi->s_fc_q to get the
+ * corresponding inode pointer
*/
- if (!inode)
- continue;
+ WARN_ON(list_empty(&fc_dentry->fcd_dilist));
+ ei = list_first_entry(&fc_dentry->fcd_dilist,
+ struct ext4_inode_info, i_fc_dilist);
+ inode = &ei->vfs_inode;
+ WARN_ON(inode->i_ino != fc_dentry->fcd_ino);
+
spin_unlock(&sbi->s_fc_lock);

/*
@@ -1228,6 +1265,7 @@ static void ext4_fc_cleanup(journal_t *journal, int full, tid_t tid)
struct ext4_fc_dentry_update,
fcd_list);
list_del_init(&fc_dentry->fcd_list);
+ list_del_init(&fc_dentry->fcd_dilist);
spin_unlock(&sbi->s_fc_lock);

if (fc_dentry->fcd_name.name &&
diff --git a/fs/ext4/fast_commit.h b/fs/ext4/fast_commit.h
index 083ad1cb705a..02afa52e8e41 100644
--- a/fs/ext4/fast_commit.h
+++ b/fs/ext4/fast_commit.h
@@ -109,6 +109,7 @@ struct ext4_fc_dentry_update {
struct qstr fcd_name; /* Dirent name */
unsigned char fcd_iname[DNAME_INLINE_LEN]; /* Dirent name string */
struct list_head fcd_list;
+ struct list_head fcd_dilist;
};

struct ext4_fc_stats {
--
2.31.1
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