Commit b3998b3b authored by Ritesh Harjani's avatar Ritesh Harjani Committed by Theodore Ts'o
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ext4: improve fast_commit performance and scalability 



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: default avatarRitesh Harjani <riteshh@linux.ibm.com>
Reviewed-by: default avatarHarshad Shirwadkar <harshadshirwadkar@gmail.com>
Link: https://lore.kernel.org/r/930f35d4fd5f83e2673c868781d9ebf15e91bf4e.1645426817.git.riteshh@linux.ibm.com


Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
parent 8c91c579

fs/ext4/ext4.h

+2 −0
Original line number Diff line number Diff line
@@ -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.

fs/ext4/fast_commit.c

+56 −18
Original line number Diff line number Diff line
@@ -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;

	}



	if (!list_empty(&ei->i_fc_list))

		list_del_init(&ei->i_fc_list);

	spin_unlock(&EXT4_SB(inode->i_sb)->s_fc_lock);



	/*

	 * 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 &&

fs/ext4/fast_commit.h

+1 −0
Original line number Diff line number Diff line
@@ -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 {