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Date: Wed, 16 Feb 2022 15:25:23 -0800
From: harshad shirwadkar <harshadshirwadkar@...il.com>
To: Ritesh Harjani <riteshh@...ux.ibm.com>
Cc: Ext4 Developers List <linux-ext4@...r.kernel.org>,
"Theodore Ts'o" <tytso@....edu>, Jan Kara <jack@...e.com>,
Andreas Dilger <adilger.kernel@...ger.ca>,
linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC 1/1] ext4: Improve fast_commit performance and scalability
Thanks for the patch Ritesh. Some questions / comments inlined:
On Sun, 13 Feb 2022 at 19:57, Ritesh Harjani <riteshh@...ux.ibm.com> wrote:
>
> 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@...ux.ibm.com>
> ---
> fs/ext4/ext4.h | 2 ++
> fs/ext4/fast_commit.c | 64 +++++++++++++++++++++++++++++++------------
> fs/ext4/fast_commit.h | 1 +
> 3 files changed, 50 insertions(+), 17 deletions(-)
>
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index bcd3b9bf8069..25242648d8c9 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;
The only case in which this list will have multiple entries if hard
links are created on this inode right? I think that's probably a very
rare scenario and we can just fallback to full commits. That might
simplify this patch a bit. Basically if you do that then fc_dentry
would directly store a pointer to the inode and the inode can store a
pointer to the "CREAT" fc_dentry object. That way we don't have to do
list traversals in fc_del and fc_commit. But barring a few fixes, what
you have here is fine too. So I'll leave it up to you to decide what
you want to do.
> 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 7964ee34e322..f2bee4cf5648 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, *fc_dentry_n;
>
> 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;
> }
> @@ -295,7 +298,26 @@ void ext4_fc_del(struct inode *inode)
> ext4_fc_wait_committing_inode(inode);
> goto restart;
> }
> - list_del_init(&ei->i_fc_list);
> +
> + 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.
> + */
> + list_for_each_entry_safe(fc_dentry, fc_dentry_n, &ei->i_fc_dilist, 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);
> + 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;
Shouldn't we continue and remove all nodes in ei->i_fc_dilist?
> + }
> spin_unlock(&EXT4_SB(inode->i_sb)->s_fc_lock);
> }
>
> @@ -427,7 +449,7 @@ 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 +457,18 @@ 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)
> + list_add_tail(&node->fcd_dilist, &ei->i_fc_dilist);
> spin_unlock(&sbi->s_fc_lock);
> mutex_lock(&ei->i_fc_lock);
>
> @@ -954,7 +988,7 @@ __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 +1004,16 @@ __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_entry(fc_dentry->fcd_dilist.next,
> + struct ext4_inode_info, i_fc_dilist);
I think we want "fc_dentry->fcd_ilist.prev" here right? We are
sequentially traversing all the nodes in the list from first to last.
Given that I think the inode is the prev of any node that you
encounter in the list.
- Harshad
> + inode = &ei->vfs_inode;
> + WARN_ON(inode->i_ino != fc_dentry->fcd_ino);
> +
> spin_unlock(&sbi->s_fc_lock);
>
> /*
> @@ -1228,6 +1257,7 @@ 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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