[PATCH v9 3/5] vfs: Use dlock list for superblock's inode list

From: Waiman Long
Date: Wed Sep 12 2018 - 15:29:25 EST

When many threads are trying to add or delete inode to or from
a superblock's s_inodes list, spinlock contention on the list can
become a performance bottleneck.

This patch changes the s_inodes field to become a dlock list which
is a distributed set of lists with per-list spinlocks. As a result,
the following superblock inode list (sb->s_inodes) iteration functions
in vfs are also being modified:

1. iterate_bdevs()
2. drop_pagecache_sb()
3. evict_inodes()
4. invalidate_inodes()
5. fsnotify_unmount_inodes()
6. add_dquot_ref()
7. remove_dquot_ref()

With an exit microbenchmark that creates a large number of threads,
attachs many inodes to them in procfs and then exits. The runtimes of
that microbenchmark with various number of threads before and after
the patch on a 4-socket Intel E7-8867 v3 system (64 cores, 128 threads)
on a 4.19-rc3 based kernel were as follows:

# of threads Elapsed/Sys Time Elapsed/Sys Time Speedup
Unpatched Kernel Patched Kernel
------------ ---------------- ---------------- -------
1000 59.17s/123m09.8s 18.90s/24m44.5s 3.13
1200 73.20s/151m24.1s 27.54s/50m05.3s 2.66
1400 102.04s/212m00.9s 36.75s/68m26.7s 2.78
1600 131.13s/272m52.4s 50.16s/94m23.7s 2.61

Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
Reviewed-by: Jan Kara <jack@xxxxxxx>
---
fs/block_dev.c | 9 ++++-----
fs/drop_caches.c | 9 ++++-----
fs/inode.c | 34 +++++++++++++---------------------
fs/notify/fsnotify.c | 9 ++++-----
fs/quota/dquot.c | 14 ++++++--------
fs/super.c | 7 ++++---
include/linux/fs.h | 8 ++++----
7 files changed, 39 insertions(+), 51 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 38b8ce0..7f596241 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -2133,9 +2133,9 @@ int __invalidate_device(struct block_device *bdev, bool kill_dirty)
void iterate_bdevs(void (*func)(struct block_device *, void *), void *arg)
{
struct inode *inode, *old_inode = NULL;
+ DEFINE_DLOCK_LIST_ITER(iter, &blockdev_superblock->s_inodes);

- spin_lock(&blockdev_superblock->s_inode_list_lock);
- list_for_each_entry(inode, &blockdev_superblock->s_inodes, i_sb_list) {
+ dlist_for_each_entry(inode, &iter, i_sb_list) {
struct address_space *mapping = inode->i_mapping;
struct block_device *bdev;

@@ -2147,7 +2147,7 @@ void iterate_bdevs(void (*func)(struct block_device *, void *), void *arg)
}
__iget(inode);
spin_unlock(&inode->i_lock);
- spin_unlock(&blockdev_superblock->s_inode_list_lock);
+ dlock_list_unlock(&iter);
/*
* We hold a reference to 'inode' so it couldn't have been
* removed from s_inodes list while we dropped the
@@ -2165,8 +2165,7 @@ void iterate_bdevs(void (*func)(struct block_device *, void *), void *arg)
func(bdev, arg);
mutex_unlock(&bdev->bd_mutex);

- spin_lock(&blockdev_superblock->s_inode_list_lock);
+ dlock_list_relock(&iter);
}
- spin_unlock(&blockdev_superblock->s_inode_list_lock);
iput(old_inode);
}
diff --git a/fs/drop_caches.c b/fs/drop_caches.c
index 8237701..7ddd5bb 100644
--- a/fs/drop_caches.c
+++ b/fs/drop_caches.c
@@ -17,9 +17,9 @@
static void drop_pagecache_sb(struct super_block *sb, void *unused)
{
struct inode *inode, *toput_inode = NULL;
+ DEFINE_DLOCK_LIST_ITER(iter, &sb->s_inodes);

- spin_lock(&sb->s_inode_list_lock);
- list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
+ dlist_for_each_entry(inode, &iter, i_sb_list) {
spin_lock(&inode->i_lock);
if ((inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) ||
(inode->i_mapping->nrpages == 0)) {
@@ -28,15 +28,14 @@ static void drop_pagecache_sb(struct super_block *sb, void *unused)
}
__iget(inode);
spin_unlock(&inode->i_lock);
- spin_unlock(&sb->s_inode_list_lock);
+ dlock_list_unlock(&iter);

invalidate_mapping_pages(inode->i_mapping, 0, -1);
iput(toput_inode);
toput_inode = inode;

- spin_lock(&sb->s_inode_list_lock);
+ dlock_list_relock(&iter);
}
- spin_unlock(&sb->s_inode_list_lock);
iput(toput_inode);
}

diff --git a/fs/inode.c b/fs/inode.c
index 0b5381b..a99e045 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -29,7 +29,7 @@
* inode->i_state, inode->i_hash, __iget()
* Inode LRU list locks protect:
* inode->i_sb->s_inode_lru, inode->i_lru
- * inode->i_sb->s_inode_list_lock protects:
+ * inode->i_sb->s_inodes->head->lock protects:
* inode->i_sb->s_inodes, inode->i_sb_list
* bdi->wb.list_lock protects:
* bdi->wb.b_{dirty,io,more_io,dirty_time}, inode->i_io_list
@@ -38,7 +38,7 @@
*
* Lock ordering:
*
- * inode->i_sb->s_inode_list_lock
+ * inode->i_sb->s_inodes->head->lock
* inode->i_lock
* Inode LRU list locks
*
@@ -46,7 +46,7 @@
* inode->i_lock
*
* inode_hash_lock
- * inode->i_sb->s_inode_list_lock
+ * inode->i_sb->s_inodes->head->lock
* inode->i_lock
*
* iunique_lock
@@ -440,19 +440,14 @@ static void inode_lru_list_del(struct inode *inode)
*/
void inode_sb_list_add(struct inode *inode)
{
- spin_lock(&inode->i_sb->s_inode_list_lock);
- list_add(&inode->i_sb_list, &inode->i_sb->s_inodes);
- spin_unlock(&inode->i_sb->s_inode_list_lock);
+ dlock_lists_add(&inode->i_sb_list, &inode->i_sb->s_inodes);
}
EXPORT_SYMBOL_GPL(inode_sb_list_add);

static inline void inode_sb_list_del(struct inode *inode)
{
- if (!list_empty(&inode->i_sb_list)) {
- spin_lock(&inode->i_sb->s_inode_list_lock);
- list_del_init(&inode->i_sb_list);
- spin_unlock(&inode->i_sb->s_inode_list_lock);
- }
+ if (!list_empty(&inode->i_sb_list.list))
+ dlock_lists_del(&inode->i_sb_list);
}

static unsigned long hash(struct super_block *sb, unsigned long hashval)
@@ -607,11 +602,12 @@ static void dispose_list(struct list_head *head)
void evict_inodes(struct super_block *sb)
{
struct inode *inode;
+ struct dlock_list_iter iter;
LIST_HEAD(dispose);

again:
- spin_lock(&sb->s_inode_list_lock);
- list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
+ init_dlock_list_iter(&iter, &sb->s_inodes);
+ dlist_for_each_entry(inode, &iter, i_sb_list) {
if (atomic_read(&inode->i_count))
continue;

@@ -632,13 +628,12 @@ void evict_inodes(struct super_block *sb)
* bit so we don't livelock.
*/
if (need_resched()) {
- spin_unlock(&sb->s_inode_list_lock);
+ dlock_list_unlock(&iter);
cond_resched();
dispose_list(&dispose);
goto again;
}
}
- spin_unlock(&sb->s_inode_list_lock);

dispose_list(&dispose);
}
@@ -659,9 +654,9 @@ int invalidate_inodes(struct super_block *sb, bool kill_dirty)
int busy = 0;
struct inode *inode;
LIST_HEAD(dispose);
+ DEFINE_DLOCK_LIST_ITER(iter, &sb->s_inodes);

- spin_lock(&sb->s_inode_list_lock);
- list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
+ dlist_for_each_entry(inode, &iter, i_sb_list) {
spin_lock(&inode->i_lock);
if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
spin_unlock(&inode->i_lock);
@@ -683,7 +678,6 @@ int invalidate_inodes(struct super_block *sb, bool kill_dirty)
spin_unlock(&inode->i_lock);
list_add(&inode->i_lru, &dispose);
}
- spin_unlock(&sb->s_inode_list_lock);

dispose_list(&dispose);

@@ -906,7 +900,7 @@ struct inode *new_inode_pseudo(struct super_block *sb)
spin_lock(&inode->i_lock);
inode->i_state = 0;
spin_unlock(&inode->i_lock);
- INIT_LIST_HEAD(&inode->i_sb_list);
+ init_dlock_list_node(&inode->i_sb_list);
}
return inode;
}
@@ -927,8 +921,6 @@ struct inode *new_inode(struct super_block *sb)
{
struct inode *inode;

- spin_lock_prefetch(&sb->s_inode_list_lock);
-
inode = new_inode_pseudo(sb);
if (inode)
inode_sb_list_add(inode);
diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
index ababdbf..0c9084b 100644
--- a/fs/notify/fsnotify.c
+++ b/fs/notify/fsnotify.c
@@ -51,9 +51,9 @@ void __fsnotify_vfsmount_delete(struct vfsmount *mnt)
void fsnotify_unmount_inodes(struct super_block *sb)
{
struct inode *inode, *iput_inode = NULL;
+ DEFINE_DLOCK_LIST_ITER(iter, &sb->s_inodes);

- spin_lock(&sb->s_inode_list_lock);
- list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
+ dlist_for_each_entry(inode, &iter, i_sb_list) {
/*
* We cannot __iget() an inode in state I_FREEING,
* I_WILL_FREE, or I_NEW which is fine because by that point
@@ -78,7 +78,7 @@ void fsnotify_unmount_inodes(struct super_block *sb)

__iget(inode);
spin_unlock(&inode->i_lock);
- spin_unlock(&sb->s_inode_list_lock);
+ dlock_list_unlock(&iter);

if (iput_inode)
iput(iput_inode);
@@ -90,9 +90,8 @@ void fsnotify_unmount_inodes(struct super_block *sb)

iput_inode = inode;

- spin_lock(&sb->s_inode_list_lock);
+ dlock_list_relock(&iter);
}
- spin_unlock(&sb->s_inode_list_lock);

if (iput_inode)
iput(iput_inode);
diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
index fc20e06..2cd91d7 100644
--- a/fs/quota/dquot.c
+++ b/fs/quota/dquot.c
@@ -941,13 +941,13 @@ static int dqinit_needed(struct inode *inode, int type)
static int add_dquot_ref(struct super_block *sb, int type)
{
struct inode *inode, *old_inode = NULL;
+ DEFINE_DLOCK_LIST_ITER(iter, &sb->s_inodes);
#ifdef CONFIG_QUOTA_DEBUG
int reserved = 0;
#endif
int err = 0;

- spin_lock(&sb->s_inode_list_lock);
- list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
+ dlist_for_each_entry(inode, &iter, i_sb_list) {
spin_lock(&inode->i_lock);
if ((inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) ||
!atomic_read(&inode->i_writecount) ||
@@ -957,7 +957,7 @@ static int add_dquot_ref(struct super_block *sb, int type)
}
__iget(inode);
spin_unlock(&inode->i_lock);
- spin_unlock(&sb->s_inode_list_lock);
+ dlock_list_unlock(&iter);

#ifdef CONFIG_QUOTA_DEBUG
if (unlikely(inode_get_rsv_space(inode) > 0))
@@ -979,9 +979,8 @@ static int add_dquot_ref(struct super_block *sb, int type)
* later.
*/
old_inode = inode;
- spin_lock(&sb->s_inode_list_lock);
+ dlock_list_relock(&iter);
}
- spin_unlock(&sb->s_inode_list_lock);
iput(old_inode);
out:
#ifdef CONFIG_QUOTA_DEBUG
@@ -1050,9 +1049,9 @@ static void remove_dquot_ref(struct super_block *sb, int type,
{
struct inode *inode;
int reserved = 0;
+ DEFINE_DLOCK_LIST_ITER(iter, &sb->s_inodes);

- spin_lock(&sb->s_inode_list_lock);
- list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
+ dlist_for_each_entry(inode, &iter, i_sb_list) {
/*
* We have to scan also I_NEW inodes because they can already
* have quota pointer initialized. Luckily, we need to touch
@@ -1067,7 +1066,6 @@ static void remove_dquot_ref(struct super_block *sb, int type,
}
spin_unlock(&dq_data_lock);
}
- spin_unlock(&sb->s_inode_list_lock);
#ifdef CONFIG_QUOTA_DEBUG
if (reserved) {
printk(KERN_WARNING "VFS (%s): Writes happened after quota"
diff --git a/fs/super.c b/fs/super.c
index f3a8c00..dbbe96a 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -177,6 +177,7 @@ static void destroy_unused_super(struct super_block *s)
up_write(&s->s_umount);
list_lru_destroy(&s->s_dentry_lru);
list_lru_destroy(&s->s_inode_lru);
+ free_dlock_list_heads(&s->s_inodes);
security_sb_free(s);
put_user_ns(s->s_user_ns);
kfree(s->s_subtype);
@@ -242,8 +243,6 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags,
INIT_HLIST_NODE(&s->s_instances);
INIT_HLIST_BL_HEAD(&s->s_roots);
mutex_init(&s->s_sync_lock);
- INIT_LIST_HEAD(&s->s_inodes);
- spin_lock_init(&s->s_inode_list_lock);
INIT_LIST_HEAD(&s->s_inodes_wb);
spin_lock_init(&s->s_inode_wblist_lock);

@@ -262,6 +261,8 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags,
s->s_shrink.count_objects = super_cache_count;
s->s_shrink.batch = 1024;
s->s_shrink.flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE;
+ if (alloc_dlock_list_heads(&s->s_inodes))
+ goto fail;
if (prealloc_shrinker(&s->s_shrink))
goto fail;
if (list_lru_init_memcg(&s->s_dentry_lru, &s->s_shrink))
@@ -455,7 +456,7 @@ void generic_shutdown_super(struct super_block *sb)
if (sop->put_super)
sop->put_super(sb);

- if (!list_empty(&sb->s_inodes)) {
+ if (!dlock_lists_empty(&sb->s_inodes)) {
printk("VFS: Busy inodes after unmount of %s. "
"Self-destruct in 5 seconds. Have a nice day...\n",
sb->s_id);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 3332270..6f84731 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -37,6 +37,7 @@
#include <linux/uuid.h>
#include <linux/errseq.h>
#include <linux/ioprio.h>
+#include <linux/dlock-list.h>

#include <asm/byteorder.h>
#include <uapi/linux/fs.h>
@@ -647,7 +648,7 @@ struct inode {
u16 i_wb_frn_history;
#endif
struct list_head i_lru; /* inode LRU list */
- struct list_head i_sb_list;
+ struct dlock_list_node i_sb_list;
struct list_head i_wb_list; /* backing dev writeback list */
union {
struct hlist_head i_dentry;
@@ -1458,9 +1459,8 @@ struct super_block {
*/
int s_stack_depth;

- /* s_inode_list_lock protects s_inodes */
- spinlock_t s_inode_list_lock ____cacheline_aligned_in_smp;
- struct list_head s_inodes; /* all inodes */
+ /* The internal per-list locks protect s_inodes */
+ struct dlock_list_heads s_inodes; /* all inodes */

spinlock_t s_inode_wblist_lock;
struct list_head s_inodes_wb; /* writeback inodes */
--
1.8.3.1