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Subject[PATCH 1/3] fput: turn "list_head delayed_fput_list" into llist_head
fput() and delayed_fput() can use llist and avoid the locking.

This is unlikely path, it is not that this change can improve
the performance, but this way the code looks simpler.

Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
fs/file_table.c | 25 ++++++++++---------------
include/linux/fs.h | 2 ++
2 files changed, 12 insertions(+), 15 deletions(-)

diff --git a/fs/file_table.c b/fs/file_table.c
index 3a2bbc5..94b1bfa 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -265,18 +265,15 @@ static void __fput(struct file *file)
mntput(mnt);
}

-static DEFINE_SPINLOCK(delayed_fput_lock);
-static LIST_HEAD(delayed_fput_list);
+static LLIST_HEAD(delayed_fput_list);
static void delayed_fput(struct work_struct *unused)
{
- LIST_HEAD(head);
- spin_lock_irq(&delayed_fput_lock);
- list_splice_init(&delayed_fput_list, &head);
- spin_unlock_irq(&delayed_fput_lock);
- while (!list_empty(&head)) {
- struct file *f = list_first_entry(&head, struct file, f_u.fu_list);
- list_del_init(&f->f_u.fu_list);
- __fput(f);
+ struct llist_node *node = llist_del_all(&delayed_fput_list);
+ struct llist_node *next;
+
+ for (; node; node = next) {
+ next = llist_next(node);
+ __fput(llist_entry(node, struct file, f_u.fu_llist));
}
}

@@ -306,7 +303,6 @@ void fput(struct file *file)
{
if (atomic_long_dec_and_test(&file->f_count)) {
struct task_struct *task = current;
- unsigned long flags;

file_sb_list_del(file);
if (likely(!in_interrupt() && !(task->flags & PF_KTHREAD))) {
@@ -320,10 +316,9 @@ void fput(struct file *file)
* fput to avoid leaking *file.
*/
}
- spin_lock_irqsave(&delayed_fput_lock, flags);
- list_add(&file->f_u.fu_list, &delayed_fput_list);
- schedule_work(&delayed_fput_work);
- spin_unlock_irqrestore(&delayed_fput_lock, flags);
+
+ if (llist_add(&file->f_u.fu_llist, &delayed_fput_list))
+ schedule_work(&delayed_fput_work);
}
}

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 43db02e..8a60d99 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -10,6 +10,7 @@
#include <linux/stat.h>
#include <linux/cache.h>
#include <linux/list.h>
+#include <linux/llist.h>
#include <linux/radix-tree.h>
#include <linux/rbtree.h>
#include <linux/init.h>
@@ -767,6 +768,7 @@ struct file {
*/
union {
struct list_head fu_list;
+ struct llist_node fu_llist;
struct rcu_head fu_rcuhead;
} f_u;
struct path f_path;
--
1.5.5.1


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