[PATCH] O(1) sb list traversing on syncs
This patch removes O(n^2) super block loops in sync_inodes(),
sync_filesystems() etc. in favour of using __put_super_and_need_restart()
which I introduced earlier. We faced a noticably long freezes on sb
syncing when there are thousands of super blocks in the system.
Signed-Off-By: Kirill Korotaev <dev@sw.ru>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/fs/super.c b/fs/super.c
index 573bcc8..25bc1ec 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -341,20 +341,22 @@
*/
void sync_supers(void)
{
- struct super_block * sb;
-restart:
+ struct super_block *sb;
+
spin_lock(&sb_lock);
- sb = sb_entry(super_blocks.next);
- while (sb != sb_entry(&super_blocks))
+restart:
+ list_for_each_entry(sb, &super_blocks, s_list) {
if (sb->s_dirt) {
sb->s_count++;
spin_unlock(&sb_lock);
down_read(&sb->s_umount);
write_super(sb);
- drop_super(sb);
- goto restart;
- } else
- sb = sb_entry(sb->s_list.next);
+ up_read(&sb->s_umount);
+ spin_lock(&sb_lock);
+ if (__put_super_and_need_restart(sb))
+ goto restart;
+ }
+ }
spin_unlock(&sb_lock);
}
@@ -381,20 +383,16 @@
down(&mutex); /* Could be down_interruptible */
spin_lock(&sb_lock);
- for (sb = sb_entry(super_blocks.next); sb != sb_entry(&super_blocks);
- sb = sb_entry(sb->s_list.next)) {
+ list_for_each_entry(sb, &super_blocks, s_list) {
if (!sb->s_op->sync_fs)
continue;
if (sb->s_flags & MS_RDONLY)
continue;
sb->s_need_sync_fs = 1;
}
- spin_unlock(&sb_lock);
restart:
- spin_lock(&sb_lock);
- for (sb = sb_entry(super_blocks.next); sb != sb_entry(&super_blocks);
- sb = sb_entry(sb->s_list.next)) {
+ list_for_each_entry(sb, &super_blocks, s_list) {
if (!sb->s_need_sync_fs)
continue;
sb->s_need_sync_fs = 0;
@@ -405,8 +403,11 @@
down_read(&sb->s_umount);
if (sb->s_root && (wait || sb->s_dirt))
sb->s_op->sync_fs(sb, wait);
- drop_super(sb);
- goto restart;
+ up_read(&sb->s_umount);
+ /* restart only when sb is no longer on the list */
+ spin_lock(&sb_lock);
+ if (__put_super_and_need_restart(sb))
+ goto restart;
}
spin_unlock(&sb_lock);
up(&mutex);
@@ -422,21 +423,25 @@
struct super_block * get_super(struct block_device *bdev)
{
- struct list_head *p;
+ struct super_block *sb;
+
if (!bdev)
return NULL;
-rescan:
+
spin_lock(&sb_lock);
- list_for_each(p, &super_blocks) {
- struct super_block *s = sb_entry(p);
- if (s->s_bdev == bdev) {
- s->s_count++;
+rescan:
+ list_for_each_entry(sb, &super_blocks, s_list) {
+ if (sb->s_bdev == bdev) {
+ sb->s_count++;
spin_unlock(&sb_lock);
- down_read(&s->s_umount);
- if (s->s_root)
- return s;
- drop_super(s);
- goto rescan;
+ down_read(&sb->s_umount);
+ if (sb->s_root)
+ return sb;
+ up_read(&sb->s_umount);
+ /* restart only when sb is no longer on the list */
+ spin_lock(&sb_lock);
+ if (__put_super_and_need_restart(sb))
+ goto rescan;
}
}
spin_unlock(&sb_lock);
@@ -447,20 +452,22 @@
struct super_block * user_get_super(dev_t dev)
{
- struct list_head *p;
+ struct super_block *sb;
-rescan:
spin_lock(&sb_lock);
- list_for_each(p, &super_blocks) {
- struct super_block *s = sb_entry(p);
- if (s->s_dev == dev) {
- s->s_count++;
+rescan:
+ list_for_each_entry(sb, &super_blocks, s_list) {
+ if (sb->s_dev == dev) {
+ sb->s_count++;
spin_unlock(&sb_lock);
- down_read(&s->s_umount);
- if (s->s_root)
- return s;
- drop_super(s);
- goto rescan;
+ down_read(&sb->s_umount);
+ if (sb->s_root)
+ return sb;
+ up_read(&sb->s_umount);
+ /* restart only when sb is no longer on the list */
+ spin_lock(&sb_lock);
+ if (__put_super_and_need_restart(sb))
+ goto rescan;
}
}
spin_unlock(&sb_lock);
