[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/fs-writeback.c b/fs/fs-writeback.c
index 8e050fa..e94ab39 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -485,32 +485,6 @@
spin_unlock(&sb_lock);
}
-/*
- * Find a superblock with inodes that need to be synced
- */
-static struct super_block *get_super_to_sync(void)
-{
- struct super_block *sb;
-restart:
- spin_lock(&sb_lock);
- sb = sb_entry(super_blocks.prev);
- for (; sb != sb_entry(&super_blocks); sb = sb_entry(sb->s_list.prev)) {
- if (sb->s_syncing)
- continue;
- sb->s_syncing = 1;
- sb->s_count++;
- spin_unlock(&sb_lock);
- down_read(&sb->s_umount);
- if (!sb->s_root) {
- drop_super(sb);
- goto restart;
- }
- return sb;
- }
- spin_unlock(&sb_lock);
- return NULL;
-}
-
/**
* sync_inodes - writes all inodes to disk
* @wait: wait for completion
@@ -530,23 +504,39 @@
* outstanding dirty inodes, the writeback goes block-at-a-time within the
* filesystem's write_inode(). This is extremely slow.
*/
-void sync_inodes(int wait)
+static void __sync_inodes(int wait)
{
struct super_block *sb;
- set_sb_syncing(0);
- while ((sb = get_super_to_sync()) != NULL) {
- sync_inodes_sb(sb, 0);
- sync_blockdev(sb->s_bdev);
- drop_super(sb);
+ spin_lock(&sb_lock);
+restart:
+ list_for_each_entry(sb, &super_blocks, s_list) {
+ if (sb->s_syncing)
+ continue;
+ sb->s_syncing = 1;
+ sb->s_count++;
+ spin_unlock(&sb_lock);
+ down_read(&sb->s_umount);
+ if (sb->s_root) {
+ sync_inodes_sb(sb, wait);
+ sync_blockdev(sb->s_bdev);
+ }
+ up_read(&sb->s_umount);
+ spin_lock(&sb_lock);
+ if (__put_super_and_need_restart(sb))
+ goto restart;
}
+ spin_unlock(&sb_lock);
+}
+
+void sync_inodes(int wait)
+{
+ set_sb_syncing(0);
+ __sync_inodes(0);
+
if (wait) {
set_sb_syncing(0);
- while ((sb = get_super_to_sync()) != NULL) {
- sync_inodes_sb(sb, 1);
- sync_blockdev(sb->s_bdev);
- drop_super(sb);
- }
+ __sync_inodes(1);
}
}