[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>

1 files changed, 24 insertions, 36 deletions

diff --git a/fs/quota.c b/fs/quota.c
index 3f0333a51a23..f5d1cff55196 100644
--- a/fs/quota.c
+++ b/fs/quota.c
@@ -149,36 +149,6 @@ static int check_quotactl_valid(struct super_block *sb, int type, int cmd, qid_t
         return error;
 }
 
-static struct super_block *get_super_to_sync(int type)
-{
-        struct list_head *head;
-        int cnt, dirty;
-
-restart:
-        spin_lock(&sb_lock);
-        list_for_each(head, &super_blocks) {
-                struct super_block *sb = list_entry(head, struct super_block, s_list);
-
-                /* This test just improves performance so it needn't be reliable... */
-                for (cnt = 0, dirty = 0; cnt < MAXQUOTAS; cnt++)
-                        if ((type == cnt || type == -1) && sb_has_quota_enabled(sb, cnt)
-                            && info_any_dirty(&sb_dqopt(sb)->info[cnt]))
-                                dirty = 1;
-                if (!dirty)
-                        continue;
-                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;
-}
-
 static void quota_sync_sb(struct super_block *sb, int type)
 {
         int cnt;
@@ -219,17 +189,35 @@ static void quota_sync_sb(struct super_block *sb, int type)
 
 void sync_dquots(struct super_block *sb, int type)
 {
+        int cnt, dirty;
+
         if (sb) {
                 if (sb->s_qcop->quota_sync)
                         quota_sync_sb(sb, type);
+                return;
         }
-        else {
-                while ((sb = get_super_to_sync(type)) != NULL) {
-                        if (sb->s_qcop->quota_sync)
-                                quota_sync_sb(sb, type);
-                        drop_super(sb);
-                }
+
+        spin_lock(&sb_lock);
+restart:
+        list_for_each_entry(sb, &super_blocks, s_list) {
+                /* This test just improves performance so it needn't be reliable... */
+                for (cnt = 0, dirty = 0; cnt < MAXQUOTAS; cnt++)
+                        if ((type == cnt || type == -1) && sb_has_quota_enabled(sb, cnt)
+                            && info_any_dirty(&sb_dqopt(sb)->info[cnt]))
+                                dirty = 1;
+                if (!dirty)
+                        continue;
+                sb->s_count++;
+                spin_unlock(&sb_lock);
+                down_read(&sb->s_umount);
+                if (sb->s_root && sb->s_qcop->quota_sync)
+                        quota_sync_sb(sb, type);
+                up_read(&sb->s_umount);
+                spin_lock(&sb_lock);
+                if (__put_super_and_need_restart(sb))
+                        goto restart;
         }
+        spin_unlock(&sb_lock);
 }
 
 /* Copy parameters and call proper function */