[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/quota.c b/fs/quota.c
index 3f0333a..f5d1cff 100644
--- a/fs/quota.c
+++ b/fs/quota.c
@@ -149,36 +149,6 @@
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 @@
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 */