quota: move code from sync_quota_sb into vfs_quota_sync

Currenly sync_quota_sb does a lot of sync and truncate action that only
applies to "VFS" style quotas and is actively harmful for the sync
performance in XFS.  Move it into vfs_quota_sync and add a wait parameter
to ->quota_sync to tell if we need it or not.

My audit of the GFS2 code says it's also not needed given the way GFS2
implements quotas, but I'd be happy if this can get a detailed review.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jan Kara <jack@suse.cz>

1 files changed, 28 insertions, 1 deletions

diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
index 6c849de5dc8f..4c2213f7ed36 100644
--- a/fs/quota/dquot.c
+++ b/fs/quota/dquot.c
@@ -570,7 +570,7 @@ out:
 }
 EXPORT_SYMBOL(dquot_scan_active);
 
-int vfs_quota_sync(struct super_block *sb, int type)
+int vfs_quota_sync(struct super_block *sb, int type, int wait)
 {
 	struct list_head *dirty;
 	struct dquot *dquot;
@@ -615,6 +615,33 @@ int vfs_quota_sync(struct super_block *sb, int type)
 	spin_unlock(&dq_list_lock);
 	mutex_unlock(&dqopt->dqonoff_mutex);
 
+	if (!wait || (sb_dqopt(sb)->flags & DQUOT_QUOTA_SYS_FILE))
+		return 0;
+
+	/* This is not very clever (and fast) but currently I don't know about
+	 * any other simple way of getting quota data to disk and we must get
+	 * them there for userspace to be visible... */
+	if (sb->s_op->sync_fs)
+		sb->s_op->sync_fs(sb, 1);
+	sync_blockdev(sb->s_bdev);
+
+	/*
+	 * Now when everything is written we can discard the pagecache so
+	 * that userspace sees the changes.
+	 */
+	mutex_lock(&sb_dqopt(sb)->dqonoff_mutex);
+	for (cnt = 0; cnt < MAXQUOTAS; cnt++) {
+		if (type != -1 && cnt != type)
+			continue;
+		if (!sb_has_quota_active(sb, cnt))
+			continue;
+		mutex_lock_nested(&sb_dqopt(sb)->files[cnt]->i_mutex,
+				  I_MUTEX_QUOTA);
+		truncate_inode_pages(&sb_dqopt(sb)->files[cnt]->i_data, 0);
+		mutex_unlock(&sb_dqopt(sb)->files[cnt]->i_mutex);
+	}
+	mutex_unlock(&sb_dqopt(sb)->dqonoff_mutex);
+
 	return 0;
 }
 EXPORT_SYMBOL(vfs_quota_sync);