Hi,
attached patch makes add_dquot_ref() quite faster if used on a life
filesystem. It has survived some testing on my machine but there could be
some subtle races I've missed so please leave it in -mm for a while (not
that I'd think that people use quotas with -mm kernels but at least it
should go into vanilla in -rc1...). Thanks.
Honza
---
We restarted scan of sb->s_inodes list whenever we had to drop inode_lock in
add_dquot_ref(). This leads to overall quadratic running time and thus
add_dquot_ref() can take several minutes when called on a life filesystem. We
fix the problem by using the fact that inode cannot be removed from s_inodes
list while we hold a reference to it and thus we can safely restart the scan if
we don't drop the reference. Here we use the fact that inodes freshly added to
s_inodes list are already guaranteed to have quotas properly initialized and
the ordering of inodes on s_inodes list does not change so we cannot skip any
inode. Thanks goes to Nick <[email protected]> for analyzing the problem and
testing the fix.
Signed-off-by: Jan Kara <[email protected]>
CC: Nick <[email protected]>
diff --git a/fs/dquot.c b/fs/dquot.c
index 2809768..ecea4be 100644
--- a/fs/dquot.c
+++ b/fs/dquot.c
@@ -696,9 +696,8 @@ static int dqinit_needed(struct inode *inode, int type)
/* This routine is guarded by dqonoff_mutex mutex */
static void add_dquot_ref(struct super_block *sb, int type)
{
- struct inode *inode;
+ struct inode *inode, *old_inode = NULL;
-restart:
spin_lock(&inode_lock);
list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
if (!atomic_read(&inode->i_writecount))
@@ -711,12 +710,20 @@ restart:
__iget(inode);
spin_unlock(&inode_lock);
+ if (old_inode)
+ iput(old_inode);
sb->dq_op->initialize(inode, type);
- iput(inode);
- /* As we may have blocked we had better restart... */
- goto restart;
+ /* We hold a reference to 'inode' so it couldn't have been
+ * removed from s_inodes list while we dropped the inode_lock.
+ * We cannot iput the inode now as we can be holding the last
+ * reference and we cannot iput it under inode_lock. So we
+ * keep the reference and iput it later. */
+ old_inode = inode;
+ spin_lock(&inode_lock);
}
spin_unlock(&inode_lock);
+ if (old_inode)
+ iput(old_inode);
}
/* Return 0 if dqput() won't block (note that 1 doesn't necessarily mean blocking) */
--
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