Commit 941d2380 authored Feb 06, 2008 by Jan Kara Committed by Linus Torvalds Feb 06, 2008

quota: improve inode list scanning in add_dquot_ref()



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 <gentuu@gmail.com> for analyzing the problem and
testing the fix.

[akpm@linux-foundation.org: iput(NULL) is legal]
Signed-off-by: Jan Kara <jack@suse.cz>
Cc: Nick <gentuu@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent bed9759b

fs/dquot.c

+10 −5

Original line number	Diff line number	Diff line
		@@ -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 +710,18 @@ restart:
		__iget(inode);
		spin_unlock(&inode_lock);

		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);
		iput(old_inode);
		}

		/* Return 0 if dqput() won't block (note that 1 doesn't necessarily mean blocking) */

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