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Commit 941d2380 authored by Jan Kara's avatar Jan Kara Committed by Linus Torvalds
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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: default avatarJan Kara <jack@suse.cz>
Cc: Nick <gentuu@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus 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 @@ static void add_dquot_ref(struct super_block *sb, int type) 
		__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) */