On Tue, 11 Dec 2007 14:43:19 +0100
Jan Kara <[email protected]> wrote:
> 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);
> }
>
iput(NULL) is legal. In the great majority of cases old_inode!=NULL so I
think we should use that feature here?
--- a/fs/dquot.c~quota-improve-inode-list-scanning-in-add_dquot_ref-fix
+++ a/fs/dquot.c
@@ -710,8 +710,7 @@ static void add_dquot_ref(struct super_b
__iget(inode);
spin_unlock(&inode_lock);
- if (old_inode)
- iput(old_inode);
+ iput(old_inode);
sb->dq_op->initialize(inode, type);
/* We hold a reference to 'inode' so it couldn't have been
* removed from s_inodes list while we dropped the inode_lock.
@@ -722,8 +721,7 @@ static void add_dquot_ref(struct super_b
spin_lock(&inode_lock);
}
spin_unlock(&inode_lock);
- if (old_inode)
- iput(old_inode);
+ iput(old_inode);
}
/* Return 0 if dqput() won't block (note that 1 doesn't necessarily mean blocking) */
_
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