Re: [PATCH 04/19] fs: Implement lazy LRU updates for inodes.

Nick Piggin
2010-10-16T17:34:29Z

On Sun, Oct 17, 2010 at 04:29:24AM +1100, Nick Piggin wrote:
> On Sat, Oct 16, 2010 at 12:59:30PM -0400, Christoph Hellwig wrote:
> > I don't think the pointer check will work either. By the time we retake
> > the lru lock the inode might already have been reaped through a call
> > to invalidate_inodes. There's no way we can do anything with it after
>
> I don't think you're right. If we re take inode_lock, ensure it is on
> the LRU, and call the can_unuse checks, there is no more problem than
> the regular loop taking items from the LRU, AFAIKS.
>
> > iput. What we could do is using variant of can_unuse to decide to move
> > the inode to the front of the lru before doing the iput. That way
> > we'll get to it next after retaking the lru lock if it's still there.
>
> This might actually be the better approach anyway (even for upstream)
> -- it means we don't have to worry about the "check head element"
> heuristic of the LRU check which could get false negatives if there is
> a lot of concurrency on the LRU.

Oh hmm, but then you do have the double lock of the LRU lock.

if (can_unuse_after_iput(inode)) {
spin_lock(&inode_lock);
list_move(inode, list tail)
spin_unlock(&inode_lock);
}
iput(inode);
spin_lock(&inode_lock);

Is that worth it?