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

[Nick Piggin]

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?

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/