Messages in this thread | | | Date | Sun, 17 Oct 2010 13:09:51 +1100 | From | Nick Piggin <> | Subject | Re: [PATCH 04/19] fs: Implement lazy LRU updates for inodes. |
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On Sat, Oct 16, 2010 at 08:47:10PM -0400, Christoph Hellwig wrote: > On Sun, Oct 17, 2010 at 04:29:24AM +1100, Nick Piggin 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. > > As long as we have the global inode lock it should indeed be safe. > But once we have a separate lru lock (global or per-zone, with or > without i_lock during the addition) there is nothing preventing the > inode from getting reused and re-added to the lru in the meantime. > Sure this is an extremly unlikely case, but there is no locking to > prevent it once inode_lock is gone.
No. There is nothing preventing that exact reuse from happening in mainline _today_ either, because the inode_lock is dropped there too.
The point is that it is a heuristic that works (apparently) most of the time but if it gets it wrong then it's not a big deal, it's only the LRU position anyway. It would work exactly the same with separate global or per-zone lru locks.
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