On Sat, 7 Jun 2014 07:09:04 -0700 Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > On Fri, Jun 06, 2014 at 09:07:06AM -0400, Jeff Layton wrote: > > state_lock is a heavily contended global lock. We don't want to grab > > that while simultaneously holding the inode->i_lock. Avoid doing that in > > the delegation break callback by ensuring that we add/remove the > > dl_perfile under a new per-nfs4_file fi_lock, and hold that while walking > > the fi_delegations list. > > > > We still do need to queue the delegations to the global del_recall_lru > > list. Do that in the rpc_prepare op for the delegation recall RPC. It's > > possible though that the allocation of the rpc_task will fail, which > > would cause the delegation to be leaked. > > > > If that occurs rpc_release is still called, so we also do it there if > > the rpc_task failed to run. This brings up another dilemma -- how do > > we know whether it got queued in rpc_prepare or not? > > > > In order to determine that, we set the dl_time to 0 in the delegation > > break callback from the VFS and only set it when we queue it to the > > list. If it's still zero by the time we get to rpc_release, then we know > > that it never got queued and we can do it then. > > Compared to this version I have to say the original one that I objected > to looks like the lesser evil. I'll take another deeper look at it. > Well, I think using the fp->fi_lock instead of the i_lock here is reasonable. We at least avoid taking the state_lock (which is likely to be much more contended) within the i_lock. The thing that makes this patch nasty is all of the shenanigans to queue the delegation to the global list from within rpc_prepare or rpc_release. Personally, I think it'd be cleaner to add some sort of cb_prepare operation to the generic callback framework you're building to handle that, but let me know what you thing. -- Jeff Layton <jlayton@xxxxxxxxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
