On Sat, Aug 03, 2019 at 08:53:49AM -0700, Tejun Heo wrote: > Hey, Matthew. > > On Sat, Aug 03, 2019 at 08:39:08AM -0700, Matthew Wilcox wrote: > > On Sat, Aug 03, 2019 at 07:01:53AM -0700, Tejun Heo wrote: > > > There currently is no way to universally identify and lookup a bdi > > > without holding a reference and pointer to it. This patch adds an > > > non-recycling bdi->id and implements bdi_get_by_id() which looks up > > > bdis by their ids. This will be used by memcg foreign inode flushing. > > > > > > I left bdi_list alone for simplicity and because while rb_tree does > > > support rcu assignment it doesn't seem to guarantee lossless walk when > > > walk is racing aginst tree rebalance operations. > > > > This would seem like the perfect use for an allocating xarray. That > > does guarantee lossless walk under the RCU lock. You could get rid of the > > bdi_list too. > > It definitely came to mind but there's a bunch of downsides to > recycling IDs or using radix tree for non-compacting allocations. Ah, I wasn't sure what would happen if you recycled an ID. I agree, the radix tree is pretty horrid for monotonically increasing IDs. I'm still working on the maple tree to replace it, but that's going slower than I would like, so I can't in good conscience ask you to wait for it to be ready.
