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. Thanks. -- tejun
