On Fri, Mar 01, 2024 at 09:58:43PM +0000, David Laight wrote: > From: Chris Li > > Sent: 29 February 2024 08:46 > > > > Very deep RB tree requires rebalance at times. That > > contributes to the zswap fault latencies. Xarray does not > > need to perform tree rebalance. Replacing RB tree to xarray > > can have some small performance gain. > > > > One small difference is that xarray insert might fail with > > ENOMEM, while RB tree insert does not allocate additional > > memory. > > What is the difference in kernel memory use? > IIRC someone pointed out (in the rosebush thread) that xarray > uses a lot of kernel memory if the items are randomly distributed. I often thought it would be useful if there is an API for the xarray to report how much memory it's using. For zswap, we could plumb this to a debugfs interface or so to measure the tree usage and compare to the rbtree. The cost is fixed with the rbtree IIUC, 3 words per zswap entry.
