January 28, 2025 at 2:14 AM, "Johannes Weiner" <hannes@xxxxxxxxxxx> wrote: > > On Mon, Jan 27, 2025 at 11:58:21PM +0000, Yosry Ahmed wrote: > > > > > The zbud compressed pages allocator is rarely used, most users use > > > > zsmalloc. zbud consumes much more memory (only stores 1 or 2 compressed > > > > pages per physical page). The only advantage of zbud is a marginal > > > > performance improvement that by no means justify the memory overhead. > > > > > > > > Historically, zsmalloc had significantly worse latency than zbud and > > > > z3fold but offered better memory savings. This is no longer the case as > > > > shown by a simple recent analysis [1]. In a kernel build test on tmpfs > > > > in a limited cgroup, zbud 2-3% less time than zsmalloc, but at the cost > > > > of using ~32% more memory (1.5G vs 1.13G). The tradeoff does not make > > > > sense for zbud in any practical scenario. > > > > > > > > The only alleged advantage of zbud is not having the dependency on > > > > CONFIG_MMU, but CONFIG_SWAP already depends on CONFIG_MMU anyway, and > > > > zbud is only used by zswap. > > > > > > > > Following in the footsteps of [2], which deprecated z3fold, deprecated > > > > zbud as planned and remove it in a few cycles if no objections are > > > > raised from active users. > > > > > > > > Rename the user-visible config options so that users with CONFIG_ZBUD=y > > > > get a new prompt with explanation during make oldconfig. Also, remove > > > > CONFIG_ZBUD from defconfig. > > > > > > > > [1]https://lore.kernel.org/lkml/CAJD7tkbRF6od-2x_L8-A1QL3=2Ww13sCj4S3i4bNndqF+3+_Vg@xxxxxxxxxxxxxx/ > > > > [2]https://lore.kernel.org/lkml/20240904233343.933462-1-yosryahmed@xxxxxxxxxx/ > > > > > > > > Signed-off-by: Yosry Ahmed <yosry.ahmed@xxxxxxxxx> > > > > Can we just drop it right away? > > The two cycles for z3fold were basically in the "not worth bothering" > > category, since very few downstream production systems rebase that > > frequently. > > zsmalloc has been in use on everything from mobile devices to large > > servers for years. It's been the default since 6.6 (Oct '23) for > > zswap, and the only option for zram from the start. I certainly do not object, if no one else objects I can do that. We can leave the zpool code around for a bit in case a new allocator shows up tho, just as due diligence.
