On 1/28/25 00:58, 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> Seems weird not to Cc the folks listed in MAINTAINERS for ZBUD? Unless their addresses are known to bounce? And ZRAM maintainers should also be Ccd?
