On Wed, Jan 29, 2025 at 06:06:32PM +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. > > Remove zbud after z3fold's removal, leaving zsmalloc as the one and only > zpool allocator. Leave the removal of the zpool API (and its associated > config options) to a followup cleanup after no more allocators show up. > > Deprecating zbud for a few cycles before removing it was initially > proposed [2], like z3fold was marked as deprecated for 2 cycles [3]. > However, Johannes rightfully pointed out that the 2 cycles is too short > for most downstream consumers, and z3fold was deprecated first only as a > courtesy anyway. > > [1]https://lore.kernel.org/lkml/CAJD7tkbRF6od-2x_L8-A1QL3=2Ww13sCj4S3i4bNndqF+3+_Vg@xxxxxxxxxxxxxx/ > [2]https://lore.kernel.org/lkml/Z5gdnSX5Lv-nfjQL@xxxxxxxxxx/ > [3]https://lore.kernel.org/lkml/20240904233343.933462-1-yosryahmed@xxxxxxxxxx/ > > Signed-off-by: Yosry Ahmed <yosry.ahmed@xxxxxxxxx> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
