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Tue, 08 Apr 2025 12:55:37 -0700 (PDT) Date: Tue, 8 Apr 2025 15:55:33 -0400 From: Johannes Weiner To: Igor Belousov Cc: Nhat Pham , vitaly.wool@konsulko.se, linux-mm@kvack.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, Shakeel Butt , Yosry Ahmed Subject: Re: [PATCH v2] mm: add zblock allocator Message-ID: <20250408195533.GA99052@cmpxchg.org> References: <1743810988579.7.125720@webmail-backend-production-7b88b644bb-5mmj8> <0dbbbe9d17ed489d4a7dbe12026fc6fd@beldev.am> <3f013184c80e254585b56c5f16b7e778@beldev.am> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3f013184c80e254585b56c5f16b7e778@beldev.am> On Tue, Apr 08, 2025 at 01:20:11PM +0400, Igor Belousov wrote: > >> >> Now what's funny is that when I tried to compare how 32 threaded build > >> >> would behave on a 8-core VM I couldn't do it because it OOMs with > >> >> zsmalloc as zswap backend. With zblock it doesn't, though, and the > >> >> results are: > >> >> real 12m14.012s > >> >> user 39m37.777s > >> >> sys 14m6.923s > >> >> Zswap: 440148 kB > >> >> Zswapped: 924452 kB > >> >> zswpin 594812 > >> >> zswpout 2802454 > >> >> zswpwb 10878 > >> > >> It's LZ4 for all the test runs. > > > > Can you try zstd and let me know how it goes :) > > Sure. zstd/8 cores/make -j32: > > zsmalloc: > real 7m36.413s > user 38m0.481s > sys 7m19.108s > Zswap: 211028 kB > Zswapped: 925904 kB > zswpin 397851 > zswpout 1625707 > zswpwb 5126 > > zblock: > real 7m55.009s > user 39m23.147s > sys 7m44.004s > Zswap: 253068 kB > Zswapped: 919956 kB > zswpin 456843 > zswpout 2058963 > zswpwb 3921 So zstd results in nearly double the compression ratio, which in turn cuts total execution time *almost in half*. The numbers speak for themselves. Compression efficiency >>> allocator speed, because compression efficiency ultimately drives the continuous *rate* at which allocations need to occur. You're trying to optimize a constant coefficient at the expense of a higher-order one, which is a losing proposition. This is a general NAK from me on any new allocators that cannot match or outdo zsmalloc storage density in common scenarios. I'm sorry, but I really don't see any reason to do this. We also should probably make zstd the zswap default.