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Tue, 09 Sep 2025 08:03:27 -0700 (PDT) Date: Tue, 9 Sep 2025 16:03:26 +0100 From: Johannes Weiner To: Nhat Pham Cc: Yosry Ahmed , Andrew Morton , Chengming Zhou , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 0/3] mm: remove zpool Message-ID: <20250909150326.GC1474@cmpxchg.org> References: <20250829162212.208258-1-hannes@cmpxchg.org> <4vpqew3bfs74kesmgd6kaafgm6nr6zbtt2t3hl2khkc6ds4zep@hllgy77hdumf> 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=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Fri, Sep 05, 2025 at 02:35:12PM -0700, Nhat Pham wrote: > On Fri, Sep 5, 2025 at 12:45 PM Yosry Ahmed wrote: > > > > On Fri, Sep 05, 2025 at 10:52:18AM -0700, Nhat Pham wrote: > > > On Fri, Aug 29, 2025 at 9:22 AM Johannes Weiner wrote: > > > > > > > > zpool is an indirection layer for zswap to switch between multiple > > > > allocator backends at runtime. Since 6.15, zsmalloc is the only > > > > allocator left in-tree, so there is no point in keeping zpool around. > > > > > > > > > > Taking a step back, even if we do have needs for multiple allocators > > > for different setups, having it runtime-selectable makes no sense. > > > > Honestly I think we should take it a step further and make the > > compressor selection only at build/boot time and completely get rid of > > supporting having multiple pools. We'd create one pool at initilization > > and that would be it. > > > > I believe this will simplify things considerably, and I doubt changing > > the compressor at runtime has a valid use case beyond experimentation. > > You are completely right. > > And, even if there's a setup where we benefit from multiple > compressors, the current setup is definitely not it. How are we > realistically going to use these sysfs knobs? Change to one > compressor, then quickly change it back? How is this remotely useful? > > Let's remove it all. In the future, if we want to do multiple > compression tiers, or per-cgroup compression algorithm, we will need a > completely different architecture anyway. +1 Completely agreed, it's not worth all this fragile code in zswap.c. I'll send follow-up patches.