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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> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 7F53E18001C X-Stat-Signature: j1h5t97usboeesw4g5g565hdctmqawk7 X-HE-Tag: 1757430210-346090 X-HE-Meta: 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 8ATlCZ8W 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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.