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Tue, 24 Mar 2026 10:23:34 -0700 (PDT) MIME-Version: 1.0 References: <20260320192735.748051-1-nphamcs@gmail.com> <20260324131931.4004123-1-safinaskar@gmail.com> In-Reply-To: <20260324131931.4004123-1-safinaskar@gmail.com> From: Nhat Pham Date: Tue, 24 Mar 2026 13:23:22 -0400 X-Gm-Features: AQROBzC3hVhU93LxfbLzywKCT0KcJoCMPUplZMLmSEgnO1rcgM2PnL8QUVFELHg Message-ID: Subject: Re: [PATCH v5 00/21] Virtual Swap Space To: Askar Safin Cc: Liam.Howlett@oracle.com, akpm@linux-foundation.org, apopple@nvidia.com, axelrasmussen@google.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, bhe@redhat.com, byungchul@sk.com, cgroups@vger.kernel.org, chengming.zhou@linux.dev, chrisl@kernel.org, corbet@lwn.net, david@kernel.org, dev.jain@arm.com, gourry@gourry.net, hannes@cmpxchg.org, hughd@google.com, jannh@google.com, joshua.hahnjy@gmail.com, kasong@tencent.com, kernel-team@meta.com, lance.yang@linux.dev, lenb@kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-pm@vger.kernel.org, lorenzo.stoakes@oracle.com, matthew.brost@intel.com, mhocko@suse.com, muchun.song@linux.dev, npache@redhat.com, pavel@kernel.org, peterx@redhat.com, peterz@infradead.org, pfalcato@suse.de, rafael@kernel.org, rakie.kim@sk.com, riel@surriel.com, roman.gushchin@linux.dev, rppt@kernel.org, ryan.roberts@arm.com, shakeel.butt@linux.dev, shikemeng@huaweicloud.com, surenb@google.com, tglx@kernel.org, vbabka@suse.cz, weixugc@google.com, ying.huang@linux.alibaba.com, yosry.ahmed@linux.dev, yuanchu@google.com, zhengqi.arch@bytedance.com, ziy@nvidia.com, Kairui Song , Matthew Wilcox Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 69EB21A0007 X-Stat-Signature: u97qw643a3spwu4sc3zd7du5dmpwn4yh X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1774373016-540537 X-HE-Meta: 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 qwCPU670 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Mar 24, 2026 at 9:19=E2=80=AFAM Askar Safin = wrote: > > Nhat Pham : > > We can even perform compressed writeback > > (i.e writing these pages without decompressing them) (see [12]). > > > [12]: https://lore.kernel.org/linux-mm/ZeZSDLWwDed0CgT3@casper.infradea= d.org/ > > This is supported in zram. The support was added here: > https://lore.kernel.org/all/20251201094754.4149975-1-senozhatsky@chromium= .org/ . > It is already in mainline. I'm aware of that work. It's an improvement, but my understanding is: 1. It only works for zram. 2. We still occupy the full PAGE_SIZE slot. 3. The writeback IO request is still of size PAGE_SIZE. So we're saving the CPU work for decompression, but not the rest of the potential benefits of compressed writeback. For zswap, decoupling zswap and disk swap is a pre-requisite (otherwise every zswap slot occupy a PAGE_SIZE slot in the swapfile anyway). Then, we have two alternatives. Either we implement a small-slot allocator for swapfile-infra, or we writeback a full backing page for compressed memory. The second option is a bit more straightforward, but then we lose relative age of these objects - a backing page might combine very recent compressed pages and very old compressed pages. These approaches have different performance tradeoffs and need to be evaluated. But anyway this is future work.