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Sun, 04 Oct 2026 11:14:06 -0700 (PDT) Date: Mon, 5 Oct 2026 03:13:58 +0900 From: Youngjun Park To: Matthias Goergens Cc: Kairui Song , Andrew Morton , Chris Li , Baoquan He , Johannes Weiner , David Hildenbrand , Michal Hocko , Shakeel Butt , Kemeng Shi , Nhat Pham , Yosry Ahmed , Barry Song , linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-api@vger.kernel.org, Alejandro Colomar , linux-man@vger.kernel.org, Karel Zak , util-linux@vger.kernel.org, Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , Tvrtko Ursulin , David Airlie , Simona Vetter , intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, "Rafael J . Wysocki" , Pavel Machek , Catalin Marinas , Will Deacon , linux-pm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Shuah Khan , linux-kselftest@vger.kernel.org, Kairui Song Subject: Re: [RFC PATCH v2 0/4] mm/swap: reserve swap areas for deliberate offload Message-ID: References: <20260926045517.3458413-1-matthias.goergens@gmail.com> <20260928151944.2686626-1-matthias.goergens@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260928151944.2686626-1-matthias.goergens@gmail.com> X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: C170040002 X-Stat-Signature: 1nkkdju7ck5d3tbh6eizmceujrcd5r9u X-Rspam-User: X-HE-Tag: 1791137649-924240 X-HE-Meta: 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 iSFXB/nF 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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 2026-09-28 23:19, Matthias Goergens wrote: Hi Matthias ! > > Just like we already have a "swappiness=" parameter in the reclaim > > interface, perhaps adding a "swap.tier=" would be better and much > > cleaner to achieve the same goal? Based on Youngjun's work here: > > https://lore.kernel.org/all/20260916183437.2946306-1-youngjun.park@lge.com/ > > Thanks, I think that's the right base. I tried it: on top of > Youngjun's v11, a "swap.tier=" argument to memory.reclaim is about 40 > lines. In a VM with zram at a higher priority than a disk swap > device, and a cgroup whose tier mask allowed only the disk, ordinary > reclaim in that cgroup stayed on the disk, while memory.reclaim with > "swap.tier=" pointing at zram went to zram only. There is an earlier attempt that may be worth a look. https://lore.kernel.org/all/20260618044857.69439-1-jiahao.kernel@gmail.com/ If you go this way, the discussion in that thread worth refering too. > What it doesn't cover yet is reclaim outside any configured cgroup: > under global pressure, a cgroup nobody configured still reached the Right, so for now every cgroup has to be set to exclude zram, unless another idea or more code covers it. > zram tier. So for v3 I'd like to add a system-wide limit on which > tiers pressure reclaim may use, on top of the per-cgroup settings. > I'll wait for Youngjun's v12 and build on that. I have looked through the whole series, and I will keep this use case in mind while working on v12. :) Also, to share what I had in mind, I was planning a sysfs interface for each swap tier, /sys/kernel/mm/swap/tiers/ (exact naming TBD). Maybe the system-wide limit could be handled there as one of its use cases? Let's discuss it in more detail after v12. Thanks, Youngjun