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From: Shakeel Butt To: Youngjun Park Cc: Yosry Ahmed , akpm@linux-foundation.org, chrisl@kernel.org, linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kasong@tencent.com, hannes@cmpxchg.org, mhocko@kernel.org, roman.gushchin@linux.dev, muchun.song@linux.dev, shikemeng@huaweicloud.com, baoquan.he@linux.dev, baohua@kernel.org, joshua.hahnjy@gmail.com, gunho.lee@lge.com, taejoon.song@lge.com, hyungjun.cho@lge.com, baver.bae@lge.com, her0gyugyu@gmail.com Subject: Re: [PATCH v10 0/6] mm/swap, memcg: Introduce swap tiers for cgroup based swap control Message-ID: References: <20260713025644.170839-1-youngjun.park@lge.com> Precedence: bulk X-Mailing-List: cgroups@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: X-Migadu-Flow: FLOW_OUT Hi Youngjun, Thanks for keep pushing this effort. On Tue, Jul 14, 2026 at 01:22:42AM +0900, Youngjun Park wrote: > On Mon, Jul 13, 2026 at 09:01:20AM -0700, Yosry Ahmed wrote: > > On Mon, Jul 13, 2026 at 8:57 AM Youngjun Park wrote: > > > > > > On Mon, Jul 13, 2026 at 08:50:36AM -0700, Yosry Ahmed wrote: > > > > On Sun, Jul 12, 2026 at 7:57 PM Youngjun Park wrote: > > > > > > > > > > This is the v10 series of the swap tier patchset. > > > > > > > > > > v10 folds in the Sashiko review fixes for the selftests added in v9 and > > > > > rebases onto the current mm-new. There are no functional changes to the > > > > > core swap or memcg code since v9; see the changelog for details. > > > > > > > > > > For context, the bulk of the series is unchanged since v8, with great thanks > > > > > to Shakeel Butt and Yosry for the reviews and discussions [1] that shaped it. > > > > > The main change in v8 was the interface change to use memory.swap.tiers.max > > > > > with '0' (disable) and 'max' (enable) values. This mechanism was suggested > > > > > by Shakeel and Yosry. > > > > > > > > > > This change allows for future extensions to control swap between tiers and > > > > > aligns better with existing memcg interfaces. It is confined to patch #3's > > > > > user-facing interface; internally, patch #3 still uses the existing mask > > > > > processing method, which is implementation-efficient. > > > > > > > > > > We also discussed tier extensions. Thanks to Yosry, Nhat and Shakeel for their > > > > > valuable feedback. > > > > > > > > > > Here is a brief summary of our tentative conclusions. Please correct me > > > > > if anything is misrepresented (details in references): > > > > > > > > > > * Zswap tiering [2]: > > > > > Zswap can itself be a tier (typically the fastest one). But, until vswap lands, > > > > > zswap cannot be the only allowed tier, > > > > > since it still needs a physical device for allocation; > > > > > that restriction can be lifted once vswap is supported. > > > > > > > > Does this series support zswap being a tier? I cannot find any mention > > > > of zswap in the patches. > > > > > > Hello Yosry! > > > > > > This series does not cover zswap as a tier yet. > > > > > > My plan is to land the swap tier infrastructure together with the > > > first use case (cgroup-based swap control) first, and then follow > > > up with zswap tier support in a subsequent series, continuing the > > > discussions we've had above. > > > (I mentioned on cover letter, right above the overview section) > > > > > > Does that approach sound reasonable to you? > > > > How does swap tiering work with zswap in the current series? I assume > > zswap is just enabled for all devices in all tiers? > > Yes, that's correct. > > > I wonder if introducing zswap as a tier after the fact changes user-visible > > behavior. I guess if zswap will be introduced with a default "max" > > value it will more-or-less be the same behavior, > > Right, that's the plan. > > > but I would check all > > user-visible behaviors related to zswap (e.g. interaction with other > > zswap interfaces) to make sure nothing breaks or changes in a > > meaningful way when zswap is introduced as a tier later. > > Fair point. Let me review this more and get back to you! Please do report back what you find. Yosry, what is needed to enable zswap as a swap tier? What will be the minimum requirements for that? If that is not too much, we can make that part of this series. Shakeel