From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lgeamrelo12.lge.com (lgeamrelo12.lge.com [156.147.23.52]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1818D379C2F for ; Tue, 23 Jun 2026 01:29:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=156.147.23.52 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782178197; cv=none; b=I9pm+MZpVOLQnqYvOMv1QWj/qodWw4BBkozjL5dUjt33xyP8jvBIsvmEFMnw49kKKLcsMWumu0loQ/QpWwx1WDqw3/cxZ7LUzm7NdL6ybzCXNrYz5Z/KbwhGz7ggSQcLguYDpNB+rpC2YO7VnbEXggJW/pGQnsJCY0LXRh5RXd8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782178197; c=relaxed/simple; bh=g7AnO37BBHfkf4A/3eaC+5htqNFLtJU5lOEv/R0NBFc=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ADLchOb5ZbjBYe8RNC2g+bZmhouBwvPgIrlylEUji3JfDRiTwzai6ZGLx5oeDC2yPmrvQTrQi2RPphmMd+xgCqvn21C8r7+YhQn4u97N3e/yQQkUjCuUBAbM+XPlqbWWS7kg6k88SmKYcM9bg5ZlLIbHDuDRd0caGhjiV3SxoNY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=lge.com; spf=pass smtp.mailfrom=lge.com; arc=none smtp.client-ip=156.147.23.52 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=lge.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=lge.com Received: from unknown (HELO lgeamrelo02.lge.com) (156.147.1.126) by 156.147.23.52 with ESMTP; 23 Jun 2026 10:29:52 +0900 X-Original-SENDERIP: 156.147.1.126 X-Original-MAILFROM: youngjun.park@lge.com Received: from unknown (HELO yjaykim-PowerEdge-T330) (10.177.112.154) by 156.147.1.126 with ESMTP; 23 Jun 2026 10:29:52 +0900 X-Original-SENDERIP: 10.177.112.154 X-Original-MAILFROM: youngjun.park@lge.com Date: Tue, 23 Jun 2026 10:29:52 +0900 From: Youngjun Park To: Yosry Ahmed Cc: Youngjun Park , 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, shakeel.butt@linux.dev, muchun.song@linux.dev, shikemeng@huaweicloud.com, nphamcs@gmail.com, baoquan.he@linux.dev, baohua@kernel.org, gunho.lee@lge.com, taejoon.song@lge.com, hyungjun.cho@lge.com, mkoutny@suse.com, baver.bae@lge.com, matia.kim@lge.com Subject: Re: [PATCH v9 0/6] mm/swap, memcg: Introduce swap tiers for cgroup based swap control Message-ID: References: <20260620181635.299364-1-youngjun.park@lge.com> 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 Mon, Jun 22, 2026 at 02:23:40PM -0700, Yosry Ahmed wrote: > On Sat, Jun 20, 2026 at 11:16 AM Youngjun Park wrote: > > > > This is the v9 series of the swap tier patchset. > > > > The main change in this version is the addition of selftests for the tier > > interfaces, requested by Nhat; see the changelog below for the other changes. > > I designed the test cases and wrote the selftests with some AI assistance. > > > > 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]: > > Tiering applies only to the vswap + zswap combo. Zswap itself will > > not be tiered, as the current architecture requires a physical device > > for zswap allocation. > > I thought we agreed that zswap should be a tier, so that proactive > zswap writeback can be implemented as proactive swap demotion? > > The only restriction we talked about is that zswap cannot be the only > allowed tier as long as vswap isn't supported. We can lift the > restriction when vswap support is added. Okay, I misunderstood that part. Thanks for the clarification. To summarize our agreement. zswap can be the first tier regardless of vswap support. - With vswap: zswap can be the only allowed tier, as it can operate independently. - Without vswap: zswap cannot be the only allowed tier, as it cannot operate without a physical backing device. I will proceed with this understanding. Youngjun Park