From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 52B0F448B99; Thu, 30 Jul 2026 17:59:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785434395; cv=none; b=joAJH7b5wgBos8PhPIKpdEyXt1Pc5oDd2vvsVbWJtRurv+nOnIkldpcS39bYzoaVQoBvJgw9C0I8KWcsFiVW5IGk2hzw/MZWR+7Jl6qdJovo2VloJJ/Auj/E6CrmBLbimjUDOOrW9YY6sAjHi+WPYkJOTsMSz1ft8ocQMxtW4lw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785434395; c=relaxed/simple; bh=OOgJ48JRxMdktncZONk8v+GiWtu/r5iK09h3e4g98SM=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=ZGh+8lUinsPa1G86C01dhcxsHERX1SIeV5uAk1EJIKDZzaejWorLMfA60f8tyiJK/rpTuI4QyYserljveU8kKfjIxB20ecnT8PwAGYtw75EhDaDmj9aJASD61G/QEhkOu6s9A3Pvsze7u/HwvTq+w64bbwdGbeagkEMLIlACyb8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=UshECIue; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="UshECIue" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5ACE51F000E9; Thu, 30 Jul 2026 17:59:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1785434393; bh=YZrCgdyXy0gel21g6+l3wAl91/gQK/6PxbGO/1UYQNI=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=UshECIueGJWRMP+SZQFVcW0KEfohxvJ8oK09e7hIWV+2DIe4dmG2UVxZALb6bPcT5 0U1hW+6R6guYUtI0aiN5wXC8mVznh7PRZkBVADUy807+Y/d5CepvjAv+YyE6B+dn2q 66ns3oQYRRGuNTh6RCVt577rqxUpB9uVhkPVSXhs= Date: Thu, 30 Jul 2026 10:59:52 -0700 From: Andrew Morton To: Yosry Ahmed Cc: Hao Jia , tj@kernel.org, hannes@cmpxchg.org, shakeel.butt@linux.dev, mhocko@kernel.org, mkoutny@suse.com, nphamcs@gmail.com, chengming.zhou@linux.dev, muchun.song@linux.dev, roman.gushchin@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, Hao Jia , stable@vger.kernel.org Subject: Re: [PATCH v3 1/2] mm/zswap: Fix global shrinker when memory cgroup is disabled Message-Id: <20260730105952.7878a648c43c32b5e649d96d@linux-foundation.org> In-Reply-To: References: <20260729084206.77793-1-jiahao.kernel@gmail.com> <20260729084206.77793-2-jiahao.kernel@gmail.com> <20260729155858.c7aabff48166a9bca4d68ac3@linux-foundation.org> <20260729181756.a37e0cc7ea3f6013959d1d25@linux-foundation.org> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Thu, 30 Jul 2026 09:52:38 -0700 Yosry Ahmed wrote: > > > > > > > > How does this affect users? What behavior do they observe when it > > > > occurs? > > > > > > I think the first paragraph sums it up pretty well, especially the > > > last sentence "hotter pages with higher fault latency". > > > > How do users observe that? > > > > See, what I'm looking for here is an explanation for why we're > > proposing a backport. How are our users harmed by the current code and > > how does this change benefit them? > > It's a potential performance regression when using zswap with memcg > disabled. Sorry I just realized you were looking for a high level > description not detailed symptoms :) Are we able to guess how significant this is? It should have significant impact to justify a backport. Sorry to push - I'm forever trying to train people to describe the userspace-visible effects so we can make these backporting decisions! And to justify those decisions to -stable maintainers And so that someone who is experiencing a slowdown in some private kernel branch can look at the changelog and decide whether this might fix it for them.