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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) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: A7F7E140005 X-Rspam-User: X-Stat-Signature: s5otewx8smat9pygap7kqwgqcp3nn1rf X-HE-Tag: 1785434395-325961 X-HE-Meta: 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 JxKHE95B icCsofVySvXGrbO1YmndKaOCiui7vpnkH+SNuAAAKuybeRjAi3HdpneXex05esZNPQkR9tj2olIgryF5owgtb8QvRsjkYhJDyOgeIoBk5smp7mcUHqIflUcZZIqaf4wGmjN3QopYjEoqGtdb3Zz53k2vcY8HTknkyj7T69OZ1W9flkBprT3SQ2grpmVN/bccgibkQS5nmX7HpGdj2LKxAp3xsLuOKuWuRyYGmq8dDc9NhW2ohfiB6B8kCvXFwjomeGlHxUrI4XiGiKFOpfz6oePbr3SIoJwyo8eKCnu3nn23OWWmCmNyT8jYocy58NdZ1s8JmwpiTZS8T5F7CnfOFqPoAg0McDMWRe2Gz Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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.