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From: Shakeel Butt To: Usama Arif Cc: Andrew Morton , david@kernel.org, linux-mm@kvack.org, hannes@cmpxchg.org, tj@kernel.org, mkoutny@suse.com, roman.gushchin@linux.dev, liam@infradead.org, linux-kernel@vger.kernel.org, ljs@kernel.org, mhocko@suse.com, rppt@kernel.org, surenb@google.com, vbabka@kernel.org, kernel-team@meta.com Subject: Re: [PATCH 0/2] mm/vmpressure: reduce CPU, memory and code overhead on cgroup v2 Message-ID: References: <20260606114158.3126210-1-usama.arif@linux.dev> <750406a5-1819-4ca6-81d8-5a1d82e0644b@linux.dev> <744aae62-ad99-4534-906e-92ddad978ee1@linux.dev> 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=us-ascii Content-Disposition: inline In-Reply-To: <744aae62-ad99-4534-906e-92ddad978ee1@linux.dev> X-Migadu-Flow: FLOW_OUT On Mon, Jun 08, 2026 at 10:19:36PM +0100, Usama Arif wrote: > > > On 08/06/2026 20:56, Shakeel Butt wrote: > > On Mon, Jun 08, 2026 at 07:49:45PM +0100, Usama Arif wrote: > >> > >> > >>> > >>> For this, I am wondering if we should just go ahead and work towards making > >>> vmpressure memcg-v1 only unless we foresee a lot of or complex work is needed > >>> for that and only then patch 2 makes sense. > >>> > >> > >> I think there might be a transition needed? Because vmpressure and PSI > >> do not work out to be the same and people might notice a regression with > >> increased memory usage or a hit in networking performance and might want to > >> opt out? A solution might be to switch socket pressure to PSI while > >> keeping vmpressure around gated by a defconfig. And then in a few releases > >> remove it completely for cgroup v2 if no one complaints. If we go down that > >> path, we would need patch 2 for the medium term. > > > > Yeah the reasoning that PSI is not an exact replacement for vmpressure makes > > sense and it will take couple of iterations to transition v2 (networking) away > > from vmpressure. Can you please update your commit message with this and about > > the midterm or transition plan. > > > > I assume eventually we will just have vmpressure-v1.c file which will be behind > > MEMCG_V1 flag, correct? > > Yes. > > How about something like below in the commit message? : > > This split is the first step toward eventually making vmpressure > CONFIG_MEMCG_V1 only. The v2 in-kernel socket pressure path > (tree=false) cannot be removed today immediately: PSI is not an > exact replacement for vmpressure, and switching networking socket-buffer > back-off to PSI may regress networking performance or increase memory pressure > in workloads that today rely on vmpressure's hysteresis. The medium-term plan is > to introduce a PSI-based socket-pressure path, keep vmpressure available for > v2 behind a defconfig as an opt-out for several releases, and only then > drop the tree=false path entirely, at which point everything that > remains in mm/vmpressure-v1.c is the whole subsystem. > This looks good to me.