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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 v2 2/2] mm/vmpressure: split v1 userspace eventfd code into vmpressure-v1.c Message-ID: References: <20260629130042.2649505-1-usama.arif@linux.dev> <20260629130042.2649505-3-usama.arif@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: <20260629130042.2649505-3-usama.arif@linux.dev> X-Migadu-Flow: FLOW_OUT On Mon, Jun 29, 2026 at 05:59:37AM -0700, Usama Arif wrote: > Clean up mm/vmpressure.c by separating the cgroup v1 userspace eventfd > interface from the shared and v2 in-kernel code. > > Currently, almost half of mm/vmpressure.c exists to serve tree=true: > struct vmpressure_event, the events list and its mutex, the work_struct > and vmpressure_work_fn that drains tree_scanned/tree_reclaimed, the > parent walk, vmpressure_event(), vmpressure_register_event(), > vmpressure_unregister_event(), and vmpressure_prio() (which always > calls vmpressure() with tree=true). > > Move it all into a new mm/vmpressure-v1.c built only when > CONFIG_MEMCG_V1=y (following the existing memcontrol-v1.o pattern). > > vmpressure.c keeps the shared bits (constants, vmpressure_calc_level, > the runtime hierarchy check, the tree=false body, init/cleanup > plumbing) and calls into three small v1 hooks for the tree=true > accumulator and the v1 portions of init/cleanup. The hooks have > static-inline no-op stubs in include/linux/vmpressure.h for the > !MEMCG_V1 case, so callers don't need ifdefs. vmpressure_prio() gets > the same treatment, which means vmscan.c's call site disappears at > compile time on v2-only kernels. > > The only #ifdef CONFIG_MEMCG_V1 in source remains around the v1-only > fields inside struct vmpressure itself. > > Memory savings on CONFIG_MEMCG_V1=n (measured with pahole): > > struct vmpressure : 112B -> 24B > struct mem_cgroup : 1664B -> 1536B > > 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. > > Signed-off-by: Usama Arif Acked-by: Shakeel Butt