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From: Roman Gushchin To: Michal Hocko Cc: Shakeel Butt , Andrew Morton , Johannes Weiner , Muchun Song , Hugh Dickins , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-doc@vger.kernel.org, Meta kernel team Subject: Re: [RFC PATCH 1/3] memcg-v1: fully deprecate move_charge_at_immigrate Message-ID: References: <20241024065712.1274481-1-shakeel.butt@linux.dev> <20241024065712.1274481-2-shakeel.butt@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 0972A140024 X-Stat-Signature: jtccapfoddboub35o6dkwsc1gjjma4qs X-Rspam-User: X-HE-Tag: 1729788699-240549 X-HE-Meta: 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 onxbz52s dE+nx3ohu+6PdnirbKvDoU8rgi8RjE7ppkbNAcnDFQ1DA+F4Ooa040boWuP8cuxLYn/0XicPaR+EAnkBySe2DOkImDlGmSMT08H79enkEBnjHL85uDlWTVkWvX35ZmkrNDinkYmsi1ydIBo3lAdczYfQMvxHBr6b1haANDqBPkx4HQGIrmKeS/NAY/MVlCzN0FUI2fMbHBRw7tjzoUP3paius9RlSefDvW9IKvwd5AItr712AhI6Nwyheryzo9edrRkXa+9riFqavpp3rgFNCmAE8bumZ8Qs/VNYc X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Oct 24, 2024 at 11:14:01AM +0200, Michal Hocko wrote: > On Wed 23-10-24 23:57:10, Shakeel Butt wrote: > > Proceed with the complete deprecation of memcg v1's charge moving > > feature. The deprecation warning has been in the kernel for almost two > > years and has been ported to all stable kernel since. Now is the time to > > fully deprecate this feature. > > > > Signed-off-by: Shakeel Butt > > I fine with this move, just one detail we might need to consider > [...] > > @@ -606,17 +606,7 @@ static int mem_cgroup_move_charge_write(struct cgroup_subsys_state *css, > > "Please report your usecase to linux-mm@kvack.org if you " > > "depend on this functionality.\n"); > > > > - if (val & ~MOVE_MASK) > > - return -EINVAL; > > - > > - /* > > - * No kind of locking is needed in here, because ->can_attach() will > > - * check this value once in the beginning of the process, and then carry > > - * on with stale data. This means that changes to this value will only > > - * affect task migrations starting after the change. > > - */ > > - memcg->move_charge_at_immigrate = val; > > - return 0; > > + return -EINVAL; > > Would it make more sense to -EINVAL only if val != 0? The reason being > that some userspace might be just writing 0 here for whatever reason and > see the failure unexpected. I think it's a good idea. Thanks!