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From: Shakeel Butt To: Roman Gushchin Cc: Michal Hocko , 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-Stat-Signature: u1336w883i9jknftgtz4ojfsof87un9j X-Rspamd-Queue-Id: BE2BC80002 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1729790191-981189 X-HE-Meta: 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 JLaSLhO5 HIz8aVfTUKaMlUgApPCqfGQm0RtPCzr8JxZ3tkJnw21hKVXF4NNHBnYckpVaPB+o4WAqC4l5G0ohPgrduUp6CqRCYgB0OI2etRDIOqtoJvYrfCM4tgqMsn7ECLYROu0+yttOSeSDT6iEbmEQP35NETbu0sJoA5REOLkNv2/a9S/GRdTUybBm8DeTtUVuzQuitaaIKNYCsX4s6YZCzkUgFK0TupuYzAjmG2JtzCkhXVU3E5i+NhQk+nA/7Vt4cZeKduuoc 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 04:51:46PM GMT, Roman Gushchin wrote: > 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! Thanks Michal and Roman for the review and I will make this change in the next version.