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From: Shakeel Butt To: Kuniyuki Iwashima Cc: Andrew Morton , Johannes Weiner , "David S. Miller" , Vladimir Davydov , Kuniyuki Iwashima , linux-mm@kvack.org, Neal Cardwell Subject: Re: [PATCH v2] memcg: Convert memcg->socket_pressure to u64. Message-ID: References: <20250717194645.1096500-1-kuniyu@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250717194645.1096500-1-kuniyu@google.com> X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: 6064F40013 X-Stat-Signature: cuzppbn39t1j6f66hwqdbrmzp44kkggm X-Rspam-User: X-Rspamd-Server: rspam11 X-HE-Tag: 1752782489-13827 X-HE-Meta: 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 WfNWoEpb KqzK6l89dd9MMyVcU8ILUSzF/xH+VJUSdY4SePQooUPd8QmO+hxj189CiQqFVTSScQgkQiNpmQPsN/A+s7teRehfDIjV9NoQkinDCo6mGEm0kUPvsN33LTQZ1y6vebk2mG9wCDqHQZ5YgOfgG85j6TnoFMNxKACUcPDi3hRUhmZ9gPG+wHn4DkFfvXQleIeZjh+zosrykF5EYgkT3iOSwXh1/8MT4DpT7qPnyDtxOtWxJKNMGH3T7t+Hl31qJhboKHvmHxHGfssTvcAKxDogeiuqQNnJa9gLQ6OcMX0ZrhMvYWH58jhuIuXHLiEFOJM+ogh9Zba4p6+sYt0vllqNHT5+Qr2jIyqOfoqcGbffyl4Fn5v573QoYcGtigYZo2Nk+F9TPz3ZzpDLY3LuKcPtDb+Vz6e/APt6/m+qi 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, Jul 17, 2025 at 07:46:43PM +0000, Kuniyuki Iwashima wrote: > memcg->socket_pressure is initialised with jiffies when the memcg > is created. > > Once vmpressure detects that the cgroup is under memory pressure, > the field is updated with jiffies + HZ to signal the fact to the > socket layer and suppress memory allocation for one second. > > Otherwise, the field is not updated. > > mem_cgroup_under_socket_pressure() uses time_before() to check if > jiffies is less than memcg->socket_pressure, and this has a bug on > 32-bit kernel. > > if (time_before(jiffies, memcg->socket_pressure)) > return true; > > As time_before() casts the final result to long, the acceptable delta > between two timestamps is 2 ^ (BITS_PER_LONG - 1). > > On 32-bit kernel with CONFIG_HZ=1000, this is about 24 days. > > >>> (2 ** 31) / 1000 / 60 / 60 / 24 > 24.855134814814818 > > Once 24 days have passed since the last update of socket_pressure, > mem_cgroup_under_socket_pressure() starts to lie until the next > 24 days pass. > > We don't need to worry about this on 64-bit machines unless they > serve for 300 million years. > > >>> (2 ** 63) / 1000 / 60 / 60 / 24 / 365 > 292471208.6775361 > > Let's convert memcg->socket_pressure to u64. > > Fixes: 8e8ae645249b8 ("mm: memcontrol: hook up vmpressure to socket pressure") > Reported-by: Neal Cardwell > Suggested-by: Andrew Morton > Signed-off-by: Kuniyuki Iwashima Acked-by: Shakeel Butt