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Fri, 18 Jul 2025 08:39:01 -0700 (PDT) Date: Fri, 18 Jul 2025 11:38:57 -0400 From: Johannes Weiner To: Kuniyuki Iwashima Cc: Andrew Morton , "David S. Miller" , Vladimir Davydov , Shakeel Butt , Kuniyuki Iwashima , linux-mm@kvack.org, Neal Cardwell Subject: Re: [PATCH v2] memcg: Convert memcg->socket_pressure to u64. Message-ID: <20250718153857.GB54289@cmpxchg.org> 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-Rspamd-Queue-Id: 5BD99A0008 X-Rspam-User: X-Rspamd-Server: rspam09 X-Stat-Signature: zco9473tecx631ey59kdaqnow9jwywns X-HE-Tag: 1752853143-503987 X-HE-Meta: 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 sbDEyFQq 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 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 > --- > v2: No delayed work, simply make socket_pressure u64 > > v1: https://lore.kernel.org/all/20250716042925.106239-1-kuniyu@google.com/T/#u > --- Acked-by: Johannes Weiner