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t=1673353130; bh=aOUMcDhi1pc8g5lJzrCltSW1fWp7f/dto21aYxlxTAI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=IwOAzfPkv07dfecMpIx84BMk7joW+fAJ/GVeNKwJEczUQW4ZMC1CBF4z21IYr9rk4 EX9SneWAhsUx+EJ8RPEH86x4J7PdmHUz35fpyI5BoPuRMNP3HzK0U+7P15AVwZNKVD eGVJQXpFlyP0wr7Dw8f99iHKLpb2kIb25V11fN9mDhE9gQJg74xufGYa0ZE7UbGkj7 U5SYh7veZyzOBHZHDUmo678xz8NE56Ser749qdKJCAyLY+T/FjU/nwWq1/6rKVYZ07 o514SRRqbi61EA9955tiOmmyq/vHZRN3RtchkHRywuOl97agtO1xzNyzGrrej+uPoj e9W8820uIqc5g== Date: Tue, 10 Jan 2023 13:18:46 +0100 From: Frederic Weisbecker To: Christoph Lameter Cc: Marcelo Tosatti , atomlin@atomlin.com, tglx@linutronix.de, mingo@kernel.org, peterz@infradead.org, pauld@redhat.com, neelx@redhat.com, oleksandr@natalenko.name, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v13 2/6] mm/vmstat: Use vmstat_dirty to track CPU-specific vmstat discrepancies Message-ID: References: <20230105125218.031928326@redhat.com> <20230105125248.813825852@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: A7F6C40014 X-Rspamd-Server: rspam09 X-Rspam-User: X-Stat-Signature: f8bpbs3fdzpcipsyu7njixhucmy7ujip X-HE-Tag: 1673353132-472602 X-HE-Meta: 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 0RAuSh0M S6gaz+DWH77SbSABQtKLGq9u8LFeMpRT8dlB6OmUNDJEz1FnrD+N98iYVZHphXzrMeHlhJKqDnfkp9iM= 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: On Tue, Jan 10, 2023 at 01:06:37PM +0100, Christoph Lameter wrote: > On Thu, 5 Jan 2023, Marcelo Tosatti wrote: > > @@ -577,6 +579,9 @@ static inline void mod_zone_state(struct > > s8 __percpu *p = pcp->vm_stat_diff + item; > > long o, n, t, z; > > > > + /* cmpxchg and vmstat_mark_dirty should happen on the same CPU */ > > + preempt_disable(); > > If you are disabling preemption then why do we still need cmpxchg? > Same again below. Note I'm absolutely clueless with vmstat. But I was wondering about it as well while reviewing Marcelo's series, so git blame pointed me to: 7c83912062c801738d7d19acaf8f7fec25ea663c ("vmstat: User per cpu atomics to avoid interrupt disable / enable") And this seem to mention that this can race with IRQs as well, hence the local cmpxchg operation.