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[82.17.115.212]) by smtp.gmail.com with ESMTPSA id x15-20020a5d490f000000b002205a5de337sm13271283wrq.102.2022.08.17.09.48.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 17 Aug 2022 09:48:45 -0700 (PDT) Date: Wed, 17 Aug 2022 17:48:44 +0100 From: Aaron Tomlin To: Marcelo Tosatti Cc: frederic@kernel.org, cl@linux.com, tglx@linutronix.de, mingo@kernel.org, peterz@infradead.org, pauld@redhat.com, neelx@redhat.com, oleksandr@natalenko.name, atomlin@atomlin.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v6 2/2] tick/sched: Ensure quiet_vmstat() is called when the idle tick was stopped too Message-ID: <20220817164844.zyypokjmzjfznuhu@ava.usersys.com> X-PGP-Key: http://pgp.mit.edu/pks/lookup?search=atomlin%40redhat.com X-PGP-Fingerprint: 7906 84EB FA8A 9638 8D1E 6E9B E2DE 9658 19CC 77D6 References: <20220808194820.676246-1-atomlin@redhat.com> <20220808194820.676246-3-atomlin@redhat.com> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1660754930; a=rsa-sha256; cv=none; b=TSrZErYc/rm9B7yZXyL4cZNLkPT2ur6WKa51Mgezrg+0N3U+ukwR3R0VsGqytl+8oQxYqN QaAlzdqTRqsdRcEuWAJ5ncQ3vz7t3VsSoieTZ7S+RhpJ0rv2wCPHEMfY1dQhJtfis1wDFY ZYulzCtXo3jcweYAQ2klVDmpx8mRi3g= ARC-Authentication-Results: i=1; imf23.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=TpzD3g3G; spf=pass (imf23.hostedemail.com: domain of atomlin@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=atomlin@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1660754930; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=5DFVkzD/EoUahef5UFlOF/HjlPxQz4n3aaKR684FIcs=; b=bKk1OvLuWvBUM6CJHQ9ib2DUMLiseWEZBiHMFpXfPKR1VuRTucPM0sU35gP3xjpmOSBDFV 96otFCu5FjnfyMl5y+FJ+SwweanvOCS5lDf7DRCOsR+flkhLp6fLs1x0jI4LjDCyQiyQjP 6dkmd9S19d5M3nTObr+xNgnx24hyKB4= Authentication-Results: imf23.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=TpzD3g3G; spf=pass (imf23.hostedemail.com: domain of atomlin@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=atomlin@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 6E309140063 X-Stat-Signature: mckxjpcwm1dcatbkt8phamtjkazb8uef X-Rspam-User: X-HE-Tag: 1660754930-797130 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 2022-08-16 15:11 -0300, Marcelo Tosatti wrote: > Aaron, > > It is also necessary to remove the delayed_work_pending check from > quiet_vmstat: > > @@ -1987,10 +1970,7 @@ void quiet_vmstat(void) > if (system_state != SYSTEM_RUNNING) > return; > > - if (!delayed_work_pending(this_cpu_ptr(&vmstat_work))) > - return; > - > - if (!need_update(smp_processor_id())) > + if (!__this_cpu_read(vmstat_dirty)) > return; > > > Because, consider the following situation: > > > vmstat_shepherd CPU nohz_full CPU > > > vmstat_dirty = false > enter nohz_full > return to userspace > check vmstat_dirty, unset, > delayed work cancelled. > dirties per-CPU vmstats > vmstat_dirty = true > return to userspace > (quiet_vmstat will skip > clearing stats because > delayed work was not queued). Hi Marcelo, Yes, I agree - the above scenario can occur. Kind regards, -- Aaron Tomlin