From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 467F1C38A2D for ; Mon, 24 Oct 2022 11:03:17 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id AE04C8E0002; Mon, 24 Oct 2022 07:03:16 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id A67708E0001; Mon, 24 Oct 2022 07:03:16 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 909968E0002; Mon, 24 Oct 2022 07:03:16 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id 7D7FF8E0001 for ; Mon, 24 Oct 2022 07:03:16 -0400 (EDT) Received: from smtpin08.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 4AE93AAD6E for ; Mon, 24 Oct 2022 11:03:16 +0000 (UTC) X-FDA: 80055556392.08.1D0F286 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by imf13.hostedemail.com (Postfix) with ESMTP id C8E7520010 for ; Mon, 24 Oct 2022 11:03:15 +0000 (UTC) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id D1FA0611D8; Mon, 24 Oct 2022 11:03:14 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id E387EC433D6; Mon, 24 Oct 2022 11:03:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1666609394; bh=3p6vEdxFEex3ws6zgpDgG9A0svbChvzTuL3cIfkLL2Y=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=aEkKljZZA3CxWKUxfs4KTGpDT0B19Xva2azDkW+c+JfxB98Y/Q5wO3XAqSghfeEZB tqxCMnHa0teb3RyXnAAXUGDXZbZyY73iQphwINW6k9pnm7BGEte+qOrkW87Ezngngp HctiSoYp43kDXmOaEK+WZX7llGvIGWpgEUPUximwdJmYfJLTL/L8C4N9Y/eJFri9iV k1JWJ3Lhrrtgj8VftoNVlQXczKmbKpaMtUmFwXQIaDsN9yh5S27+YNGUFywFBiIA9S ixFedqedyu+htxeEW+CSqKSquRymkMOAjY+Y2vxYOEpo1HrhCtDvzehSZ7t+mdlpJV B6vTViv5Fl/qA== Date: Mon, 24 Oct 2022 13:03:11 +0200 From: Frederic Weisbecker To: Aaron Tomlin Cc: mtosatti@redhat.com, cl@linux.com, tglx@linutronix.de, mingo@kernel.org, peterz@infradead.org, pauld@redhat.com, neelx@redhat.com, oleksandr@natalenko.name, atomlin@atomlin.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v8 3/5] mm/vmstat: Do not queue vmstat_update if tick is stopped Message-ID: <20221024110311.GA1285913@lothringen> References: <20220924152227.819815-1-atomlin@redhat.com> <20220924152227.819815-4-atomlin@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220924152227.819815-4-atomlin@redhat.com> ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1666609395; 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=Tp/DSPF1Rgb54ai745LxiCIdzwHLT5H1/H9pXxqhpwc=; b=djB7EDHnCXQ6Z3GmDbJ/v3YNsYj161swSH2jaG2xKAA0y05zHkgBHgHM13iMoOq3WrxI4k o/tJAqSr0Lw7yw20OB/2oPKnq+eHdQpcu1oDJSjyGtx4T7fzRsn98RSEa45/pM+SALY+QJ FEri3zwVpqWPZXP7Fw0oTx0X9BfoWZ8= ARC-Authentication-Results: i=1; imf13.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=aEkKljZZ; spf=pass (imf13.hostedemail.com: domain of frederic@kernel.org designates 139.178.84.217 as permitted sender) smtp.mailfrom=frederic@kernel.org; dmarc=pass (policy=none) header.from=kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1666609395; a=rsa-sha256; cv=none; b=X98oVlUhOxdKtlxlCqvUwYL+MTYssmMXcSOF9RHqG0blnrOJpr9eHsKJ9+RutAO2se+Ruc Jb8hAoW9uh3prwHIZdIi1gaje9+XEp11wS2JGDrg8UfBm3mHMrba9If4cobZoIplyLx2Id pvRF+OE8ZWhiOaHBzyfFg+HEcrUSZVE= X-Stat-Signature: dkmhukw67haftdza1r614cguhrjtinsk X-Rspam-User: Authentication-Results: imf13.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=aEkKljZZ; spf=pass (imf13.hostedemail.com: domain of frederic@kernel.org designates 139.178.84.217 as permitted sender) smtp.mailfrom=frederic@kernel.org; dmarc=pass (policy=none) header.from=kernel.org X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: C8E7520010 X-HE-Tag: 1666609395-228430 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 Sat, Sep 24, 2022 at 04:22:25PM +0100, Aaron Tomlin wrote: > From: Marcelo Tosatti > > From the vmstat shepherd, for CPUs that have the tick stopped, do not > queue local work to flush the per-CPU vmstats, since in that case the > flush is performed on return to userspace or when entering idle. Also > cancel any delayed work on the local CPU, when entering idle on nohz > full CPUs. Per-CPU pages can be freed remotely from housekeeping CPUs. > > Signed-off-by: Marcelo Tosatti > --- > mm/vmstat.c | 18 +++++++++++++----- > 1 file changed, 13 insertions(+), 5 deletions(-) > > diff --git a/mm/vmstat.c b/mm/vmstat.c > index 472175642bd9..3b9a497965b4 100644 > --- a/mm/vmstat.c > +++ b/mm/vmstat.c > @@ -29,6 +29,7 @@ > #include > #include > #include > +#include > > #include "internal.h" > > @@ -1990,19 +1991,23 @@ static void vmstat_update(struct work_struct *w) > */ > void quiet_vmstat(void) > { > + struct delayed_work *dw; > + > if (system_state != SYSTEM_RUNNING) > return; > > if (!is_vmstat_dirty()) > return; > > + refresh_cpu_vm_stats(false); > + > /* > - * Just refresh counters and do not care about the pending delayed > - * vmstat_update. It doesn't fire that often to matter and canceling > - * it would be too expensive from this path. > - * vmstat_shepherd will take care about that for us. > + * If the tick is stopped, cancel any delayed work to avoid > + * interruptions to this CPU in the future. > */ > - refresh_cpu_vm_stats(false); > + dw = &per_cpu(vmstat_work, smp_processor_id()); > + if (delayed_work_pending(dw) && tick_nohz_tick_stopped()) > + cancel_delayed_work(dw); > } > > /* > @@ -2024,6 +2029,9 @@ static void vmstat_shepherd(struct work_struct *w) > for_each_online_cpu(cpu) { > struct delayed_work *dw = &per_cpu(vmstat_work, cpu); > > + if (tick_nohz_tick_stopped_cpu(cpu)) > + continue; > + > if (!delayed_work_pending(dw) && per_cpu(vmstat_dirty, cpu)) > queue_delayed_work_on(cpu, mm_percpu_wq, dw, 0); All these checks are racy though. You may well eventually: 1) Arm the timer after the CPU has entered in userspace 2) Not arm the timer when the CPU has entered the kernel How about converting that to an IPI instead? This should be a good candidate for the future IPI deferment. Another possible way to go is this: 1) vmstat_shepherd completely ignores nohz_full CPUs 2) vmstat_work is only ever armed locally 3) A nohz_full CPU turning its local vmstat as dirty checks if vmstat_work is pending. If not, queue it, possibly through a self IPI (IRQ_WORK) to get away with current locking context. 3) Fold on idle if dirty 4) Fold on user enter and disarm vmstat_work if pending Does that sound possible? Thanks. > > -- > 2.37.1 >