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[2001:8b0:10b:1231::1]) by mx.google.com with ESMTPS id k17si55952462jap.19.2019.07.29.09.26.56 for (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Mon, 29 Jul 2019 09:26:56 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of peterz@infradead.org designates 2001:8b0:10b:1231::1 as permitted sender) client-ip=2001:8b0:10b:1231::1; Authentication-Results: mx.google.com; dkim=pass header.i=@infradead.org header.s=merlin.20170209 header.b=0Bdz75ko; spf=pass (google.com: best guess record for domain of peterz@infradead.org designates 2001:8b0:10b:1231::1 as permitted sender) smtp.mailfrom=peterz@infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Transfer-Encoding: Content-Type:MIME-Version:References:Message-ID:Subject:Cc:To:From:Date: Sender:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help: List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=UR1nwN2DobERwDBbUiUS2eO5vjDIciCJ3KKzmZdKH0Q=; b=0Bdz75ko9JlIuIV7NBooLQGYXZ xKeLkiHp/upUnBeY/3RRAQ0w80wxz5hCRhdmbkGPTGDXX9l34bW83spOgXr7BkgDvyJTpD+nzx5Hk f7FHE5z3duaS40ug1H6vAfes/hnn2Ko81P07zJpuFTAL9ysk0mR3cEIhP4kdMn+6LN68BxDqEqg3v vkbk9UEmf86iZJLfE3J2DUX4/gv/0Oc6UlSCCyR2JKl/sG/g/FaCWfhkauzVmzAft4OuEWMV9uzqL q/iTWXu+CcGDHtSRVDr/0z1kzIMyyfsTEHTStTW5ZEfMyH43HSdf7OqvfzZOKEvTHMaAeCC7x0xSI V21kBB3A==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92 #3 (Red Hat Linux)) id 1hs8UA-00041z-Ot; Mon, 29 Jul 2019 16:26:55 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 75A7C20AFFE9F; Mon, 29 Jul 2019 18:26:53 +0200 (CEST) Date: Mon, 29 Jul 2019 18:26:53 +0200 From: Peter Zijlstra To: Rik van Riel Cc: Waiman Long , Ingo Molnar , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Phil Auld , Andy Lutomirski Subject: Re: [PATCH v2] sched/core: Don't use dying mm as active_mm of kthreads Message-ID: <20190729162653.GE31381@hirez.programming.kicks-ass.net> References: <20190727171047.31610-1-longman@redhat.com> <20190729085235.GT31381@hirez.programming.kicks-ass.net> <4cd17c3a-428c-37a0-b3a2-04e6195a61d5@redhat.com> <20190729150338.GF31398@hirez.programming.kicks-ass.net> <25cd74fcee33dfd0b9604a8d1612187734037394.camel@surriel.com> <20190729154419.GJ31398@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) 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 Mon, Jul 29, 2019 at 12:10:12PM -0400, Rik van Riel wrote: > On Mon, 2019-07-29 at 17:44 +0200, Peter Zijlstra wrote: > > On Mon, Jul 29, 2019 at 11:28:04AM -0400, Rik van Riel wrote: > > > On Mon, 2019-07-29 at 17:03 +0200, Peter Zijlstra wrote: > > >=20 > > > > The 'sad' part is that x86 already switches to init_mm on idle > > > > and we > > > > only keep the active_mm around for 'stupid'. > > >=20 > > > Wait, where do we do that? > >=20 > > drivers/idle/intel_idle.c: leave_mm(cpu); > > drivers/acpi/processor_idle.c: acpi_unlazy_tlb(smp_processor_id()); >=20 > This is only done for deeper c-states, isn't it? Not C1 but I forever forget where it starts doing that. IIRC it isn't too hard to hit it often, and I'm fairly sure we always do it when we hit NOHZ. > > > > Rik and Andy were working on getting that 'fixed' a while ago, > > > > not > > > > sure > > > > where that went. > > >=20 > > > My lazy TLB stuff got merged last year.=20 > >=20 > > Yes, but we never got around to getting rid of active_mm for x86, > > right? >=20 > True, we still use active_mm. Getting rid of the > active_mm refcounting alltogether did not look > entirely worthwhile the hassle. OK, clearly I forgot some of the details ;-)