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([2601:646:c200:7429:258b:eb0a:93b4:e6a8]) by smtp.gmail.com with ESMTPSA id l3-v6sm20102954pff.8.2018.07.31.07.29.27 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 31 Jul 2018 07:29:27 -0700 (PDT) Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (1.0) Subject: Re: [PATCH v2 11/11] mm,sched: conditionally skip lazy TLB mm refcounting From: Andy Lutomirski X-Mailer: iPhone Mail (15G77) In-Reply-To: <20180731091248.GS2494@hirez.programming.kicks-ass.net> Date: Tue, 31 Jul 2018 07:29:26 -0700 Cc: Rik van Riel , Andy Lutomirski , LKML , kernel-team , X86 ML , Vitaly Kuznetsov , Ingo Molnar , Mike Galbraith , Dave Hansen , Catalin Marinas , Benjamin Herrenschmidt Content-Transfer-Encoding: quoted-printable Message-Id: References: <20180728215357.3249-1-riel@surriel.com> <20180728215357.3249-11-riel@surriel.com> <20180729155452.37eddc11@imladris.surriel.com> <20180730095502.GG2494@hirez.programming.kicks-ass.net> <1532961011.28585.30.camel@surriel.com> <20180730162653.GM2494@hirez.programming.kicks-ass.net> <1532999155.28585.56.camel@surriel.com> <20180731091248.GS2494@hirez.programming.kicks-ass.net> To: Peter Zijlstra Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Jul 31, 2018, at 2:12 AM, Peter Zijlstra wrote: >=20 >> On Mon, Jul 30, 2018 at 09:05:55PM -0400, Rik van Riel wrote: >>> On Mon, 2018-07-30 at 18:26 +0200, Peter Zijlstra wrote: >>>=20 >>> So for ARCH_NO_ACTIVE_MM we never touch ->active_mm and therefore >>> ->active_mm =3D=3D ->mm. >>=20 >> Close, but not true for kernel threads, which have a=20 >> NULL ->mm, but a non-null ->active_mm that gets passed >> to enter_lazy_tlb(). >=20 > I'm confused on the need for this. We mark the CPU lazy, why do we still > care about this? I have considered renaming enter_lazy_tlb() to something like lazy_switch_to= _kernel_mm() (or an irqs_off variant) and making it take no parameters or ma= ybe just task pointer parameters. M=