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 X-Spam-Level: X-Spam-Status: No, score=-2.4 required=3.0 tests=DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,T_DKIM_INVALID, USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C62A9FD21E1 for ; Mon, 30 Jul 2018 09:55:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7373420893 for ; Mon, 30 Jul 2018 09:55:26 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="FUB37tPp" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7373420893 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727010AbeG3L3g (ORCPT ); Mon, 30 Jul 2018 07:29:36 -0400 Received: from merlin.infradead.org ([205.233.59.134]:41012 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726709AbeG3L3g (ORCPT ); Mon, 30 Jul 2018 07:29:36 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding: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=rYRMSz+HVK4nu0hq6MV3VwjWNnI+ajHDuoPoW28AXRo=; b=FUB37tPp56tHLNggLhGeDnm5b S4dP2Gk2oTB87ZThJXH4z5wovygsJFWXxkSYZRVQ+FYGnhrDy2huPPGkmdXjel5eAKZksWH/4Ruf0 Lx1Qpy/ujs6fC5bATZtygy7vH0SuXuqTB1T1TktQW8KBeLWW1WRGSalVURwLrk8Ep/fmqt201G9KQ VAid49MT8jGK9LmCX4I9H1V7ULOCqsXvKK/cDR5FpX5r5NgTCmgdt3dnkX5/YBUNoqzV2fvLr9Ujy M3QqU1Iat7bGvcZZttrdUNfq2A1Lk78+1q3z+X7m2gk8VGHW5Cy0ZOrqudzAhM9W/3+NY9qm1kZlT R7IKIkCXg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1fk4tO-0005Os-0j; Mon, 30 Jul 2018 09:55:06 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id E338F202883BF; Mon, 30 Jul 2018 11:55:02 +0200 (CEST) Date: Mon, 30 Jul 2018 11:55:02 +0200 From: Peter Zijlstra To: Rik van Riel Cc: Andy Lutomirski , LKML , kernel-team , X86 ML , Vitaly Kuznetsov , Ingo Molnar , Mike Galbraith , Dave Hansen , Catalin Marinas , Benjamin Herrenschmidt Subject: Re: [PATCH v2 11/11] mm,sched: conditionally skip lazy TLB mm refcounting Message-ID: <20180730095502.GG2494@hirez.programming.kicks-ass.net> References: <20180728215357.3249-1-riel@surriel.com> <20180728215357.3249-11-riel@surriel.com> <20180729155452.37eddc11@imladris.surriel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180729155452.37eddc11@imladris.surriel.com> User-Agent: Mutt/1.10.0 (2018-05-17) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Jul 29, 2018 at 03:54:52PM -0400, Rik van Riel wrote: > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index c45de46fdf10..11724c9e88b0 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -2691,7 +2691,7 @@ static struct rq *finish_task_switch(struct task_struct *prev) > */ > if (mm) { > membarrier_mm_sync_core_before_usermode(mm); > - mmdrop(mm); > + drop_lazy_mm(mm); > } > if (unlikely(prev_state == TASK_DEAD)) { > if (prev->sched_class->task_dead) > @@ -2805,7 +2805,7 @@ context_switch(struct rq *rq, struct task_struct *prev, > */ > if (!mm) { > next->active_mm = oldmm; > - mmgrab(oldmm); > + grab_lazy_mm(oldmm); > enter_lazy_tlb(oldmm, next); > } else > switch_mm_irqs_off(oldmm, mm, next); What happened to the rework I did there? That not only avoided fiddling with active_mm, but also avoids grab/drop cycles for the other architectures when doing task->kthread->kthread->task things. I agree with Andy that if you avoid the refcount fiddling, then you should also not muck with active_mm. That is, if you keep active_mm for now (which seems a reasonable first step) then at least ensure you keep ->mm == ->active_mm at all times.