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]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 5A369CCD1AB for ; Fri, 24 Oct 2025 12:17:34 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id B91448E0089; Fri, 24 Oct 2025 08:17:33 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id B41C38E0042; Fri, 24 Oct 2025 08:17:33 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A308B8E0089; Fri, 24 Oct 2025 08:17:33 -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 88ADD8E0042 for ; Fri, 24 Oct 2025 08:17:33 -0400 (EDT) Received: from smtpin06.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 49704140E55 for ; Fri, 24 Oct 2025 12:17:33 +0000 (UTC) X-FDA: 84032908386.06.1D525D1 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf27.hostedemail.com (Postfix) with ESMTP id 8A49E40007 for ; Fri, 24 Oct 2025 12:17:31 +0000 (UTC) Authentication-Results: imf27.hostedemail.com; dkim=none; spf=pass (imf27.hostedemail.com: domain of kevin.brodsky@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=kevin.brodsky@arm.com; dmarc=pass (policy=none) header.from=arm.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1761308251; a=rsa-sha256; cv=none; b=Igy0rJYDjhBeKAE52BfD2UXRTSW7ELvBL1rhnFFc0MCi27XEJe9cPiv0TBKJVADCSoMMan qef0dHXn/esvrBq3yx6Pu5+UEFChccWw6mx9hSIjCmtKede50sMmfmHPIcKNgLZPhhm/ho azxmYAGYdLGwOgKi9OxwNPl+niSLTj8= ARC-Authentication-Results: i=1; imf27.hostedemail.com; dkim=none; spf=pass (imf27.hostedemail.com: domain of kevin.brodsky@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=kevin.brodsky@arm.com; dmarc=pass (policy=none) header.from=arm.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1761308251; 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:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=0pqn941rf59LOhvD/M25wUPoVRtPWVt8BoEPjLcQaZk=; b=cIgJHWhhjfkCnuCDdrUxHRrAP1tHdsQS9pj987KIww7UUBq1bTGP9TDooJkHB/UjExgXmB DQWOpHcAWwsSJUGJiPfvPlhhTEuYsSB6R68utwCMP2UO8nvhtEn9FQPknz/GqrURF7oXHY bIVCm7nRjPa0y0Mwn78/if7d9JU0+zg= Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id BA3FF1515; Fri, 24 Oct 2025 05:17:22 -0700 (PDT) Received: from [10.44.160.74] (e126510-lin.lund.arm.com [10.44.160.74]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 38C343F66E; Fri, 24 Oct 2025 05:17:23 -0700 (PDT) Message-ID: <35df96ba-a004-4eb4-8d26-5935892a852c@arm.com> Date: Fri, 24 Oct 2025 14:17:20 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 13/13] mm: introduce arch_wants_lazy_mmu_mode() To: David Hildenbrand , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, Alexander Gordeev , Andreas Larsson , Andrew Morton , Boris Ostrovsky , Borislav Petkov , Catalin Marinas , Christophe Leroy , Dave Hansen , "David S. Miller" , "H. Peter Anvin" , Ingo Molnar , Jann Horn , Juergen Gross , "Liam R. Howlett" , Lorenzo Stoakes , Madhavan Srinivasan , Michael Ellerman , Michal Hocko , Mike Rapoport , Nicholas Piggin , Peter Zijlstra , Ryan Roberts , Suren Baghdasaryan , Thomas Gleixner , Vlastimil Babka , Will Deacon , Yeoreum Yun , linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, sparclinux@vger.kernel.org, xen-devel@lists.xenproject.org, x86@kernel.org References: <20251015082727.2395128-1-kevin.brodsky@arm.com> <20251015082727.2395128-14-kevin.brodsky@arm.com> <3d6bba2d-9739-41d0-8f3a-f8b11620c33f@redhat.com> Content-Language: en-GB From: Kevin Brodsky In-Reply-To: <3d6bba2d-9739-41d0-8f3a-f8b11620c33f@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Stat-Signature: whkhw68gbjc14ii4urdokdkq1j85jqtj X-Rspamd-Queue-Id: 8A49E40007 X-Rspamd-Server: rspam09 X-HE-Tag: 1761308251-305657 X-HE-Meta: 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 vv3XxW9q BttFZqGSuthZNMuF7H0SGZSYs8BDVgKTJkb8KQ8/oBYTJVeBp/ejANqI2HkZ0l1OHo6oWcyimIHWXhGXST2rLUn8/NfM5W8VC+0fvlxWmOJGJLOHq0YUI1Rhf/QoHZLguBAnjS/vjhvxNrXWJ0+rU4ohrbTAMFyZ2mQB0A2wAIIAPy12vpGk5+ptF6E5lHMNpHPb/owZdCr7R7JuUtO+7fpzvb1pbaR8Izw5Ga3RQDWVhZwg= 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: List-Subscribe: List-Unsubscribe: On 23/10/2025 22:10, David Hildenbrand wrote: > On 15.10.25 10:27, Kevin Brodsky wrote: >> powerpc decides at runtime whether the lazy MMU mode should be used. >> >> To avoid the overhead associated with managing >> task_struct::lazy_mmu_state if the mode isn't used, introduce >> arch_wants_lazy_mmu_mode() and bail out of lazy_mmu_mode_* if it >> returns false. Add a default definition returning true, and an >> appropriate implementation for powerpc. >> >> Signed-off-by: Kevin Brodsky >> --- >> This patch seemed like a good idea to start with, but now I'm not so >> sure that the churn added to the generic layer is worth it. > > Exactly my thoughts :) > > I think we need evidence that this is really worth it for optimizing > out basically a counter update on powerpc. Ack, I'll drop that patch in v4 unless someone sees a better justification for it. - Kevin