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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id A47B3C53219 for ; Tue, 28 Jul 2026 09:27:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=vvFeSJ52Hy9OjYjsdGSFO6cUYL0PGqG3iOQEMzPpfqY=; b=Z9v/5o403GQJtV+igi23gWkbcv nHsqv06YWq4HBQrKXhFK1fRFGDtJrdr6k77qdT7/xW8N0zDVqNY1myDbGmL47TEFj9VFlPxYsVAjb BHF6pEOXhHROaJOubFZ0fpCOXL7h3BitS4sQ0R9wWCZRFUKNMrYCbh1lN5rDVduO11Psn//mYHpyb 8J7lM9nyjVr9uhw02lvK6+lJh64xUVx088rW/MQVfiRc/IQHcztnHdWug9UmwRD6cJIYU0nNIRStl kZ4JLK79XhsuDX1vQy4b1+HOET/l+UyvAcV0TUr59czEEMuA32KKvzdxInrK3viQgp/eEThIf4qz5 yZehYUyg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1woe5s-00000004ocp-2iTE; Tue, 28 Jul 2026 09:27:24 +0000 Received: from sea.source.kernel.org ([2600:3c0a:e001:78e:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1woe5r-00000004ocX-0agL for linux-arm-kernel@lists.infradead.org; Tue, 28 Jul 2026 09:27:23 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 97E8D436B6; Tue, 28 Jul 2026 09:27:22 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1A3981F000E9; Tue, 28 Jul 2026 09:27:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785230842; bh=vvFeSJ52Hy9OjYjsdGSFO6cUYL0PGqG3iOQEMzPpfqY=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=E3pj7Y2L4G/RAxOBSkVa7jWXgajNAmVApyA0rgIkGqGmBAIt5qVRZtxwr6AchxN9D mkmB5xfNdfLsc6YOiqyuxBG4XTpVgbzDK/WLE4szFuS/rrrWdfAWTdSApSknzc8xTM WSCgwCDNFYL05fXY8DgC2jEfljAJY6P51Ffl3DDQIUseDDEGpdhtRCI7kkHtvmKnfx bU7fU0f0NQfTnt53UbhDCDrzmRhyPeVUZt8A+f4ZnbC2KLF3GMn4E+8tZEe6rMkEhh 2gRtv8yNE/JvegoBC7fvL0IosmwDzievIsJIfgF0XXYdXXkNYqXaMhpYhYjxMCNyzV DzpcrFuMCNaXA== Date: Tue, 28 Jul 2026 10:27:17 +0100 From: Will Deacon To: Yang Shi Cc: catalin.marinas@arm.com, ryan.roberts@arm.com, cl@gentwo.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, ljs@kernel.org Subject: Re: [v8 PATCH] arm64: mm: show direct mapping use in /proc/meminfo Message-ID: References: <20260609214205.1260279-1-yang@os.amperecomputing.com> <255744ec-2a58-492c-a69a-850357440183@os.amperecomputing.com> <79d7069b-2895-4be3-a2a0-327ad3444bf3@os.amperecomputing.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <79d7069b-2895-4be3-a2a0-327ad3444bf3@os.amperecomputing.com> X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, Jul 27, 2026 at 12:50:59PM -0700, Yang Shi wrote: > On 7/22/26 4:31 AM, Will Deacon wrote: > > > Yes, it may race with memory hotplug. I missed memory hotplug for v7 > > > Sashiko. Two options to solve it: > > > > > > 1. Use atomic variables. Make lm_meminfo[NR_LM_TYPE] atomic_long_t, then > > > manipulate it with atomic ops. > > > 2. Protect it with a spin lock. > > > > > > The contention for the cache line or the spin lock should be rare since > > > memory hotplug should happen rarely. Any preference? > > I'd vote for keeping it simple and using a lock. Might be worth looking > > at the ongoing work from Lorenzo: > > > > https://lore.kernel.org/all/20260717-series-vmap-race-fix-v5-0-606a0ac6d3e5@kernel.org/ > > Thanks, Will. Took a look at Lorenzo's work. IIUC he used init_mm mmap_lock > to protect vmalloc area and linear mapping collapse on x86 in order to > serialize against ptdump. I don't think we should use init_mm mmap_lock. We > want to serialize linear mapping counter update between split and memory > hotplug, but neither of them takes init_mm mmap_lock. We can let them take > init_mm mmap_lock, but it sounds too overkilling. Hmm, but if split and hotplug don't take the mmap_lock, how are they serialised against ptdump? From what I understood, Lorenzo's patches change ptdump to take it for write in order to serialise against other walkers. Will