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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C7608C433F5 for ; Wed, 29 Sep 2021 11:03:46 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 5EBA861390 for ; Wed, 29 Sep 2021 11:03:46 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 5EBA861390 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id E4DA56B00A6; Wed, 29 Sep 2021 07:03:45 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id DFDA46B00A7; Wed, 29 Sep 2021 07:03:45 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id CECBE6B00A8; Wed, 29 Sep 2021 07:03:45 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0164.hostedemail.com [216.40.44.164]) by kanga.kvack.org (Postfix) with ESMTP id C1E2E6B00A6 for ; Wed, 29 Sep 2021 07:03:45 -0400 (EDT) Received: from smtpin02.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 82146181B04A2 for ; Wed, 29 Sep 2021 11:03:45 +0000 (UTC) X-FDA: 78640325610.02.03E8AAC Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf04.hostedemail.com (Postfix) with ESMTP id 2A7BB50000B6 for ; Wed, 29 Sep 2021 11:03:45 +0000 (UTC) Received: by mail.kernel.org (Postfix) with ESMTPSA id E3BF0613CE; Wed, 29 Sep 2021 11:03:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1632913424; bh=XKEIYo+ZewR2Nn7R/NL3hozd8BvZN53o0z9on1e1NrM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=BGcadR35ExfRhxZWQxX6/CNzbtNrPLnhvwUUpQJutBpAINi3cOtBW6U5I+zVPPD28 MK8n/paiq4Mk16D1zosa/JzieW4SXYixQtnTBqUTAANPhBOeOTLalLmqLoJslA1sP3 fsSZK+uuS8ZtpwUIcI6sHc/OiPeEqUbZvsNJ7rLHFhTBvLOYQ+XjOB9SSLYD8+kXZo nm5h6W1M2jHgFzVlMKVk+a5awfZZXEtD7C4XPRGy182X5kH+nRkrXhC5JL8a9wqYTz KY62+v0xingEOuZwgLze72IZynhJ4oj51P16OWVnPF8rZAIsH99oN3x93iBS9o0uBx U05dgfN+FdQ2w== Date: Wed, 29 Sep 2021 12:03:39 +0100 From: Will Deacon To: David Hildenbrand Cc: Chris Goldsworthy , Catalin Marinas , Andrew Morton , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Sudarshan Rajagopalan Subject: Re: [RFC] arm64: mm: update max_pfn after memory hotplug Message-ID: <20210929110339.GA21510@willie-the-truck> References: <595d09279824faf1f54961cef52b745609b05d97.1632437225.git.quic_cgoldswo@quicinc.com> <20210929101028.GB21057@willie-the-truck> <13f56b37-afc7-bf6f-d544-8d6433588bf9@redhat.com> <20210929104241.GA21395@willie-the-truck> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 2A7BB50000B6 X-Stat-Signature: 46ki8rhasqeo53g859wdtffsj6xq48sc Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=BGcadR35; spf=pass (imf04.hostedemail.com: domain of will@kernel.org designates 198.145.29.99 as permitted sender) smtp.mailfrom=will@kernel.org; dmarc=pass (policy=none) header.from=kernel.org X-HE-Tag: 1632913425-647792 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 Wed, Sep 29, 2021 at 12:49:58PM +0200, David Hildenbrand wrote: > On 29.09.21 12:42, Will Deacon wrote: > > On Wed, Sep 29, 2021 at 12:29:32PM +0200, David Hildenbrand wrote: > > > On 29.09.21 12:10, Will Deacon wrote: > > > > On Thu, Sep 23, 2021 at 03:54:48PM -0700, Chris Goldsworthy wrote: > > > > > From: Sudarshan Rajagopalan > > > > > > > > > > After new memory blocks have been hotplugged, max_pfn and max_low_pfn > > > > > needs updating to reflect on new PFNs being hot added to system. > > > > > > > > > > Signed-off-by: Sudarshan Rajagopalan > > > > > Signed-off-by: Chris Goldsworthy > > > > > --- > > > > > arch/arm64/mm/mmu.c | 5 +++++ > > > > > 1 file changed, 5 insertions(+) > > > > > > > > > > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > > > > > index cfd9deb..fd85b51 100644 > > > > > --- a/arch/arm64/mm/mmu.c > > > > > +++ b/arch/arm64/mm/mmu.c > > > > > @@ -1499,6 +1499,11 @@ int arch_add_memory(int nid, u64 start, u64 size, > > > > > if (ret) > > > > > __remove_pgd_mapping(swapper_pg_dir, > > > > > __phys_to_virt(start), size); > > > > > + else { > > > > > + max_pfn = PFN_UP(start + size); > > > > > + max_low_pfn = max_pfn; > > > > > + } > > > > > > > > We use 'max_pfn' as part of the argument to set_max_mapnr(). Does that need > > > > updating as well? > > > > > > > > Do we have sufficient locking to ensure nobody is looking at max_pfn or > > > > max_low_pfn while we update them? > > > > > > Only the write side is protected by memory hotplug locking. The read side is > > > lockless -- just like all of the other pfn_to_online_page() machinery. > > > > Hmm. So the readers can see one of the variables updated but the other one > > stale? > > Yes, just like it has been on x86-64 for a long time: > > arch/x86/mm/init_64.c:update_end_of_memory_vars() > > Not sure if anyone really cares about slightly delayed updates while memory > is getting hotplugged. The users that I am aware of don't care. Thanks, I'd missed that x86 also updates max_low_pfn. So at least we're not worse off in that respect. Looking at set_max_mapnr(), I'm wondering why we need to call that at all on arm64 as 'max_mapnr' only seems to be used for nommu. Will