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=-0.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no 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 E5CEBC34022 for ; Wed, 19 Feb 2020 21:46:48 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id A2BB524671 for ; Wed, 19 Feb 2020 21:46:48 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="Muu7wuj9" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A2BB524671 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 3DC936B0008; Wed, 19 Feb 2020 16:46:48 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 38DE76B007B; Wed, 19 Feb 2020 16:46:48 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 2A2D56B007D; Wed, 19 Feb 2020 16:46:48 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0247.hostedemail.com [216.40.44.247]) by kanga.kvack.org (Postfix) with ESMTP id 0FDCB6B0008 for ; Wed, 19 Feb 2020 16:46:48 -0500 (EST) Received: from smtpin24.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id D40D9180AD815 for ; Wed, 19 Feb 2020 21:46:47 +0000 (UTC) X-FDA: 76508211654.24.son36_7582dc60bfa3a X-HE-Tag: son36_7582dc60bfa3a X-Filterd-Recvd-Size: 3236 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf30.hostedemail.com (Postfix) with ESMTP for ; Wed, 19 Feb 2020 21:46:47 +0000 (UTC) Received: from X1 (nat-ab2241.sltdut.senawave.net [162.218.216.4]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 7624424654; Wed, 19 Feb 2020 21:46:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1582148806; bh=HxfYRjJj58z+qAAsFwPuZfJ0KZbNY+dKSV+60i8qVIs=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=Muu7wuj9ri3Wvcl3mc3d8sk4smKoASDoa02eUn9plYSjI6agD+f8aGFYssTJjKK05 dExvMbtjpSDHMgolAcpGJveYtVAWzY4uSeZlmuieDqqfaCRrfzk1yP2uHek5RCXGkW HgHG5zDMhlIzFXL1XRhWZW9L3976VnXD5qU+VTjk= Date: Wed, 19 Feb 2020 13:46:45 -0800 From: Andrew Morton To: Michal Hocko Cc: kkabe@vega.pgw.jp, bhe@redhat.com, david@redhat.com, osalvador@suse.de, bugzilla-daemon@bugzilla.kernel.org, richardw.yang@linux.intel.com, n-horiguchi@ah.jp.nec.com, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [RFC PATCH] memory_hotplug: disable the functionality for 32b (was: Re: [Bug 206401] kernel panic on Hyper-V after 5 minutes due to) memory hot-add Message-Id: <20200219134645.7430db57e0e59f69e7386f46@linux-foundation.org> In-Reply-To: <20200218100532.GA4151@dhcp22.suse.cz> References: <20200218084700.GD21113@dhcp22.suse.cz> <200218181900.M0115079@vega.pgw.jp> <20200218100532.GA4151@dhcp22.suse.cz> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.32; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit 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 Tue, 18 Feb 2020 11:05:32 +0100 Michal Hocko wrote: > Subject: [PATCH] memory_hotplug: disable the functionality for 32b > > Memory hotlug is broken for 32b systems at least since c6f03e2903c9 > ("mm, memory_hotplug: remove zone restrictions") which has considerably > reworked how can be memory associated with movable/kernel zones. The > same is not really trivial to achieve in 32b where only lowmem is the > kernel zone. While we can tweak this immediate problem around there are > likely other land mines hidden at other places. > > It is also quite dubious that there is a real usecase for the memory > hotplug on 32b in the first place. Low memory is just too small to be > hotplugable (for hot add) and generally unusable for hotremove. Adding > more memory to highmem is also dubious because it would increase the > low mem or vmalloc space pressure for memmaps. > > Restrict the functionality to 64b systems. This will help future > development to focus on usecases that have real life application. We > can remove this restriction in future in presence of a real life usecase > of course but until then make it explicit that hotplug on 32b is broken > and requires a non trivial amount of work to fix. (cc linux-arch) (and linux-arm-kernel, as ARM is a major 32-bit user) Does anyone see a problem with disabling memory hotplug on 32-bit builds?