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=-3.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 001C3C433DF for ; Thu, 4 Jun 2020 23:48:54 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id AFFD1208B6 for ; Thu, 4 Jun 2020 23:48:54 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="jEEhM7Wn" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AFFD1208B6 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 5991F280030; Thu, 4 Jun 2020 19:48:54 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 54A23280005; Thu, 4 Jun 2020 19:48:54 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 48698280030; Thu, 4 Jun 2020 19:48:54 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0207.hostedemail.com [216.40.44.207]) by kanga.kvack.org (Postfix) with ESMTP id 33F87280005 for ; Thu, 4 Jun 2020 19:48:54 -0400 (EDT) Received: from smtpin12.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id E342C3749 for ; Thu, 4 Jun 2020 23:48:53 +0000 (UTC) X-FDA: 76893172146.12.owl55_2e001d726d9b Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin12.hostedemail.com (Postfix) with ESMTP id BD25E18052F78 for ; Thu, 4 Jun 2020 23:48:53 +0000 (UTC) X-HE-Tag: owl55_2e001d726d9b X-Filterd-Recvd-Size: 3914 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf25.hostedemail.com (Postfix) with ESMTP for ; Thu, 4 Jun 2020 23:48:53 +0000 (UTC) Received: from localhost.localdomain (c-73-231-172-41.hsd1.ca.comcast.net [73.231.172.41]) (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 42DCB208C3; Thu, 4 Jun 2020 23:48:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1591314532; bh=6wYDJlLsiqfWVvdxuDErxU85JKWJRIvHyyOBGa10/RE=; h=Date:From:To:Subject:In-Reply-To:From; b=jEEhM7WnzY8lnc0mMIUv+4K9kOCn09wUH5Cv3872tmFnFW/VwVkYE4FGG9TxpUNPB I3naqG+7/PxXHk5HxUgj2aF18VJH68TmAVXu4ifCWl4jbdjkul+xp5Fggs6t5+W9RV DI7YD8ExcGRffOnckiPVFH1kDxkk6shqNeJ5N93o= Date: Thu, 04 Jun 2020 16:48:51 -0700 From: Andrew Morton To: akpm@linux-foundation.org, bhe@redhat.com, david@redhat.com, linux-mm@kvack.org, mhocko@kernel.org, mhocko@suse.com, mm-commits@vger.kernel.org, n-horiguchi@ah.jp.nec.com, osalvador@suse.de, richardw.yang@linux.intel.com, robin.murphy@arm.com, torvalds@linux-foundation.org, vamshi.k.sthambamkadi@gmail.com Subject: [patch 050/127] mm/memory_hotplug: disable the functionality for 32b Message-ID: <20200604234851.FvqR8M-jA%akpm@linux-foundation.org> In-Reply-To: <20200604164523.e15f3177f4b69dcb4f2534a1@linux-foundation.org> User-Agent: s-nail v14.8.16 X-Rspamd-Queue-Id: BD25E18052F78 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam04 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: From: Michal Hocko Subject: mm/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. Robin said: : 32-bit Arm doesn't support memory hotplug, and as far as I'm aware there's : little likelihood of it ever wanting to. FWIW it looks like SuperH is the : only pure-32-bit architecture to have hotplug support at all. Link: http://lkml.kernel.org/r/20200218100532.GA4151@dhcp22.suse.cz Link: https://bugzilla.kernel.org/show_bug.cgi?id=206401 Signed-off-by: Michal Hocko Acked-by: David Hildenbrand Acked-by: Baoquan He Cc: Wei Yang Cc: Naoya Horiguchi Cc: Oscar Salvador Cc: Robin Murphy Cc: Vamshi K Sthambamkadi Signed-off-by: Andrew Morton --- mm/Kconfig | 1 + 1 file changed, 1 insertion(+) --- a/mm/Kconfig~memory_hotplug-disable-the-functionality-for-32b +++ a/mm/Kconfig @@ -158,6 +158,7 @@ config MEMORY_HOTPLUG bool "Allow for memory hot-add" depends on SPARSEMEM || X86_64_ACPI_NUMA depends on ARCH_ENABLE_MEMORY_HOTPLUG + depends on 64BIT || BROKEN select NUMA_KEEP_MEMINFO if NUMA config MEMORY_HOTPLUG_SPARSE _