From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: + memory_hotplug-disable-the-functionality-for-32b.patch added to -mm tree Date: Thu, 04 Jun 2020 12:59:13 -0700 Message-ID: <20200604195913.KsECDwHeH%akpm@linux-foundation.org> References: <20200603155549.e041363450869eaae4c7f05b@linux-foundation.org> Reply-To: linux-kernel@vger.kernel.org Return-path: Received: from mail.kernel.org ([198.145.29.99]:57112 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726026AbgFDT7P (ORCPT ); Thu, 4 Jun 2020 15:59:15 -0400 In-Reply-To: <20200603155549.e041363450869eaae4c7f05b@linux-foundation.org> Sender: mm-commits-owner@vger.kernel.org List-Id: mm-commits@vger.kernel.org To: bhe@redhat.com, david@redhat.com, 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, vamshi.k.sthambamkadi@gmail.com The patch titled Subject: mm/memory_hotplug: disable the functionality for 32b has been added to the -mm tree. Its filename is memory_hotplug-disable-the-functionality-for-32b.patch This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/memory_hotplug-disable-the-functionality-for-32b.patch and later at http://ozlabs.org/~akpm/mmotm/broken-out/memory_hotplug-disable-the-functionality-for-32b.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ 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 @@ -155,6 +155,7 @@ 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 _ Patches currently in -mm which might be from mhocko@kernel.org are memory_hotplug-disable-the-functionality-for-32b.patch