From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1mXKOf-005n3Z-9N for kexec@lists.infradead.org; Mon, 04 Oct 2021 09:36:34 +0000 From: David Hildenbrand Subject: [PATCH v2 2/5] memblock: improve MEMBLOCK_HOTPLUG documentation Date: Mon, 4 Oct 2021 11:36:02 +0200 Message-Id: <20211004093605.5830-3-david@redhat.com> In-Reply-To: <20211004093605.5830-1-david@redhat.com> References: <20211004093605.5830-1-david@redhat.com> MIME-Version: 1.0 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kexec" Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: linux-kernel@vger.kernel.org Cc: David Hildenbrand , Andrew Morton , Mike Rapoport , Michal Hocko , Oscar Salvador , Jianyong Wu , "Aneesh Kumar K . V" , Vineet Gupta , Geert Uytterhoeven , Huacai Chen , Jiaxun Yang , Thomas Bogendoerfer , Heiko Carstens , Vasily Gorbik , Christian Borntraeger , Eric Biederman , Arnd Bergmann , linux-snps-arc@lists.infradead.org, linux-ia64@vger.kernel.org, linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org, linux-s390@vger.kernel.org, linux-mm@kvack.org, kexec@lists.infradead.org The description of MEMBLOCK_HOTPLUG is currently short and consequently misleading: we're actually dealing with a memory region that might get hotunplugged later (i.e., the platform+firmware supports it), yet it is indicated in the firmware-provided memory map as system ram that will just get used by the system for any purpose when not taking special care. The firmware marked this memory region as a hot(un)plugged (e.g., hotplugged before reboot), implying that it might get hotunplugged again later. Whether we consider this information depends on the "movable_node" kernel commandline parameter: only with "movable_node" set, we'll try keeping this memory hotunpluggable, for example, by not serving early allocations from this memory region and by letting the buddy manage it using the ZONE_MOVABLE. Let's make this clearer by extending the documentation. Note: kexec *has to* indicate this memory to the second kernel. With "movable_node" set, we don't want to place kexec-images on this memory. Without "movable_node" set, we don't care and can place kexec-images on this memory. In both cases, after successful memory hotunplug, kexec has to be re-armed to update the memory map for the second kernel and to place the kexec-images somewhere else. Signed-off-by: David Hildenbrand --- include/linux/memblock.h | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/include/linux/memblock.h b/include/linux/memblock.h index 34de69b3b8ba..4ee8dd2d63a7 100644 --- a/include/linux/memblock.h +++ b/include/linux/memblock.h @@ -28,7 +28,11 @@ extern unsigned long long max_possible_pfn; /** * enum memblock_flags - definition of memory region attributes * @MEMBLOCK_NONE: no special request - * @MEMBLOCK_HOTPLUG: hotpluggable region + * @MEMBLOCK_HOTPLUG: memory region indicated in the firmware-provided memory + * map during early boot as hot(un)pluggable system RAM (e.g., memory range + * that might get hotunplugged later). With "movable_node" set on the kernel + * commandline, try keeping this memory region hotunpluggable. Does not apply + * to memblocks added ("hotplugged") after early boot. * @MEMBLOCK_MIRROR: mirrored region * @MEMBLOCK_NOMAP: don't add to kernel direct mapping and treat as * reserved in the memory map; refer to memblock_mark_nomap() description -- 2.31.1 _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec