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[37.188.130.62]) by smtp.gmail.com with ESMTPSA id l19sm3409777wmj.14.2020.04.21.05.39.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 21 Apr 2020 05:39:53 -0700 (PDT) Date: Tue, 21 Apr 2020 14:39:53 +0200 From: Michal Hocko To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Baoquan He , Oscar Salvador , Pankaj Gupta , Mike Rapoport , Anshuman Khandual Subject: Re: [PATCH RFC 2/2] mm/memory_hotplug: handle memblocks only with CONFIG_ARCH_KEEP_MEMBLOCK Message-ID: <20200421123953.GF27314@dhcp22.suse.cz> References: <20200416104707.20219-1-david@redhat.com> <20200416104707.20219-3-david@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200416104707.20219-3-david@redhat.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 16-04-20 12:47:07, David Hildenbrand wrote: > The comment in add_memory_resource() is stale: hotadd_new_pgdat() will > no longer call get_pfn_range_for_nid(), as a hotadded pgdat will simply > span no pages at all, until memory is moved to the zone/node via > move_pfn_range_to_zone() - e.g., when onlining memory blocks. > > The only archs that care about memblocks for hotplugged memory (either > for iterating over all system RAM or testing for memory validity) are > arm64, s390x, and powerpc - due to CONFIG_ARCH_KEEP_MEMBLOCK. Without > CONFIG_ARCH_KEEP_MEMBLOCK, we can simply stop messing with memblocks. OK, makes sense to me. > For s390x, it seems to be fairly easy to avoid CONFIG_ARCH_KEEP_MEMBLOCK. > arm64 could rework most code (esp., pfn_valid(), valid_phys_addr_range() > and kexec_file_load()) to not require memblocks for hotplugged > memory. E.g., as hotplugged memory has no holes and can be identified > using !early_section(), arm64's variant of pfn_valid() could be reworked > fairly easily to not require memblocks for hotadded memory. powerpc might > be more involed. I haven't checked these architectures but is the information really useful for this patch? > Cc: Andrew Morton > Cc: Michal Hocko > Cc: Baoquan He > Cc: Oscar Salvador > Cc: Pankaj Gupta > Cc: Mike Rapoport > Cc: Anshuman Khandual > Signed-off-by: David Hildenbrand Acked-by: Michal Hocko with a minor nit > - /* > - * Add new range to memblock so that when hotadd_new_pgdat() is called > - * to allocate new pgdat, get_pfn_range_for_nid() will be able to find > - * this new range and calculate total pages correctly. The range will > - * be removed at hot-remove time. > - */ > +#ifdef CONFIG_ARCH_KEEP_MEMBLOCK if (IS_ENABLED(CONFIG_ARCH_KEEP_MEMBLOCK) would be slightly nicer. This should work for all the ifedefs in this patch. > memblock_add_node(start, size, nid); > +#endif > > ret = __try_online_node(nid, false); > if (ret < 0) > @@ -1075,7 +1071,9 @@ int __ref add_memory_resource(int nid, struct resource *res) > /* rollback pgdat allocation and others */ > if (new_node) > rollback_node_hotadd(nid); > +#ifdef CONFIG_ARCH_KEEP_MEMBLOCK > memblock_remove(start, size); > +#endif > mem_hotplug_done(); > return ret; > } > @@ -1751,8 +1749,11 @@ static int __ref try_remove_memory(int nid, u64 start, u64 size) > mem_hotplug_begin(); > > arch_remove_memory(nid, start, size, NULL); > + > +#ifdef CONFIG_ARCH_KEEP_MEMBLOCK > memblock_free(start, size); > memblock_remove(start, size); > +#endif > __release_memory_resource(start, size); > > try_offline_node(nid); > -- > 2.25.1 -- Michal Hocko SUSE Labs