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([2a09:80c0:192:0:5dac:bf3d:c41:c3e7]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-35f23c67e70sm2326824f8f.33.2024.06.10.01.56.02 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 10 Jun 2024 01:56:03 -0700 (PDT) Message-ID: <5d9583e1-3374-437d-8eea-6ab1e1400a30@redhat.com> Date: Mon, 10 Jun 2024 10:56:02 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 2/3] mm/memory_hotplug: initialize memmap of !ZONE_DEVICE with PageOffline() instead of PageReserved() To: Oscar Salvador Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-hyperv@vger.kernel.org, virtualization@lists.linux.dev, xen-devel@lists.xenproject.org, kasan-dev@googlegroups.com, Andrew Morton , Mike Rapoport , "K. Y. Srinivasan" , Haiyang Zhang , Wei Liu , Dexuan Cui , "Michael S. Tsirkin" , Jason Wang , Xuan Zhuo , =?UTF-8?Q?Eugenio_P=C3=A9rez?= , Juergen Gross , Stefano Stabellini , Oleksandr Tyshchenko , Alexander Potapenko , Marco Elver , Dmitry Vyukov References: <20240607090939.89524-1-david@redhat.com> <20240607090939.89524-3-david@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 72A6B40009 X-Stat-Signature: paq7rrkyrbg3bnorsioijdons45hu4z8 X-Rspam-User: X-Rspamd-Server: rspam11 X-HE-Tag: 1718009770-845015 X-HE-Meta: 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 a15Tv0YC 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 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: List-Subscribe: List-Unsubscribe: On 10.06.24 06:23, Oscar Salvador wrote: > On Fri, Jun 07, 2024 at 11:09:37AM +0200, David Hildenbrand wrote: >> We currently initialize the memmap such that PG_reserved is set and the >> refcount of the page is 1. In virtio-mem code, we have to manually clear >> that PG_reserved flag to make memory offlining with partially hotplugged >> memory blocks possible: has_unmovable_pages() would otherwise bail out on >> such pages. >> >> We want to avoid PG_reserved where possible and move to typed pages >> instead. Further, we want to further enlighten memory offlining code about >> PG_offline: offline pages in an online memory section. One example is >> handling managed page count adjustments in a cleaner way during memory >> offlining. >> >> So let's initialize the pages with PG_offline instead of PG_reserved. >> generic_online_page()->__free_pages_core() will now clear that flag before >> handing that memory to the buddy. >> >> Note that the page refcount is still 1 and would forbid offlining of such >> memory except when special care is take during GOING_OFFLINE as >> currently only implemented by virtio-mem. >> >> With this change, we can now get non-PageReserved() pages in the XEN >> balloon list. From what I can tell, that can already happen via >> decrease_reservation(), so that should be fine. >> >> HV-balloon should not really observe a change: partial online memory >> blocks still cannot get surprise-offlined, because the refcount of these >> PageOffline() pages is 1. >> >> Update virtio-mem, HV-balloon and XEN-balloon code to be aware that >> hotplugged pages are now PageOffline() instead of PageReserved() before >> they are handed over to the buddy. >> >> We'll leave the ZONE_DEVICE case alone for now. >> >> Signed-off-by: David Hildenbrand > >> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c >> index 27e3be75edcf7..0254059efcbe1 100644 >> --- a/mm/memory_hotplug.c >> +++ b/mm/memory_hotplug.c >> @@ -734,7 +734,7 @@ static inline void section_taint_zone_device(unsigned long pfn) >> /* >> * Associate the pfn range with the given zone, initializing the memmaps >> * and resizing the pgdat/zone data to span the added pages. After this >> - * call, all affected pages are PG_reserved. >> + * call, all affected pages are PageOffline(). >> * >> * All aligned pageblocks are initialized to the specified migratetype >> * (usually MIGRATE_MOVABLE). Besides setting the migratetype, no related >> @@ -1100,8 +1100,12 @@ int mhp_init_memmap_on_memory(unsigned long pfn, unsigned long nr_pages, >> >> move_pfn_range_to_zone(zone, pfn, nr_pages, NULL, MIGRATE_UNMOVABLE); >> >> - for (i = 0; i < nr_pages; i++) >> - SetPageVmemmapSelfHosted(pfn_to_page(pfn + i)); >> + for (i = 0; i < nr_pages; i++) { >> + struct page *page = pfn_to_page(pfn + i); >> + >> + __ClearPageOffline(page); >> + SetPageVmemmapSelfHosted(page); > > So, refresh my memory here please. > AFAIR, those VmemmapSelfHosted pages were marked Reserved before, but now, > memmap_init_range() will not mark them reserved anymore. Correct. > I do not think that is ok? I am worried about walkers getting this wrong. > > We usually skip PageReserved pages in walkers because are pages we cannot deal > with for those purposes, but with this change, we will leak > PageVmemmapSelfHosted, and I am not sure whether are ready for that. There are fortunately not that many left. I'd even say marking them (vmemmap) reserved is more wrong than right: note that ordinary vmemmap pages after memory hotplug are not reserved! Only bootmem should be reserved. Let's take at the relevant core-mm ones (arch stuff is mostly just for MMIO remapping) fs/proc/task_mmu.c: if (PageReserved(page)) fs/proc/task_mmu.c: if (PageReserved(page)) -> If we find vmemmap pages mapped into user space we already messed up seriously kernel/power/snapshot.c: if (PageReserved(page) || kernel/power/snapshot.c: if (PageReserved(page) -> There should be no change (saveable_page() would still allow saving them, highmem does not apply) mm/hugetlb_vmemmap.c: if (!PageReserved(head)) mm/hugetlb_vmemmap.c: if (PageReserved(page)) -> Wants to identify bootmem, but we exclude these PageVmemmapSelfHosted() on the splitting part already properly mm/page_alloc.c: VM_WARN_ON_ONCE(PageReserved(p)); mm/page_alloc.c: if (PageReserved(page)) -> pfn_range_valid_contig() would scan them, just like for ordinary vmemmap pages during hotplug. We'll simply fail isolating/migrating them similarly (like any unmovable allocations) later mm/page_ext.c: BUG_ON(PageReserved(page)); -> free_page_ext handling, does not apply mm/page_isolation.c: if (PageReserved(page)) -> has_unmovable_pages() should still detect them as unmovable (e.g., neither movable nor LRU). mm/page_owner.c: if (PageReserved(page)) mm/page_owner.c: if (PageReserved(page)) -> Simply page_ext_get() will return NULL instead and we'll similarly skip them mm/sparse.c: if (!PageReserved(virt_to_page(ms->usage))) { -> Detecting boot memory for ms->usage allocation, does not apply to vmemmap. virt/kvm/kvm_main.c: if (!PageReserved(page)) virt/kvm/kvm_main.c: return !PageReserved(page); -> For MMIO remapping purposes, does not apply to vmemmap > Moreover, boot memmap pages are marked as PageReserved, which would be > now inconsistent with those added during hotplug operations. Just like vmemmap pages allocated dynamically during memory hotplug. Now, really only bootmem-ones are PageReserved. > All in all, I feel uneasy about this change. I really don't want to mark these pages here PageReserved for the sake of it. Any PageReserved user that I am missing, or why we should handle these vmemmap pages differently than the ones allocated during ordinary memory hotplug? In the future, we might want to consider using a dedicated page type for them, so we can stop using a bit that doesn't allow to reliably identify them. (we should mark all vmemmap with that type then) Thanks! -- Cheers, David / dhildenb