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[84.156.64.103]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-42577a0dda2sm18588475e9.0.2024.06.29.07.38.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 29 Jun 2024 07:38:48 -0700 (PDT) Message-ID: Date: Sat, 29 Jun 2024 16:38:47 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/4] mm: not __SetPageReserved on initializing hot-plugged memory To: Wei Yang Cc: akpm@linux-foundation.org, rppt@kernel.org, linux-mm@kvack.org, Nathan Zimmer References: <20240629013322.12364-1-richard.weiyang@gmail.com> <20240629013322.12364-2-richard.weiyang@gmail.com> <9e05d9da-36bd-4094-93d7-1c19eb77df1e@redhat.com> <20240629083222.35mebt7kqxiepsgg@master> 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: <20240629083222.35mebt7kqxiepsgg@master> 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-Server: rspam03 X-Rspam-User: X-Rspamd-Queue-Id: 22F342001C X-Stat-Signature: zfz14pzjnbjetdq6995mk7zjxpsrrrm8 X-HE-Tag: 1719671933-680592 X-HE-Meta: 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 fGSI6/Zi RLPGVdM9v00k+pQOZv2Y0l/TXJUdOX6K8onrbdcEB5QXQdZkkVFfn+uZqmZlsAmTiMur8siMeCeLu0402svFhYogJfY0hsC4RDoSub6XIZHWGA15HDHBqJe/PGX+hxdkY7Vk9tTO/ylg2rcr9ZsZsQoa/D6P+VyrH/V8ecYuuuG9qRtzBOrkbCTU+P3VZQeXwarCf7XVL7IFaC6hXS0H4a8GZCaOk1nSvvMBhXz7Q0BRm6LTWCRYilWCvKeyGwS9lyfK2a49F42B7OJ5Xyh/xH7dCyYXjgPPbw89riZ2Ptma1bIqq9Pus+TMqvMUhR+EdsX2zZh4sZpvGfXYJrf3mxHWumRIMZGI4RNnevyZ2oUH9pawCkYij/OnkxuG9OA9df+FvRzRBlb79t1dA42ywtgCj51SCg1XgjWup+hHaSt9j+Dze9qgk9bPeSWL9YtPRnnu6lpm0q/LkpVcTh43kB1+fmbhORTbMzoHp+Cpjb4qXqnI= 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 29.06.24 10:32, Wei Yang wrote: > On Sat, Jun 29, 2024 at 08:19:49AM +0200, David Hildenbrand wrote: >> On 29.06.24 03:33, Wei Yang wrote: >>> Initialize all pages reserved is an ancient behavior. >>> >>> Since commit 92923ca3aace ("mm: meminit: only set page reserved in the >>> memblock region"), SetPageReserved is removed from >>> __init_single_page(). Only those reserved pages are marked PG_reserved. >>> >>> But we still set PG_reserved on offline and check it on online. >>> >>> Following two commits removed both of them: >>> >>> * Commit 0ee5f4f31d36 ("mm/page_alloc.c: don't set pages PageReserved() >>> when offlining") removed the set on offline. >>> * Commit 5ecae6359e3a ("mm/memory_hotplug: drop PageReserved() check in >>> online_pages_range()") removed the check on online. >>> >>> This means we set PG_reserved for hot-plugged memory at initialization >>> is not helpful and a little different from bootmem initialization path. >>> Now we can remove it. >> >> It's not that easy for ZONE_DEVICE. >> >> Also, see mm/mm-stable >> >> commit 3dadec1babf9eee0c67c967df931d6f0cb124a04 >> Author: David Hildenbrand >> Date: Fri Jun 7 11:09:36 2024 +0200 >> >> mm: pass meminit_context to __free_pages_core() >> >> Patch series "mm/memory_hotplug: use PageOffline() instead of >> PageReserved() for !ZONE_DEVICE". >> >> >> commit b873faaa609ab44c223b2327f55d2b6a2ba4ca9c >> Author: David Hildenbrand >> Date: Fri Jun 7 11:09:37 2024 +0200 >> >> mm/memory_hotplug: initialize memmap of !ZONE_DEVICE with PageOffline() >> instead of PageReserved() >> > > Let me try to understand this. > > You also tries to get rid of PG_reserved but you want PG_offline instead, > because this benefit virtio-mem, right? We now make proper use of PG_offline. All hotplugged pages start out PG_offline once we turn the section online. Only the ones that actually get exposed to the buddy -- actually get onlined -- get PG_offline cleared. A side effect of that is less hacks for virtio-mem, and more natural handling for the other ballooning drivers that hotplug memory. In the future, I'm planning on moving more fake-offlining code from virtio-mem the core, making use of more PG_offline in memory. For now, it's stops the PG_reserved use while maintaining the same semantics as before: the page content and "struct page" is not to be touched by anybody except the "owner". > > But I don't get why PG_offline is wrong for ZONE_DEVICE. I may miss some > knowledge for it. I suggest you take a look at the PG_offline documentation. ZONE_DEVICE are certainly not logically offline pages. They will never be considered online as part of online sections. But they will never be handed to the buddy. Maybe we want a dedicate page type for them in the future, not sure. We can right now identify them reliably using the zone idx. Using a page type right now is very likely not possible, because we might be using the page->_mapcount in rmap code when mapping some of them to user space. If we want to get rid of the PG_reserved for them right now, we'll have to make sure all existing PageReserved checks won't be degraded. For example, drivers/vfio/vfio_iommu_type1.c might need some work (no sure). The KVM one in kvm_pfn_to_refcounted_page() should already be fine, because they really want to refcount them. A lot of other ones like can_gather_numa_stats(), already refuse is_zone_device_page() manually, and maybe we want to factor both checks out into a separate function like "is_special_reserved_page()" or sth like that. -- Cheers, David / dhildenb