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Tsirkin" , Jason Wang , Xuan Zhuo , =?UTF-8?Q?Eugenio_P=C3=A9rez?= , Andrew Morton , Oscar Salvador , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , "Matthew Wilcox (Oracle)" References: <20250514111544.1012399-1-david@redhat.com> <20250514111544.1012399-2-david@redhat.com> <7E5BD96D-971F-4AFC-AC09-503310BE8E68@nvidia.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: <7E5BD96D-971F-4AFC-AC09-503310BE8E68@nvidia.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: wXTvpR8CHilFAN4OUp3ZaR9j9wB5eKG5NjfpYwnpH6g_1747252314 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: 9bep5mdgggh4inpqpu851171kog8jkry X-Rspam-User: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 50096C0007 X-HE-Tag: 1747252317-26321 X-HE-Meta: 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 /XyMrXkh Hh1Oa78BlutlFdsJY6x24C2KyKANGAWZvtTSJmfNkBq5s9st0zukD1DSCql8z+I4CnXbkSqpJYs2ALUSTyTNv6vAeX/AKjlHCYhn4jRTgCrESKUm8eyHf407ecJKz9D3ms8SwhVw707heXuC6bXFoIIaDLOTg7r0aixrP7B0v9RL7CKJtuYNgWjJqWhy3lw8skZ4GCmgAAyYtSv6dS62QM6MfML6P3Oy8PAzhIm81NWrC3q0QLAS3BywXe84mwXGI9UL91B8UJF9lSzrwwvkaYMtOaYmJOq+qaTpRj/3oWVx9xDlOAIe+KgiDBkyyQiNIXDeQe3OcwRyBROPaTzRZr+vafPHw8httOcrzlGhuShG1vTwBXgWbzXAu1YbrhlKBZ9QNcIsakGqMWfQ5vtXjTN59/5Tcl0eibj4S1atN85rht8PmRWiblTU/y36yZ6ljIPa9ZJeIYvm7GvE= 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: Thanks a bucnh for the review! >> + >> + if (PageOffline(page) && PageOfflineSkippable(page)) >> + continue; >> + > > Some comment like "Skippable PageOffline() pages are not migratable but are > skipped during memory offline" might help understand the change. I can add a comment like for the other cases. > > Some thoughts after reading the related code: > > offline_pages() is a little convoluted, since it has two steps to make > sure a range of memory can be offlined: > 1. start_isolate_page_range() checks unmovable (maybe not migratable > is more precise) pages using has_unmovable_pages(), but leaves unmovable > PageOffline() page handling to the driver; Right, it's best-effort. For ZONE_MOVABLE we're skipping the checks completely. I was wondering for a longer time that -- with the isolate flag being a separate bit soon :) -- we could simply isolate the whole range, and then fail if we stumble over an unmovable page during migration. That is, get rid of has_unmovable_pages() entirely. Un-doing the isolation would then properly preserve the migratetype -- no harm done? Certainly worth a look. What do you think about that? > 2. scan_movable_pages() and do_migrate_range() migrate pages and handle > different types of PageOffline() pages. Right, migrate what we can, skip these special once, and bail out on any others (at least in this patch, patch #2 restores the pre-virtio-mem behavior). > > It might make the logic cleaner if start_isolate_page_range() can > have a callback to allow driver to handle PageOffline() pages. We have to identify them repeadetly, so start_isolate_page_range() would not be sufficient. Also, callbacks are rather tricky for the case where we cannot really stabilize the page. > > Hmm, Skippable PageOffline() pages are virtio-mem specific, I wonder > why offline_pages() takes care of them. Shouldn't virtio-mem driver > handle them? > I also realize that the two steps in offline_pages()> are very similar to alloc_contig_range() and virtio-mem is using > alloc_contig_range(). I wonder if the two steps in offline_pages() > can be abstracted out and shared with virtio-mem.Yes, offline_pages()> operates at memory section granularity, different from the granularity, > pageblock size, of alloc_contig_range() used in virtio-mem, but > both are trying to check unmovable pages and migrate movable pages. Not sure I get completely what you mean. virtio-mem really wants to use alloc_contig_range() to allocate ranges it wants to unplug, because it will fail fast and allows for smaller ranges. offline_pages() is primarily also about offlining the memory section, which virtio-mem must do in order to remove the Linux memory block. > > >> folio = page_folio(page); >> >> if (!folio_try_get(folio)) >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >> index a6fe1e9b95941..325b51c905076 100644 >> --- a/mm/page_alloc.c >> +++ b/mm/page_alloc.c >> @@ -7023,12 +7023,12 @@ unsigned long __offline_isolated_pages(unsigned long start_pfn, >> continue; >> } >> /* >> - * At this point all remaining PageOffline() pages have a >> - * reference count of 0 and can simply be skipped. >> + * At this point all remaining PageOffline() pages must be >> + * "skippable" and have exactly one reference. >> */ >> if (PageOffline(page)) { >> - BUG_ON(page_count(page)); >> - BUG_ON(PageBuddy(page)); >> + WARN_ON_ONCE(!PageOfflineSkippable(page)); >> + WARN_ON_ONCE(page_count(page) != 1); >> already_offline++; >> pfn++; >> continue; >> diff --git a/mm/page_isolation.c b/mm/page_isolation.c >> index b2fc5266e3d26..debd898b794ea 100644 >> --- a/mm/page_isolation.c >> +++ b/mm/page_isolation.c >> @@ -121,16 +121,11 @@ static struct page *has_unmovable_pages(unsigned long start_pfn, unsigned long e >> continue; >> >> /* >> - * We treat all PageOffline() pages as movable when offlining >> - * to give drivers a chance to decrement their reference count >> - * in MEM_GOING_OFFLINE in order to indicate that these pages >> - * can be offlined as there are no direct references anymore. >> - * For actually unmovable PageOffline() where the driver does >> - * not support this, we will fail later when trying to actually >> - * move these pages that still have a reference count > 0. >> - * (false negatives in this function only) >> + * PageOffline() pages that are marked as "skippable" >> + * are treated like movable pages for memory offlining. >> */ >> - if ((flags & MEMORY_OFFLINE) && PageOffline(page)) >> + if ((flags & MEMORY_OFFLINE) && PageOffline(page) && >> + PageOfflineSkippable(page)) >> continue; > > With this change, we are no longer give non-virtio-mem driver a chance > to decrease PageOffline(page) refcount? Or virtio-mem is the only driver > doing this? The only in-tree driver making use of this so far, yes. There is one tweak I'll have to perform in the virtio-mem driver to cover one corner case: when force-unloading the virtio-mem driver, we have to make sure that memory blocks with fake-offline pages cannot get offlined (re-onlining would be bad). I'll fix that up. -- Cheers, David / dhildenb