From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 156B329208E for ; Wed, 14 May 2025 19:51:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747252320; cv=none; b=RB+MsEHxK0pyPYtq0nKSCr8seugQbXBSj21b6+ddUp+Ur6ogQFnE0mYtxMD1qW1lB21/ouyz7GcD91h7A1a4enyvQ9iD7QT0UZ0dmctZDUmswO00UNll87iSUbHo5yp6I4mkjsVXyN2F6Ura01iuXwcQtENTnXCLgOgfmyo+laE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747252320; c=relaxed/simple; bh=4CKWeTBIT1knGVu6jcAuG1i1LqNGaQeUgFesPH56WYY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=pZ0kTB96yAFG6mjDo9lZsngL/7FxV/7n+jA+wjZfY/8Y6caL8PmB742HmyEuZwCuCN8bjBbCsvt099H2CJN29i/Ecc3JgrI69gwEPPUDMLuyvGIPKLSRz287mxWzlOZaACkZXnkwrEsZS9W+vRzFu0BYi3+GDv/kMncK/VGUjRU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=au+w+hbT; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="au+w+hbT" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1747252316; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=KJPdhscMBkqWxz0QIEhErqluhnteOKl5RJ/gTfqAORE=; b=au+w+hbTWxaUHPm8wkh3n/IWZqH0sMqCXzM4auJP0JTXy66ZxBzHe1dDyfCt1l067jex9E 9DjY/AvjeHTUeDMDNcEcMejuQJzpmh/1lpDb2xFUi9adnlFRNlLC/HJBosSy9U4RQOTq/c kjwIJzlMpFtSG0B1UDiNo86JNxLkyHk= Received: from mail-wr1-f70.google.com (mail-wr1-f70.google.com [209.85.221.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-114-RM4juN7mOtWFXI-m3rL_VQ-1; Wed, 14 May 2025 15:51:55 -0400 X-MC-Unique: RM4juN7mOtWFXI-m3rL_VQ-1 X-Mimecast-MFC-AGG-ID: RM4juN7mOtWFXI-m3rL_VQ_1747252314 Received: by mail-wr1-f70.google.com with SMTP id ffacd0b85a97d-3a0b5d18cb7so55781f8f.2 for ; Wed, 14 May 2025 12:51:55 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1747252314; x=1747857114; h=content-transfer-encoding:in-reply-to:organization:autocrypt :content-language:from:references:cc:to:subject:user-agent :mime-version:date:message-id:x-gm-message-state:from:to:cc:subject :date:message-id:reply-to; bh=KJPdhscMBkqWxz0QIEhErqluhnteOKl5RJ/gTfqAORE=; b=CddHCQailJvkuN7mPgkdgkIWXut34xSYHQIdf7vYISr5n2D31xxfFCLMMdHRdFCT1O 93OIScC+KOzHVUJaWLiZn6CKwb2mwK5cwYxrgrpFC+on35TFAkvketGrhYuItZ4pvTJn n6bx7BWKEzhKdzNTsptDuKgwjGsaDhk/0Rg92Almr2HTrdUkDSwEvMFaZAVioiUVYbkB e7jEiejrZ1LG00kKbSiJPcgbVR8zlBIPxgFFB41mKSF75/nMWJdN1FHASjwumY212bdv tE3mbidNXnEUuvRVq9JQsbVl1tLNKilBuK74gjTSyQD6gAjklx4JplJaunQv/1l8gJN9 ITrg== X-Gm-Message-State: AOJu0Yysu/cgLZ1Bhhs9gfvLW9n/NWmwRk8wVsx9kQX8sEADE9JLQ9xh e0g/Cc8x94/YQWdtGJcyNQvUQSGVfw95njgo/9Nom8d4JhOzddw+Ug5oKOBXdeymp1AH/juMYO4 TNLUD/DGJuQdaqxO1UlS0u9PZxHVFDIuH7UaJ9vS6GxL30PW09/IpOQEvfTEP+Q== X-Gm-Gg: ASbGnctsqWxnrwJY1sTs1Gw/v9ClzIvuP2KmkpK56p/jrhwsABjqn1Y5CC7T3OejeWD 6JwJCHTrPekVJvYG4TPVHjCXD39SqERfhCr3zyLnM/Kx7JP+QpbTBmcfs3whug5LfJJ4OpXXVYN /zZ+EmbffmnnHOWd0fJYYpeCz9veTD9hdKv6mHEXROKcROhThNSxZMr/3bdGvzPFnofCJcntx4F vRSJqpUUMKkSeXQrEuz59eZ7WuztcI/pzdrHZoSDMdTAboSu4edIid9EzxlLqsLzutV0ES/jrRO BErO9agztVWxFml+EJdelmYK1hgZpSERvMMcGQY4rK9rUL2yp02V9ijPG2ses6VkgC4GhOAURya 6iuMBJxRwRv9tg/wkgBBgWpPYKYARH8nxcYOcf1Y= X-Received: by 2002:a5d:64c3:0:b0:3a2:6bc:3f25 with SMTP id ffacd0b85a97d-3a34991dab9mr4021085f8f.36.1747252314246; Wed, 14 May 2025 12:51:54 -0700 (PDT) X-Google-Smtp-Source: AGHT+IFSBbLb+wxrmL209KdMQoSzKyRwwmeEwKpF1uIgID7Mz2+GWtMlN0Mw5GJBZ6AogWzzltZPcg== X-Received: by 2002:a5d:64c3:0:b0:3a2:6bc:3f25 with SMTP id ffacd0b85a97d-3a34991dab9mr4021064f8f.36.1747252313826; Wed, 14 May 2025 12:51:53 -0700 (PDT) Received: from ?IPV6:2003:d8:2f15:6200:d485:1bcd:d708:f5df? (p200300d82f156200d4851bcdd708f5df.dip0.t-ipconnect.de. [2003:d8:2f15:6200:d485:1bcd:d708:f5df]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a3521b09c5sm199345f8f.50.2025.05.14.12.51.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 14 May 2025 12:51:53 -0700 (PDT) Message-ID: Date: Wed, 14 May 2025 21:51:52 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 1/2] mm/memory_hotplug: PG_offline_skippable for offlining memory blocks with PageOffline pages To: Zi Yan Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, virtualization@lists.linux.dev, "Michael S. 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 Content-Language: en-US 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> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit 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