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[2003:d8:2f22:1000:d72d:fd5f:4118:c70b]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-438904625f5sm136706705e9.28.2025.01.20.02.59.30 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 20 Jan 2025 02:59:30 -0800 (PST) Message-ID: <6f97f3b6-3e7b-4ff8-8d67-ef972791cccd@redhat.com> Date: Mon, 20 Jan 2025 11:59:29 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v1 0/2] How HugeTLB handle HWPoison page at truncation To: Jiaqi Yan , nao.horiguchi@gmail.com, linmiaohe@huawei.com, sidhartha.kumar@oracle.com, muchun.song@linux.dev Cc: jane.chu@oracle.com, akpm@linux-foundation.org, osalvador@suse.de, rientjes@google.com, jthoughton@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20250119180608.2132296-1-jiaqiyan@google.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: <20250119180608.2132296-1-jiaqiyan@google.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: tY340xQ5vwevbhmmLjemgTM2VZp6rYM8chJUQGk93N4_1737370772 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: rspam05 X-Rspamd-Queue-Id: 63D2780009 X-Stat-Signature: pjjmweygdgyext3cs1mnm4e59pm87uow X-Rspam-User: X-HE-Tag: 1737370775-633160 X-HE-Meta: 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 7YE/Pb8Q tthBUtYUlC0vKD75jeUWeB25pYsXs51rZmYA8DUi71k0SHu3Uu+CfQtu/hl0O65T3GUMF8rZeRIq70+z077o31pVY278n7D8i9EbedsVQYb58ytewwlV+qOVNirMFC7mTLDR+CR/ZmMLeVElAvJYNne2Vr/qAhrivTFQVGuYyIYkXSqp+WvN4zfYAm+zBG5sI2W67yJUAt6GtpU4taKwI4EtbXr5w9+nTILMC90Ro7oRPgzaybFjT1y5cKDvBx6rbtNHaiH/C1CroyTms4xBRGflsrT0ipihmP9nj7UsXQ8P4ZPvIalFxF3Zmn1PK5wONCbGpk7YxzfYnoyyg2SqlpRuXjezwln0ZI4kJMBL98bl8yaiy30EJP6BcrawJXgwzrw0yIgEli3PlWun1HWtc2gOCVjO0GNPJwaitWa+5ZI++gpPJzaj1gJwMIJ2ri62+HHTjzMcMtkeTixW852lkhM5JHA== 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 19.01.25 19:06, Jiaqi Yan wrote: > While I was working on userspace MFR via memfd [1], I spend some time to > understand what current kernel does when a HugeTLB-backing memfd is > truncated. My expectation is, if there is a HWPoison HugeTLB folio > mapped via the memfd to userspace, it will be unmapped right away but > still be kept in page cache [2]; however when the memfd is truncated to > zero or after the memfd is closed, kernel should dissolve the HWPoison > folio in the page cache, and free only the clean raw pages to buddy > allocator, excluding the poisoned raw page. > > So I wrote a hugetlb-mfr-base.c selftest and expect > 0. say nr_hugepages initially is 64 as system configuration. > 1. after MADV_HWPOISON, nr_hugepages should still be 64 as we kept even > HWPoison huge folio in page cache. free_hugepages should be > nr_hugepages minus whatever the amount in use. > 2. after truncated memfd to zero, nr_hugepages should reduced to 63 as > kernel dissolved and freed the HWPoison huge folio. free_hugepages > should also be 63. > > However, when testing at the head of mm-stable commit 2877a83e4a0a > ("mm/hugetlb: use folio->lru int demote_free_hugetlb_folios()"), I found > although free_hugepages is reduced to 63, nr_hugepages is not reduced > and stay at 64. > > Is my expectation outdated? Or is this some kind of bug? > > I assume this is a bug and then digged a little bit more. It seems there > are two issues, or two things I don't really understand. > > 1. During try_memory_failure_hugetlb, we should increased the target > in-use folio's refcount via get_hwpoison_hugetlb_folio. However, > until the end of try_memory_failure_hugetlb, this refcout is not put. > I can make sense of this given we keep in-use huge folio in page > cache. Isn't the general rule that hwpoisoned folios have a raised refcount such that they won't get freed + reused? At least that's how the buddy deals with them, and I suspect also hugetlb? > [ 1069.320976] page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x2780000 > [ 1069.320978] head: order:18 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0 > [ 1069.320980] flags: 0x400000000100044(referenced|head|hwpoison|node=0|zone=1) > [ 1069.320982] page_type: f4(hugetlb) > [ 1069.320984] raw: 0400000000100044 ffffffff8760bbc8 ffffffff8760bbc8 0000000000000000 > [ 1069.320985] raw: 0000000000000000 0000000000000000 00000001f4000000 0000000000000000 > [ 1069.320987] head: 0400000000100044 ffffffff8760bbc8 ffffffff8760bbc8 0000000000000000 > [ 1069.320988] head: 0000000000000000 0000000000000000 00000001f4000000 0000000000000000 > [ 1069.320990] head: 0400000000000012 ffffdd53de000001 ffffffffffffffff 0000000000000000 > [ 1069.320991] head: 0000000000040000 0000000000000000 00000000ffffffff 0000000000000000 > [ 1069.320992] page dumped because: track hwpoison folio's ref > > 2. Even if folio's refcount do drop to zero and we get into > free_huge_folio, it is not clear to me which part of free_huge_folio > is handling the case that folio is HWPoison. In my test what I > observed is that evantually the folio is enqueue_hugetlb_folio()-ed. How would we get a refcount of 0 if we assume the raised refcount on a hwpoisoned hugetlb folio? I'm probably missing something: are you saying that you can trigger a hwpoisoned hugetlb folio to get reallocated again, in upstream code? -- Cheers, David / dhildenb