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([2a09:80c0:192:0:5dac:bf3d:c41:c3e7]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38a8e37d111sm11997438f8f.18.2025.01.13.01.50.20 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 13 Jan 2025 01:50:20 -0800 (PST) Message-ID: <09b71834-157b-4869-91f7-854be47b45e2@redhat.com> Date: Mon, 13 Jan 2025 10:50:19 +0100 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 3/6] mm/migrate: don't call folio_putback_active_hugetlb() on dst hugetlb folio To: Baolin Wang , linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, Andrew Morton , Muchun Song , "Matthew Wilcox (Oracle)" References: <20250110182149.746551-1-david@redhat.com> <20250110182149.746551-4-david@redhat.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: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 13.01.25 08:00, Baolin Wang wrote: > > > On 2025/1/11 02:21, David Hildenbrand wrote: >> We replaced a simple put_page() by a putback_active_hugepage() call in >> commit 3aaa76e125c1 ("mm: migrate: hugetlb: putback destination hugepage >> to active list"), to set the "active" flag on the dst hugetlb folio. >> >> Nowadays, we decoupled the "active" list from the flag, by calling the >> flag "migratable". >> >> Calling "putback" on something that wasn't allocated is weird and not >> future proof, especially if we might reach that path when migration failed >> and we just want to free the freshly allocated hugetlb folio. >> >> Let's simply set the "migratable" flag in move_hugetlb_state(), where we >> know that allocation succeeded, and use simple folio_put() to return >> our reference. >> >> Do we need the hugetlb_lock for setting that flag? Staring at other >> users of folio_set_hugetlb_migratable(), it does not look like it. After >> all, the dst folio should already be on the active list, and we are not >> modifying that list. >> >> Signed-off-by: David Hildenbrand >> --- >> mm/hugetlb.c | 5 +++++ >> mm/migrate.c | 8 ++++---- >> 2 files changed, 9 insertions(+), 4 deletions(-) >> >> diff --git a/mm/hugetlb.c b/mm/hugetlb.c >> index da98d671088d0..b24ccf8ecbf38 100644 >> --- a/mm/hugetlb.c >> +++ b/mm/hugetlb.c >> @@ -7529,6 +7529,11 @@ void move_hugetlb_state(struct folio *old_folio, struct folio *new_folio, int re >> } >> spin_unlock_irq(&hugetlb_lock); >> } >> + /* >> + * Our old folio is isolated and has "migratable" cleared until it >> + * is putback. As migration succeeded, set the new folio "migratable". >> + */ >> + folio_set_hugetlb_migratable(new_folio); >> } >> >> static void hugetlb_unshare_pmds(struct vm_area_struct *vma, >> diff --git a/mm/migrate.c b/mm/migrate.c >> index 80887cadb2774..7e23e78f1e57b 100644 >> --- a/mm/migrate.c >> +++ b/mm/migrate.c >> @@ -1542,14 +1542,14 @@ static int unmap_and_move_huge_page(new_folio_t get_new_folio, >> list_move_tail(&src->lru, ret); >> >> /* >> - * If migration was not successful and there's a freeing callback, use >> - * it. Otherwise, put_page() will drop the reference grabbed during >> - * isolation. >> + * If migration was not successful and there's a freeing callback, >> + * return the folio to that special allocator. Otherwise, simply drop >> + * our additional reference. >> */ >> if (put_new_folio) >> put_new_folio(dst, private); >> else >> - folio_putback_active_hugetlb(dst); >> + folio_put(dst); > Hi Baolin, thanks for the review! > IIUC, after the changes, so the 'dst' folio might not be added into the > 'h->hugepage_activelist' list (if the 'dst' i:s temporarily allocated), > Could this cause any side effects? Good point, so far I was under the assumption that the dst folio would already be in the active list. alloc_migration_target() and friends call alloc_hugetlb_folio_nodemask(). There are two cases: 1) We call dequeue_hugetlb_folio_nodemask() -> dequeue_hugetlb_folio_node_exact() where we add the folio to the hugepage_activelist. 2) We call alloc_migrate_hugetlb_folio() It indeed looks like we don't add them to the active list. So likely we should do: diff --git a/mm/hugetlb.c b/mm/hugetlb.c index dca4f310617a2..c6463dd7a1fc8 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -7546,7 +7546,10 @@ void move_hugetlb_state(struct folio *old_folio, struct folio *new_folio, int re * Our old folio is isolated and has "migratable" cleared until it * is putback. As migration succeeded, set the new folio "migratable". */ + spin_lock_irq(&hugetlb_lock); folio_set_hugetlb_migratable(new_folio); + list_move_tail(&new_folio->lru, &(folio_hstate(new_folio))->hugepage_activelist); + spin_unlock_irq(&hugetlb_lock); } static void hugetlb_unshare_pmds(struct vm_area_struct *vma, move_hugetlb_state() also takes care of that "temporary" handling. (I wonder if in case 1) it was a problem that the folio was already on the active list) -- Cheers, David / dhildenb