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[2003:cb:c719:5b00:61af:900f:3aef:3af3]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4247d0ca68esm17846255e9.30.2024.06.20.01.49.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 20 Jun 2024 01:49:47 -0700 (PDT) Message-ID: <60a075da-7c7e-4d99-ac52-059e5a17b72e@redhat.com> Date: Thu, 20 Jun 2024 10:49:46 +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 v2 2/3] mm: use folio_add_new_anon_rmap() if folio_test_anon(folio)==false To: Barry Song <21cnbao@gmail.com> Cc: akpm@linux-foundation.org, linux-mm@kvack.org, baolin.wang@linux.alibaba.com, chrisl@kernel.org, linux-kernel@vger.kernel.org, mhocko@suse.com, ryan.roberts@arm.com, shy828301@gmail.com, surenb@google.com, v-songbaohua@oppo.com, willy@infradead.org, ying.huang@intel.com, yosryahmed@google.com, yuzhao@google.com, Shuai Yuan References: <20240617231137.80726-1-21cnbao@gmail.com> <20240617231137.80726-3-21cnbao@gmail.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: 8bit On 20.06.24 10:33, Barry Song wrote: > On Thu, Jun 20, 2024 at 7:46 PM David Hildenbrand wrote: >> >> On 18.06.24 01:11, Barry Song wrote: >>> From: Barry Song >>> >>> For the !folio_test_anon(folio) case, we can now invoke folio_add_new_anon_rmap() >>> with the rmap flags set to either EXCLUSIVE or non-EXCLUSIVE. This action will >>> suppress the VM_WARN_ON_FOLIO check within __folio_add_anon_rmap() while initiating >>> the process of bringing up mTHP swapin. >>> >>> static __always_inline void __folio_add_anon_rmap(struct folio *folio, >>> struct page *page, int nr_pages, struct vm_area_struct *vma, >>> unsigned long address, rmap_t flags, enum rmap_level level) >>> { >>> ... >>> if (unlikely(!folio_test_anon(folio))) { >>> VM_WARN_ON_FOLIO(folio_test_large(folio) && >>> level != RMAP_LEVEL_PMD, folio); >>> } >>> ... >>> } >>> >>> It also improves the code’s readability. Currently, all new anonymous >>> folios calling folio_add_anon_rmap_ptes() are order-0. This ensures >>> that new folios cannot be partially exclusive; they are either entirely >>> exclusive or entirely shared. >>> >>> Suggested-by: David Hildenbrand >>> Signed-off-by: Barry Song >>> Tested-by: Shuai Yuan >>> --- >>> mm/memory.c | 8 ++++++++ >>> mm/swapfile.c | 13 +++++++++++-- >>> 2 files changed, 19 insertions(+), 2 deletions(-) >>> >>> diff --git a/mm/memory.c b/mm/memory.c >>> index 1f24ecdafe05..620654c13b2f 100644 >>> --- a/mm/memory.c >>> +++ b/mm/memory.c >>> @@ -4339,6 +4339,14 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) >>> if (unlikely(folio != swapcache && swapcache)) { >>> folio_add_new_anon_rmap(folio, vma, address, RMAP_EXCLUSIVE); >>> folio_add_lru_vma(folio, vma); >>> + } else if (!folio_test_anon(folio)) { >>> + /* >>> + * We currently only expect small !anon folios, for which we now >>> + * that they are either fully exclusive or fully shared. If we >>> + * ever get large folios here, we have to be careful. >>> + */ >>> + VM_WARN_ON_ONCE(folio_test_large(folio)); >>> + folio_add_new_anon_rmap(folio, vma, address, rmap_flags); >>> } else { >>> folio_add_anon_rmap_ptes(folio, page, nr_pages, vma, address, >>> rmap_flags); >>> diff --git a/mm/swapfile.c b/mm/swapfile.c >>> index ae1d2700f6a3..69efa1a57087 100644 >>> --- a/mm/swapfile.c >>> +++ b/mm/swapfile.c >>> @@ -1908,8 +1908,17 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd, >>> VM_BUG_ON_FOLIO(folio_test_writeback(folio), folio); >>> if (pte_swp_exclusive(old_pte)) >>> rmap_flags |= RMAP_EXCLUSIVE; >>> - >>> - folio_add_anon_rmap_pte(folio, page, vma, addr, rmap_flags); >>> + /* >>> + * We currently only expect small !anon folios, for which we now that >>> + * they are either fully exclusive or fully shared. If we ever get >>> + * large folios here, we have to be careful. >>> + */ >>> + if (!folio_test_anon(folio)) { >>> + VM_WARN_ON_ONCE(folio_test_large(folio)); >> >> (comment applies to both cases) >> >> Thinking about Hugh's comment, we should likely add here: >> >> VM_WARN_ON_FOLIO(!folio_test_locked(folio), folio); >> >> [the check we are removing from __folio_add_anon_rmap()] >> >> and document for folio_add_new_anon_rmap() in patch #1, that when >> dealing with folios that might be mapped concurrently by others, the >> folio lock must be held. > > I assume you mean something like the following for patch#1? > > diff --git a/mm/rmap.c b/mm/rmap.c > index df1a43295c85..20986b25f1b2 100644 > --- a/mm/rmap.c > +++ b/mm/rmap.c > @@ -1394,7 +1394,8 @@ void folio_add_anon_rmap_pmd(struct folio > *folio, struct page *page, > * > * Like folio_add_anon_rmap_*() but must only be called on *new* folios. > * This means the inc-and-test can be bypassed. > - * The folio does not have to be locked. > + * The folio doesn't necessarily need to be locked while it's > exclusive unless two threads > + * map it concurrently. However, the folio must be locked if it's shared. > * > * If the folio is pmd-mappable, it is accounted as a THP. > */ > @@ -1406,6 +1407,7 @@ void folio_add_new_anon_rmap(struct folio > *folio, struct vm_area_struct *vma, > int nr_pmdmapped = 0; > > VM_WARN_ON_FOLIO(folio_test_hugetlb(folio), folio); > + VM_WARN_ON_FOLIO(!exclusive && !folio_test_locked(folio), folio); For now this would likely do. I was concerned about a concurrent scenario in the exclusive case, but that shouldn't really happen I guess. -- Cheers, David / dhildenb