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[2003:cb:c710:8800:a73c:ec5b:c02c:5e0b]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-42158111143sm46303815e9.20.2024.06.06.00.39.14 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 06 Jun 2024 00:39:15 -0700 (PDT) Message-ID: <19590664-5190-4d30-ba0d-ec9d0ea373d3@redhat.com> Date: Thu, 6 Jun 2024 09:39:14 +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] mm/gup: don't check page lru flag before draining it To: yangge1116 , akpm@linux-foundation.org, Matthew Wilcox Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, baolin.wang@linux.alibaba.com, liuzixing@hygon.cn References: <1717498121-20926-1-git-send-email-yangge1116@126.com> <0d7a4405-9a2e-4bd1-ba89-a31486155233@redhat.com> <776de760-e817-43b2-bd00-8ce96f4e37a8@redhat.com> <7063920f-963a-4b3e-a3f3-c5cc227bc877@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: 8bit On 06.06.24 03:35, yangge1116 wrote: > > > 在 2024/6/5 下午5:53, David Hildenbrand 写道: >> On 05.06.24 11:41, David Hildenbrand wrote: >>> On 05.06.24 03:18, yangge1116 wrote: >>>> >>>> >>>> 在 2024/6/4 下午9:47, David Hildenbrand 写道: >>>>> On 04.06.24 12:48, yangge1116@126.com wrote: >>>>>> From: yangge >>>>>> >>>>>> If a page is added in pagevec, its ref count increases one, remove >>>>>> the page from pagevec decreases one. Page migration requires the >>>>>> page is not referenced by others except page mapping. Before >>>>>> migrating a page, we should try to drain the page from pagevec in >>>>>> case the page is in it, however, folio_test_lru() is not sufficient >>>>>> to tell whether the page is in pagevec or not, if the page is in >>>>>> pagevec, the migration will fail. >>>>>> >>>>>> Remove the condition and drain lru once to ensure the page is not >>>>>> referenced by pagevec. >>>>> >>>>> What you are saying is that we might have a page on which >>>>> folio_test_lru() succeeds, that was added to one of the cpu_fbatches, >>>>> correct? >>>> >>>> Yes >>>> >>>>> >>>>> Can you describe under which circumstances that happens? >>>>> >>>> >>>> If we call folio_activate() to move a page from inactive LRU list to >>>> active LRU list, the page is not only in LRU list, but also in one of >>>> the cpu_fbatches. >>>> >>>> void folio_activate(struct folio *folio) >>>> { >>>>        if (folio_test_lru(folio) && !folio_test_active(folio) && >>>>            !folio_test_unevictable(folio)) { >>>>            struct folio_batch *fbatch; >>>> >>>>            folio_get(folio); >>>>            //After this, folio is in LRU list, and its ref count have >>>> increased one. >>>> >>>>            local_lock(&cpu_fbatches.lock); >>>>            fbatch = this_cpu_ptr(&cpu_fbatches.activate); >>>>            folio_batch_add_and_move(fbatch, folio, folio_activate_fn); >>>>            local_unlock(&cpu_fbatches.lock); >>>>        } >>>> } >>> >>> Interesting, the !SMP variant does the folio_test_clear_lru(). >>> >>> It would be really helpful if we could reliably identify whether LRU >>> batching code has a raised reference on a folio. >>> >>> We have the same scenario in >>> * folio_deactivate() >>> * folio_mark_lazyfree() >>> >>> In folio_batch_move_lru() we do the folio_test_clear_lru(folio). >>> >>> No expert on that code, I'm wondering if we could move the >>> folio_test_clear_lru() out, such that we can more reliably identify >>> whether a folio is on the LRU batch or not. >> >> I'm sure there would be something extremely broken with the following >> (I don't know what I'm doing ;) ), but I wonder if there would be a way >> to make something like that work (and perform well enough?). >> >> diff --git a/mm/swap.c b/mm/swap.c >> index 67786cb771305..642e471c3ec5a 100644 >> --- a/mm/swap.c >> +++ b/mm/swap.c >> @@ -212,10 +212,6 @@ static void folio_batch_move_lru(struct folio_batch >> *fbatch, move_fn_t move_fn) >>         for (i = 0; i < folio_batch_count(fbatch); i++) { >>                 struct folio *folio = fbatch->folios[i]; >> >> -               /* block memcg migration while the folio moves between >> lru */ >> -               if (move_fn != lru_add_fn && !folio_test_clear_lru(folio)) >> -                       continue; >> - >>                 folio_lruvec_relock_irqsave(folio, &lruvec, &flags); >>                 move_fn(lruvec, folio); >> >> @@ -255,8 +251,9 @@ static void lru_move_tail_fn(struct lruvec *lruvec, >> struct folio *folio) >>   */ >>  void folio_rotate_reclaimable(struct folio *folio) >>  { >> -       if (!folio_test_locked(folio) && !folio_test_dirty(folio) && >> -           !folio_test_unevictable(folio) && folio_test_lru(folio)) { >> +       if (folio_test_lru(folio) && !folio_test_locked(folio) && >> +           !folio_test_dirty(folio) && !folio_test_unevictable(folio) && >> +           folio_test_clear_lru(folio)) { >>                 struct folio_batch *fbatch; >>                 unsigned long flags; >> >> @@ -354,7 +351,7 @@ static void folio_activate_drain(int cpu) >>  void folio_activate(struct folio *folio) >>  { >>         if (folio_test_lru(folio) && !folio_test_active(folio) && >> -           !folio_test_unevictable(folio)) { >> +           !folio_test_unevictable(folio) && >> folio_test_clear_lru(folio)) { >>                 struct folio_batch *fbatch; >> >>                 folio_get(folio); >> @@ -699,6 +696,8 @@ void deactivate_file_folio(struct folio *folio) >>         /* Deactivating an unevictable folio will not accelerate >> reclaim */ >>         if (folio_test_unevictable(folio)) >>                 return; >> +       if (!folio_test_clear_lru(folio)) >> +               return; >> >>         folio_get(folio); >>         local_lock(&cpu_fbatches.lock); >> @@ -718,7 +717,8 @@ void deactivate_file_folio(struct folio *folio) >>  void folio_deactivate(struct folio *folio) >>  { >>         if (folio_test_lru(folio) && !folio_test_unevictable(folio) && >> -           (folio_test_active(folio) || lru_gen_enabled())) { >> +           (folio_test_active(folio) || lru_gen_enabled()) && >> +           folio_test_clear_lru(folio)) { >>                 struct folio_batch *fbatch; >> >>                 folio_get(folio); >> @@ -740,7 +740,8 @@ void folio_mark_lazyfree(struct folio *folio) >>  { >>         if (folio_test_lru(folio) && folio_test_anon(folio) && >>             folio_test_swapbacked(folio) && >> !folio_test_swapcache(folio) && >> -           !folio_test_unevictable(folio)) { >> +           !folio_test_unevictable(folio) && >> +           folio_test_clear_lru(folio)) { >>                 struct folio_batch *fbatch; >> >>                 folio_get(folio); > > With your changes, we will call folio_test_clear_lru(folio) firstly to > clear the LRU flag, and then call folio_get(folio) to pin the folio, > seems a little unreasonable. Normally, folio_get(folio) is called > firstly to pin the page, and then some other functions is called to > handle the folio. Right, if that really matters (not sure if it does) we could do if (folio_test_lru(folio) && ... folio_get(folio); if (!folio_test_clear_lru(folio)) { folio_put(folio) } else { struct folio_batch *fbatch; } } -- Cheers, David / dhildenb