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[2003:d8:2f25:1e00:ce4c:be3:97b3:6587]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45b81a9e971sm278712005e9.18.2025.09.03.23.20.12 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 03 Sep 2025 23:20:12 -0700 (PDT) Message-ID: <8fbec487-b696-48ea-a449-411ec74ad378@redhat.com> Date: Thu, 4 Sep 2025 08:20:11 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] filemap: optimize order0 folio in filemap_map_pages To: Jinjiang Tu , willy@infradead.org, akpm@linux-foundation.org, linux-mm@kvack.org Cc: wangkefeng.wang@huawei.com References: <20250903084223.1653192-1-tujinjiang@huawei.com> <3c283054-b14e-4f36-966f-78cf3bc0f3af@redhat.com> <407a9aae-43b9-456b-b626-4eec55909dee@huawei.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 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <407a9aae-43b9-456b-b626-4eec55909dee@huawei.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: 3lhPxBjFNuVxnKoDoSgx73BYxq13raChZbEd7B1CTS4_1756966813 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: CC2C720006 X-Rspamd-Server: rspam04 X-Rspam-User: X-Stat-Signature: c1ru91385x73ofugs9q69t95hndmjux9 X-HE-Tag: 1756966818-614743 X-HE-Meta: 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 Ur0ybobC Yuv2tI2VMQrUj+It7I5CICeexJZtuxG7gGdbjaTTb7GMWom7OXyGZXmTUaAxj9eQfebkErgfB1Q9b8O9dwihOAqQPWg== 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 04.09.25 03:06, Jinjiang Tu wrote: > > 在 2025/9/4 9:05, Jinjiang Tu 写道: >> >> >> 在 2025/9/3 17:16, David Hildenbrand 写道: >>>> +++ b/mm/filemap.c >>>> @@ -3693,6 +3693,7 @@ static vm_fault_t >>>> filemap_map_folio_range(struct vm_fault *vmf, >>>>       } >>>>         vmf->pte = old_ptep; >>>> +    folio_put(folio); >>>>         return ret; >>>>   } >>>> @@ -3705,7 +3706,7 @@ static vm_fault_t >>>> filemap_map_order0_folio(struct vm_fault *vmf, >>>>       struct page *page = &folio->page; >>>>         if (PageHWPoison(page)) >>>> -        return ret; >>>> +        goto out; >>>>         /* See comment of filemap_map_folio_range() */ >>>>       if (!folio_test_workingset(folio)) >>>> @@ -3717,15 +3718,17 @@ static vm_fault_t >>>> filemap_map_order0_folio(struct vm_fault *vmf, >>>>        * the fault-around logic. >>>>        */ >>>>       if (!pte_none(ptep_get(vmf->pte))) >>>> -        return ret; >>>> +        goto out; >>>>         if (vmf->address == addr) >>>>           ret = VM_FAULT_NOPAGE; >>>>         set_pte_range(vmf, folio, page, 1, addr); >>>>       (*rss)++; >>>> -    folio_ref_inc(folio); >>>> +    return ret; >>>>   +out: >>>> +    folio_put(folio); >>> >>> We can use a folio_ref_dec() here >>> >>>     /* Locked folios cannot get truncated. */ >>>     folio_ref_dec(folio); >>> >>>>       return ret; >>>>   } >>>>   @@ -3785,7 +3788,6 @@ vm_fault_t filemap_map_pages(struct vm_fault >>>> *vmf, >>>>                       nr_pages, &rss, &mmap_miss); >>>>             folio_unlock(folio); >>>> -        folio_put(folio); >>>>       } while ((folio = next_uptodate_folio(&xas, mapping, >>>> end_pgoff)) != NULL); >>>>       add_mm_counter(vma->vm_mm, folio_type, rss); >>>>       pte_unmap_unlock(vmf->pte, vmf->ptl); >>> >>> >>> I think we can optimize filemap_map_folio_range() as well: >>> >>> diff --git a/mm/filemap.c b/mm/filemap.c >>> index b101405b770ae..d1fcddc72c5f6 100644 >>> --- a/mm/filemap.c >>> +++ b/mm/filemap.c >>> @@ -3646,6 +3646,7 @@ static vm_fault_t >>> filemap_map_folio_range(struct vm_fault *vmf, >>>                         unsigned long addr, unsigned int nr_pages, >>>                         unsigned long *rss, unsigned short *mmap_miss) >>>  { >>> +       bool ref_from_caller = true; >>>         vm_fault_t ret = 0; >>>         struct page *page = folio_page(folio, start); >>>         unsigned int count = 0; >>> @@ -3679,7 +3680,9 @@ static vm_fault_t >>> filemap_map_folio_range(struct vm_fault *vmf, >>>                 if (count) { >>>                         set_pte_range(vmf, folio, page, count, addr); >>>                         *rss += count; >>> -                       folio_ref_add(folio, count); >>> +                       if (count - ref_from_caller) >>> +                               folio_ref_add(folio, count - >>> ref_from_caller); >>> +                       ref_from_caller = false; >>>                         if (in_range(vmf->address, addr, count * >>> PAGE_SIZE)) >>>                                 ret = VM_FAULT_NOPAGE; >>>                 } >>> @@ -3694,13 +3697,19 @@ static vm_fault_t >>> filemap_map_folio_range(struct vm_fault *vmf, >>>         if (count) { >>>                 set_pte_range(vmf, folio, page, count, addr); >>>                 *rss += count; >>> -               folio_ref_add(folio, count); >>> +               if (count - ref_from_caller) >>> +                       folio_ref_add(folio, count - ref_from_caller); >>> +               ref_from_caller = false; >>>                 if (in_range(vmf->address, addr, count * PAGE_SIZE)) >>>                         ret = VM_FAULT_NOPAGE; >>>         } >>> >>>         vmf->pte = old_ptep; >>> >>> +       if (ref_from_caller) >>> +               /* Locked folios cannot get truncated. */ >>> +               folio_ref_dec(folio); >>> + >>>         return ret; >>>  } >>> >>> >>> It would save at least a folio_ref_dec(), and in corner cases (only >>> map a single page) >>> also a folio_ref_add(). >>> >> Maybe We can first count the refcount to add, and only call folio_ref_{add, sub} once before return I'm not a fan of that, because I'm planning on moving the folio_ref_add() before the set_pte_range() so we can minimize the number of false positives with our folio_ref_count() != folio_expected_ref_count() checks, and I can sanity check when adjusting the mapcount that it is always >= refcount. -- Cheers David / dhildenb