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[2003:cb:c73d:de00:7cf7:9482:e5dc:6ad0]) by smtp.gmail.com with ESMTPSA id r2-20020a0560001b8200b00336f8b2f60fsm4732259wru.8.2024.01.10.04.00.13 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 10 Jan 2024 04:00:14 -0800 (PST) Message-ID: <2c930548-c290-476a-a8e4-3643d75df995@redhat.com> Date: Wed, 10 Jan 2024 13:00:12 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] support tmpfs hugepage PMD is not split when COW To: Chen Haixiang , linux-mm@kvack.org, akpm@linux-foundation.org, hughd@google.com Cc: louhongxiang@huawei.com, wangbin224@huawei.com, liuyuntao10@huawei.com References: <20240110092028.1777-1-chenhaixiang3@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 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: <20240110092028.1777-1-chenhaixiang3@huawei.com> X-Mimecast-Spam-Score: 0 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: rspam09 X-Rspamd-Queue-Id: E187F40028 X-Stat-Signature: 6yi7165h1839kqdokgooirki4whu96tb X-Rspam-User: X-HE-Tag: 1704888018-995566 X-HE-Meta: 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 9Kv4O6Va 2yraRU3uPyTLzlAAsuGjJrn7VmD4RhLZLnIzFiuxUtN5kWs+VRs3WpBkjvTIv27aRQuI+oXexiFYwF6G6+hgfhmUVZGaQvO6QF3l7iMXME0EMPlZ4p3Tbn4ueKGLbmOzfGeaqod6B57ssFbz2es5oFj2sDzw66ixgBXx6H0/QBZUwE//d9DgrmA110bannK2xqOz4HKwDIvcmSLiwHNgAJVOrslHmvScFxKWoCXj1hU3O8DJE9YrbUzdoKHjxNWt3Pa/sI+2RIsUBehG8NO5XFx7gY8z7MlrWWazTfqKE98DIAkALw1gtPeqQkbiQfs5+tw1INp86ZoKTafWck8q87n7p2MUb7AMGKc7JR25meUuyJZerRnISOcT9F0virT4bNjZHxzqOgUt4hIJNdIza26PYNFX6PLdcERNFPAuwRJt3WArB+CiuCaC1dPQbdOoBWsKv 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 10.01.24 10:20, Chen Haixiang wrote: > Transparent hugepages in tmpfs can enhance TLB efficiency by reducing > TLB misses. However, during Copy-On-Write (COW) memory faults, these > hugepages may be split. In some scenarios, preventing this splitting > is desirable. We might introduce a shmem_huge_fault to inhibit this > behavior, along with a mount parameter to enable or disable this function. > I'm confused, can you describe the problem a bit better, because ... > Signed-off-by: Chen Haixiang > --- [...] > > +static vm_fault_t shmem_huge_fault(struct vm_fault *vmf, pmd_t orig_pmd) > +{ > + vm_fault_t ret = VM_FAULT_FALLBACK; > + unsigned long haddr = vmf->address & HPAGE_PMD_MASK; > + struct folio *old_folio, *new_folio; > + pmd_t entry; > + int gfp_flags = GFP_HIGHUSER_MOVABLE | __GFP_COMP; > + struct vm_area_struct *vma = vmf->vma; > + struct shmem_sb_info *sbinfo = NULL; > + struct inode *inode = file_inode(vma->vm_file); > + struct shmem_inode_info *info = SHMEM_I(inode); > + > + sbinfo = SHMEM_SB(info->vfs_inode.i_sb); > + > + if (sbinfo->no_split == 0) > + return VM_FAULT_FALLBACK; > + > + /* ShmemPmdMapped in tmpfs will not split huge pmd */ > + if (!(vmf->flags & FAULT_FLAG_WRITE) > + || (vma->vm_flags & VM_SHARED)) > + return VM_FAULT_FALLBACK; We do have a private (COW) mapping at this point, and > + > + new_folio = vma_alloc_folio(gfp_flags, HPAGE_PMD_ORDER, > + vmf->vma, haddr, true); > + if (!new_folio) > + ret = VM_FAULT_FALLBACK; > + > + vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd); > + if (pmd_none(*vmf->pmd)) { > + ret = VM_FAULT_FALLBACK; > + goto out; > + } > + if (!pmd_same(*vmf->pmd, orig_pmd)) { > + ret = 0; > + goto out; > + } > + > + if (!new_folio) { > + count_vm_event(THP_FAULT_FALLBACK); > + ret = VM_FAULT_FALLBACK; > + goto out; > + } > + old_folio = page_folio(pmd_page(*vmf->pmd)); > + page_remove_rmap(&old_folio->page, vma, true); > + pmdp_huge_clear_flush(vma, haddr, vmf->pmd); > + > + __folio_set_locked(new_folio); > + __folio_set_swapbacked(new_folio); > + __folio_mark_uptodate(new_folio); We allocate a fresh folio here and > + > + flush_icache_pages(vma, &new_folio->page, HPAGE_PMD_NR); > + entry = mk_huge_pmd(&new_folio->page, vma->vm_page_prot); > + entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma); > + > + page_add_file_rmap(&new_folio->page, vma, true); it is not an anonymous one? ... but your are making it writable? In a private mapping? > + set_pmd_at(vma->vm_mm, haddr, vmf->pmd, entry); > + update_mmu_cache_pmd(vma, haddr, vmf->pmd); > + count_vm_event(THP_FILE_MAPPED); And still acoount it as a file folio? But never add it so some pagecache structure? I'm probably missing something, or something is completely wrong here. -- Cheers, David / dhildenb