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b=r57v5qpDP1JpL+YD/QaJaQgZtR5duvUUh90CXCPBJWiBbbSdK1/4QS/jk4W5Fm8pb ybMjtmNodPUshgbu2mGVTo7i4SunYaneQLWeZX6F2Fy0SvXxmPSRBEwsnvR+LnBvbm eFl2TYr+EMQZBFfaQSC+mVmACiLlvxpSL93C8f703OsXLv6CiWXRypuzJwj2oOpfFl b4qFJAUKNQrV5pmJIR7ibXzpk4groEy0hej/wz07tzOiAbyW5PY9UR/FYCe9AZPKDb HYGVATtm1OkvfnIE60Pnd8OcFtCwG2t0XJTFh0ByY2C+hUcJUaEF3IOCKyrUqYAOFc pTDUCaouS+UDw== Message-ID: <9ec9edd1-0f4c-4da2-ae78-0e7b251a9e25@kernel.org> Date: Thu, 26 Mar 2026 10:18:09 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4] mm/userfaultfd: fix hugetlb fault mutex hash calculation To: jane.chu@oracle.com, Andrew Morton , Jianhui Zhou , Muchun Song , Oscar Salvador , Mike Rapoport Cc: Peter Xu , Andrea Arcangeli , Mike Kravetz , SeongJae Park , Hugh Dickins , Sidhartha Kumar , Jonas Zhou , linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, syzbot+f525fd79634858f478e7@syzkaller.appspotmail.com References: <20260306140332.171078-1-jianhuizzzzz@gmail.com> <20260310110526.335749-1-jianhuizzzzz@gmail.com> <12e822c4-a4f2-4447-80b9-2eec35a03188@oracle.com> <20260324170311.dc5b54fe0765f2e680e3cc90@linux-foundation.org> <1075f7a0-232f-4268-94b3-573d11c4203f@kernel.org> <67287b4a-7b93-4061-af4d-65e4a163c61c@oracle.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam12 X-Stat-Signature: qzbrzemnbc7yk8bhnaxuwjecyajjyf7u X-Rspamd-Queue-Id: 87EDA140002 X-Rspam-User: X-HE-Tag: 1774516699-437552 X-HE-Meta: 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 TOthc5T7 K1vmW3I9y0kWhYHgX6EGVpRESrmyrPOnZa+UoC0LuOLNKN66mdQ56S+jRwDcRottYTiyxo9dmkBUGw0mCBG4eqy9y6EftL5DD2sGsFlFX3g3AsTJRFifGuAI43rrdmnGGfvalb0Zf4BM0wBuc90SvC2G/wkVVdTatKJTAk7qjsk8Ui1wV8FD32z93GRxyPSUyZFr+TWR4g7qr6qgXQXtwgK1DWhmsM183YnKeendniQCeJBU/3BMR4Tin0OUorzaKkE/O6UN291G6yOOUx8n3eqex98gDne/fWLEc8T0fWCuyuOxpu1gn/7hUlX9dNFdXvT8iLi/u4Wioz4sKy2U5sDb2vNrGPbN+LrpqDEXOFDIw4IQ= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/26/26 00:46, jane.chu@oracle.com wrote: > Hi, David, > > On 3/25/2026 1:49 AM, David Hildenbrand (Arm) wrote: > [..] [...] >> >> But it raises the question: >> >> (1) should be convert all that to just operate on the ordinary index, >> such that we don't even need hugetlb_linear_page_index()? That would be >> an addon patch. >> > > Do you mean to convert all callers of hugetlb_linear_page_index() and > vma_hugepcache_offset() to use index and huge_page_order(h) ? > May I add, to improve readability, rename the huge-page-granularity > 'idx' to huge_idx or hidx ? What I meant is that we change all hugetlb code to use the ordinary idx. It's a bigger rework. For example, we'd be getting rid of filemap_lock_hugetlb_folio() completely and simply use filemap_lock_folio. As one example: @@ -657,10 +657,9 @@ static void hugetlbfs_zero_partial_page(struct hstate *h, loff_t start, loff_t end) { - pgoff_t idx = start >> huge_page_shift(h); struct folio *folio; - folio = filemap_lock_hugetlb_folio(h, mapping, idx); + folio = filemap_lock_folio(mapping, start >> PAGE_SHIFT); if (IS_ERR(folio)) return; Other parts are more tricky, as we have to make sure that we get an idx that points at the start of the folio. Likely such a conversion could be done incrementally. But it's a bit of work. We'd be getting rid of some more hugetlb special casing. An alternative is passing in an address into hugetlb_linear_page_index(), just letting it do the calculation itself (it can get the hstate from the mapping). > >> (2) Alternatively, could we replace all users of vma_hugecache_offset() >> by the much cleaner hugetlb_linear_page_index() ? >> > > The difference between the two helpers is hstate_vma() in the latter > that is about 5 pointer de-references, not sure of any performance > implication though.  hstate_vma() is really just hstate_file(vma->vm_file)-> hstate_inode(file_inode(f))->HUGETLBFS_SB(i->i_sb)->hstate; So some pointer chasing. hard to believe that this would matter in any of this code :) > At minimum, we could have >   hugetlb_linear_page_index(vma, addr) >   -> __hugetlb_linear_page_index(h, vma, addr) > basically renaming vma_hugecache_offset(). I would only do that if it's really required for performance. -- Cheers, David