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b=TfLp61l4kZy0MZZX/i8lmL2bWboeNoeRN0JRhVX5J/9odaQrXnMiGGsl/ix0dOaLE8VSEDywKfBWpsQyMJTjuIrH3p4cxJH8rZUV3sgdsnSmHHoE56ufBmFLkh0ioUG2nZG04KWxXQLAAIbg0ICo/sG7XD5aJfq9LL/1JSdhDC0= Received: from 30.0.158.159(mailfrom:baolin.wang@linux.alibaba.com fp:SMTPD_---0WZqoxFK_1746621414 cluster:ay36) by smtp.aliyun-inc.com; Wed, 07 May 2025 20:36:55 +0800 Message-ID: <88060373-d0b8-404a-b53b-9b5a54f5ba6f@linux.alibaba.com> Date: Wed, 7 May 2025 20:36:54 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/2] mm: convert do_set_pmd() to take a folio To: Matthew Wilcox Cc: akpm@linux-foundation.org, david@redhat.com, hannes@cmpxchg.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, ziy@nvidia.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <8e33c8a65b46170dfd8ba6715d2115856a55b8f6.1746609191.git.baolin.wang@linux.alibaba.com> From: Baolin Wang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 1DF7C1C0007 X-Rspam-User: X-Rspamd-Server: rspam07 X-Stat-Signature: q8wbaqczr367wd3tte9ftbgf4ka6zzn7 X-HE-Tag: 1746621419-6015 X-HE-Meta: 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 hq9mmOmS lqlGs5qsM98A5+3UHMaZ+tHnTJFqoVrYBIjytc0hwKdVX3zXVHsW8cCG3vjRiJ/MTVckmnSBfieZnU4JT0MWwXIfK0o1ZhiQk/7IGrCmIR0XWAiT5me7JOBN9DPF0p+E2venPNHACuMzE3UhhaKiPxhGuL5LfyR7NKd2p6mfT39c5TapQhnlSomd77SjqsX1HpewDTBuufCUONqnC7x3G2c/gtJmAvU2RR41KaOZVZalo+oLwBDUiu6a97BuXvbuKv3n6DbPAki3PfUU1lR58G/KhnCbcaC4LUlC6FCPaj0J8Kvu12GidMTDknoXwJViN4g3ssoTsDCtuQ1k= 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 2025/5/7 20:10, Matthew Wilcox wrote: > On Wed, May 07, 2025 at 05:26:13PM +0800, Baolin Wang wrote: >> In do_set_pmd(), we always use the folio->page to build PMD mappings for >> the entire folio. Since all callers of do_set_pmd() already hold a stable >> folio, converting do_set_pmd() to take a folio is safe and more straightforward. > > What testing did you do of this? I did mm selftests, tmpfs/xfs PMD-sized mmap() tests. > >> -vm_fault_t do_set_pmd(struct vm_fault *vmf, struct page *page) >> +vm_fault_t do_set_pmd(struct vm_fault *vmf, struct folio *folio) >> { >> - struct folio *folio = page_folio(page); >> struct vm_area_struct *vma = vmf->vma; >> bool write = vmf->flags & FAULT_FLAG_WRITE; >> unsigned long haddr = vmf->address & HPAGE_PMD_MASK; >> pmd_t entry; >> vm_fault_t ret = VM_FAULT_FALLBACK; >> + struct page *page; > > Because I see nowhere in this patch that you initialise 'page'. Please look at the following code in do_set_pmd(), and the 'page' will be initialized before using. if (thp_disabled_by_hw() || vma_thp_disabled(vma, vma->vm_flags)) return ret; if (!thp_vma_suitable_order(vma, haddr, PMD_ORDER)) return ret; if (folio_order(folio) != HPAGE_PMD_ORDER) return ret; page = &folio->page; > And that's really the important part. You seem to be assuming that a > folio will never be larger than PMD size, and I'm not comfortable with No, I have no this assumption. But do_set_pmd() is used to establish PMD mappings for the PMD-sized folios, and we already have PMD-sized checks to validate the folio size: if (!thp_vma_suitable_order(vma, haddr, PMD_ORDER)) return ret; if (folio_order(folio) != HPAGE_PMD_ORDER) return ret; > that assumption. It's a limitation I put in place a few years ago so we > didn't have to find and fix all those assumptions immediately, but I > imagine that some day we'll want to have larger folios. > > So unless you can derive _which_ page in the folio we want to map from IMO, for PMD mapping of a PMD-sized folio, we do not need to know _which_ page in the folio we want to map, because we'll always map the entire PMD-sized folio. > the vmf, NACK this patch.