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[2003:cb:c739:900:900f:3c9e:2f7b:5d0a]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38f258b4118sm13425148f8f.18.2025.02.17.11.58.39 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 17 Feb 2025 11:58:43 -0800 (PST) Message-ID: <519c6ef7-ca56-4aac-8e43-f75b17353d66@redhat.com> Date: Mon, 17 Feb 2025 20:58:38 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v7 16/20] huge_memory: Add vmf_insert_folio_pmd() To: Alistair Popple Cc: akpm@linux-foundation.org, dan.j.williams@intel.com, linux-mm@kvack.org, Alison Schofield , lina@asahilina.net, zhang.lyra@gmail.com, gerald.schaefer@linux.ibm.com, vishal.l.verma@intel.com, dave.jiang@intel.com, logang@deltatee.com, bhelgaas@google.com, jack@suse.cz, jgg@ziepe.ca, catalin.marinas@arm.com, will@kernel.org, mpe@ellerman.id.au, npiggin@gmail.com, dave.hansen@linux.intel.com, ira.weiny@intel.com, willy@infradead.org, djwong@kernel.org, tytso@mit.edu, linmiaohe@huawei.com, peterx@redhat.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, nvdimm@lists.linux.dev, linux-cxl@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org, jhubbard@nvidia.com, hch@lst.de, david@fromorbit.com, chenhuacai@kernel.org, kernel@xen0n.name, loongarch@lists.linux.dev References: <9f10e88441f3cb26eff6be0c9ef5997844c8c24e.1738709036.git-series.apopple@nvidia.com> <6mmjoe27y63cfe5cycqje63gehgumod3bp7zzgvpz7qehgfuv4@uomvqgizba2m> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 9769914000A X-Stat-Signature: 4uu47dz8jgjdm61h7iu7xe943uezcfrs X-HE-Tag: 1739822330-453653 X-HE-Meta: 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 RohEMHRF 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 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 17.02.25 05:29, Alistair Popple wrote: > On Mon, Feb 10, 2025 at 07:45:09PM +0100, David Hildenbrand wrote: >> On 04.02.25 23:48, Alistair Popple wrote: >>> Currently DAX folio/page reference counts are managed differently to normal >>> pages. To allow these to be managed the same as normal pages introduce >>> vmf_insert_folio_pmd. This will map the entire PMD-sized folio and take >>> references as it would for a normally mapped page. >>> >>> This is distinct from the current mechanism, vmf_insert_pfn_pmd, which >>> simply inserts a special devmap PMD entry into the page table without >>> holding a reference to the page for the mapping. >>> >>> It is not currently useful to implement a more generic vmf_insert_folio() >>> which selects the correct behaviour based on folio_order(). This is because >>> PTE faults require only a subpage of the folio to be PTE mapped rather than >>> the entire folio. It would be possible to add this context somewhere but >>> callers already need to handle PTE faults and PMD faults separately so a >>> more generic function is not useful. >>> >>> Signed-off-by: Alistair Popple >> >> Nit: patch subject ;) >> >>> >>> --- >>> >>> Changes for v7: >>> >>> - Fix bad pgtable handling for PPC64 (Thanks Dan and Dave) >> >> Is it? ;) insert_pfn_pmd() still doesn't consume a "pgtable_t *" >> >> But maybe I am missing something ... > > At a high-level all I'm trying to do (perhaps badly) is pull the ptl locking one > level up the callstack. > > As far as I can tell the pgtable is consumed here: > > static int insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr, > pmd_t *pmd, pfn_t pfn, pgprot_t prot, bool write, > pgtable_t pgtable) > > [...] > > if (pgtable) { > pgtable_trans_huge_deposit(mm, pmd, pgtable); > mm_inc_nr_ptes(mm); > pgtable = NULL; > } > > [...] > > return 0; > > Now I can see I failed to clean up the useless pgtable = NULL asignment, which > is confusing because I'm not trying to look at pgtable in the caller (ie. > vmf_insert_pfn_pmd()/vmf_insert_folio_pmd()) to determine if it needs freeing. > So I will remove this assignment. Ahhh, yes, the "pgtable = NULL" confused me, so I was looking for a "pgtable_t *pgtable" being passed instead, that we could manipulate. > > Instead callers just look at the return code from insert_pfn_pmd() - if there > was an error pgtable_trans_huge_deposit(pgtable) wasn't called and if the caller > passed a pgtable it should be freed. Otherwise if insert_pfn_pmd() succeeded > then callers can assume the pgtable was consumed by pgtable_trans_huge_deposit() > and therefore should not be freed. > > Hopefully that all makes sense, but maybe I've missed something obvious too... Yes, you assume that if insert_pfn_pmd() succeeds, the table was consumed, otherwise it must be freed. Thanks! Acked-by: David Hildenbrand -- Cheers, David / dhildenb