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Thu, 27 Jun 2024 11:33:30 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id AmAgEgpOfWYhPwAAD6G6ig (envelope-from ); Thu, 27 Jun 2024 11:33:30 +0000 Received: by quack3.suse.cz (Postfix, from userid 1000) id 988C8A08A2; Thu, 27 Jun 2024 13:33:28 +0200 (CEST) Date: Thu, 27 Jun 2024 13:33:28 +0200 From: Jan Kara To: Alistair Popple Cc: dan.j.williams@intel.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, david@redhat.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-mm@kvack.org, linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org, jhubbard@nvidia.com, hch@lst.de, david@fromorbit.com Subject: Re: [PATCH 06/13] mm/memory: Add dax_insert_pfn Message-ID: <20240627113328.ozqkzhloufrpsdcr@quack3> References: <50013c1ee52b5bb1213571bff66780568455f54c.1719386613.git-series.apopple@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <50013c1ee52b5bb1213571bff66780568455f54c.1719386613.git-series.apopple@nvidia.com> X-Rspamd-Action: no action X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 3A66340014 X-Stat-Signature: rkmjbp7g18kusamrgdhqs9joq36ywsts X-Rspam-User: X-HE-Tag: 1719488012-528944 X-HE-Meta: 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 hD5CkMIb 5TVFzN+lnt2Mf6bP+x5lmo4GOs59GUtNdXDE3etws8nMGlBB7f15vIDBULxBszMMVykdfs77O0WWkgmRpwigaDxz17q0K5pvkc7cxL105fea31N2OVdD44/kQ2iZjLyYTxqxLCTT7bHjXrXP4qO9rEismtXXP9GauFBlYclsfL+j35YCtrqlRJMHxahgIKtjR80jlpWPuBhUAukVwJMFk2cTHMmcZr4y5lst2Ddz+LSi/JDnfHqf16rSURsxPGngvDQQudORhJZThQkgKyOEgixX/J1u063HU5Gapl9GyxD8N6AiU/02S65oTDZZcEoHOoxPP2uWQlDb7pzba0nhwW2Ks42sO3VZUi+mdQD8KnmhDdGJkDNTKJC05aGBrpBId1kGAQ2LS9VMm2gA= 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 Thu 27-06-24 10:54:21, Alistair Popple wrote: > Currently to map a DAX page the DAX driver calls vmf_insert_pfn. This > creates a special devmap PTE entry for the pfn but does not take a > reference on the underlying struct page for the mapping. This is > because DAX page refcounts are treated specially, as indicated by the > presence of a devmap entry. > > To allow DAX page refcounts to be managed the same as normal page > refcounts introduce dax_insert_pfn. This will take a reference on the > underlying page much the same as vmf_insert_page, except it also > permits upgrading an existing mapping to be writable if > requested/possible. > > Signed-off-by: Alistair Popple Overall this looks good to me. Some comments below. > --- > include/linux/mm.h | 4 ++- > mm/memory.c | 79 ++++++++++++++++++++++++++++++++++++++++++----- > 2 files changed, 76 insertions(+), 7 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 9a5652c..b84368b 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1080,6 +1080,8 @@ int vma_is_stack_for_current(struct vm_area_struct *vma); > struct mmu_gather; > struct inode; > > +extern void prep_compound_page(struct page *page, unsigned int order); > + You don't seem to use this function in this patch? > diff --git a/mm/memory.c b/mm/memory.c > index ce48a05..4f26a1f 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -1989,14 +1989,42 @@ static int validate_page_before_insert(struct page *page) > } > > static int insert_page_into_pte_locked(struct vm_area_struct *vma, pte_t *pte, > - unsigned long addr, struct page *page, pgprot_t prot) > + unsigned long addr, struct page *page, pgprot_t prot, bool mkwrite) > { > struct folio *folio = page_folio(page); > + pte_t entry = ptep_get(pte); > > - if (!pte_none(ptep_get(pte))) > + if (!pte_none(entry)) { > + if (mkwrite) { > + /* > + * For read faults on private mappings the PFN passed > + * in may not match the PFN we have mapped if the > + * mapped PFN is a writeable COW page. In the mkwrite > + * case we are creating a writable PTE for a shared > + * mapping and we expect the PFNs to match. If they > + * don't match, we are likely racing with block > + * allocation and mapping invalidation so just skip the > + * update. > + */ > + if (pte_pfn(entry) != page_to_pfn(page)) { > + WARN_ON_ONCE(!is_zero_pfn(pte_pfn(entry))); > + return -EFAULT; > + } > + entry = maybe_mkwrite(entry, vma); > + entry = pte_mkyoung(entry); > + if (ptep_set_access_flags(vma, addr, pte, entry, 1)) > + update_mmu_cache(vma, addr, pte); > + return 0; > + } > return -EBUSY; If you do this like: if (!mkwrite) return -EBUSY; You can reduce indentation of the big block and also making the flow more obvious... > + } > + > /* Ok, finally just insert the thing.. */ > folio_get(folio); > + if (mkwrite) > + entry = maybe_mkwrite(mk_pte(page, prot), vma); > + else > + entry = mk_pte(page, prot); I'd prefer: entry = mk_pte(page, prot); if (mkwrite) entry = maybe_mkwrite(entry, vma); but I don't insist. Also insert_pfn() additionally has pte_mkyoung() and pte_mkdirty(). Why was it left out here? Honza -- Jan Kara SUSE Labs, CR