From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D26383C1F for ; Tue, 18 Feb 2025 04:47:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739854071; cv=none; b=N/Tc8Vw8IrQVVOP1lwlZ0yLYxPgidb/s+M88hffvk4DFyYo3P3UbQrtJJX2IQegFV/qFqdy65x5CyFD/5WzUPZ9P8Gr4psbrnhN7+lOid/F7ehjaSpvLSxt78bFbi456POSN/uVVB8jTfrQRZimCXoOklHGYjLDMGFhDND5d8Z8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739854071; c=relaxed/simple; bh=FnEN0wlOEHFbv8QQ2A1Dr1kdEK3/gxomwdcAIwt1NDk=; h=Date:To:From:Subject:Message-Id; b=JbfFtLmUeJTEPbPjbrQlGPLAiseiLPfnZDoqZkOgTj4WITNwgxj3j7W6tInBvdSgnRyIlqhUsZaFQHUHuxDge8GJ4MghszXxvH1LfvUr0+psD49VR0yA7ZKFm7C2viqDJZ1lI3SUqPiXCAAoJqQSiWPocwWhDEDu0h6hPssMD6w= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=bnab2rGG; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="bnab2rGG" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 30CD0C4CEE2; Tue, 18 Feb 2025 04:47:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1739854071; bh=FnEN0wlOEHFbv8QQ2A1Dr1kdEK3/gxomwdcAIwt1NDk=; h=Date:To:From:Subject:From; b=bnab2rGGpdmdrFpbsEutvXkMtlg7Nbk+8fymoKEouZBw66k8zm/HEhOfj2oChAsGF sftAHWbWxtZ7rjYn2UKXCy9qfE8fNtO724ro8wS7q+yzQHXjgW/zYLdz4uEVdTNT1S ksYNbCv9Vb79+BmNS9/ay86cpjl3snZ2VNYmQHi0= Date: Mon, 17 Feb 2025 20:47:50 -0800 To: mm-commits@vger.kernel.org,zhang.lyra@gmail.com,willy@infradead.org,will@kernel.org,vishal.l.verma@intel.com,vgoyal@redhat.com,tytso@mit.edu,svens@linux.ibm.com,peterx@redhat.com,npiggin@gmail.com,mpe@ellerman.id.au,logang@deltatee.com,linmiaohe@huawei.com,lina@asahilina.net,kernel@xen0n.name,jhubbard@nvidia.com,jgg@ziepe.ca,jgg@nvidia.com,jack@suse.cz,ira.weiny@intel.com,hch@lst.de,hca@linux.ibm.com,gor@linux.ibm.com,gerald.schaefer@linux.ibm.com,djwong@kernel.org,david@redhat.com,david@fromorbit.com,dave.jiang@intel.com,dave.hansen@linux.intel.com,dan.j.williams@intel.com,chenhuacai@kernel.org,catalin.marinas@arm.com,borntraeger@linux.ibm.com,bhelgaas@google.com,balbirs@nvidia.com,alison.schofield@intel.com,agordeev@linux.ibm.com,apopple@nvidia.com,akpm@linux-foundation.org From: Andrew Morton Subject: + fs-dax-remove-page_mapping_dax_shared-mapping-flag.patch added to mm-unstable branch Message-Id: <20250218044751.30CD0C4CEE2@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: fs/dax: remove PAGE_MAPPING_DAX_SHARED mapping flag has been added to the -mm mm-unstable branch. Its filename is fs-dax-remove-page_mapping_dax_shared-mapping-flag.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/fs-dax-remove-page_mapping_dax_shared-mapping-flag.patch This patch will later appear in the mm-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days ------------------------------------------------------ From: Alistair Popple Subject: fs/dax: remove PAGE_MAPPING_DAX_SHARED mapping flag Date: Tue, 18 Feb 2025 14:55:24 +1100 The page ->mapping pointer can have magic values like PAGE_MAPPING_DAX_SHARED and PAGE_MAPPING_ANON for page owner specific usage. Currently PAGE_MAPPING_DAX_SHARED and PAGE_MAPPING_ANON alias to the same value. This isn't a problem because FS DAX pages are never seen by the anonymous mapping code and vice versa. However a future change will make FS DAX pages more like normal pages, so folio_test_anon() must not return true for a FS DAX page. We could explicitly test for a FS DAX page in folio_test_anon(), etc. however the PAGE_MAPPING_DAX_SHARED flag isn't actually needed. Instead we can use the page->mapping field to implicitly track the first mapping of a page. If page->mapping is non-NULL it implies the page is associated with a single mapping at page->index. If the page is associated with a second mapping clear page->mapping and set page->share to 1. This is possible because a shared mapping implies the file-system implements dax_holder_operations which makes the ->mapping and ->index, which is a union with ->share, unused. The page is considered shared when page->mapping == NULL and page->share > 0 or page->mapping != NULL, implying it is present in at least one address space. This also makes it easier for a future change to detect when a page is first mapped into an address space which requires special handling. Link: https://lkml.kernel.org/r/c22f699202db0acee2f7039eb026e68261ce42d6.1739850794.git-series.apopple@nvidia.com Signed-off-by: Alistair Popple Tested-by: Alison Schofield Cc: Alexander Gordeev Cc: Asahi Lina Cc: Balbir Singh Cc: Bjorn Helgaas Cc: Catalin Marinas Cc: Christian Borntraeger Cc: Christoph Hellwig Cc: Chunyan Zhang Cc: Dan Wiliams Cc: "Darrick J. Wong" Cc: Dave Chinner Cc: Dave Hansen Cc: Dave Jiang Cc: David Hildenbrand Cc: Gerald Schaefer Cc: Heiko Carstens Cc: Huacai Chen Cc: Ira Weiny Cc: Jan Kara Cc: Jason Gunthorpe Cc: Jason Gunthorpe Cc: John Hubbard Cc: Logan Gunthorpe Cc: Matthew Wilcox Cc: Miaohe Lin Cc: Michael Ellerman Cc: Nicholas Piggin Cc: Peter Xu Cc: Sven Schnelle Cc: Ted Ts'o Cc: Vasily Gorbik Cc: Vishal Verma Cc: Vivek Goyal Cc: WANG Xuerui Cc: Will Deacon Signed-off-by: Andrew Morton --- fs/dax.c | 55 +++++++++++++++++++++-------------- include/linux/page-flags.h | 6 --- 2 files changed, 33 insertions(+), 28 deletions(-) --- a/fs/dax.c~fs-dax-remove-page_mapping_dax_shared-mapping-flag +++ a/fs/dax.c @@ -351,27 +351,40 @@ static unsigned long dax_end_pfn(void *e for (pfn = dax_to_pfn(entry); \ pfn < dax_end_pfn(entry); pfn++) +/* + * A DAX folio is considered shared if it has no mapping set and ->share (which + * shares the ->index field) is non-zero. Note this may return false even if the + * page is shared between multiple files but has not yet actually been mapped + * into multiple address spaces. + */ static inline bool dax_folio_is_shared(struct folio *folio) { - return folio->mapping == PAGE_MAPPING_DAX_SHARED; + return !folio->mapping && folio->page.share; } /* - * Set the folio->mapping with PAGE_MAPPING_DAX_SHARED flag, increase the - * refcount. + * When it is called by dax_insert_entry(), the shared flag will indicate + * whether this entry is shared by multiple files. If the page has not + * previously been associated with any mappings the ->mapping and ->index + * fields will be set. If it has already been associated with a mapping + * the mapping will be cleared and the share count set. It's then up to + * reverse map users like memory_failure() to call back into the filesystem to + * recover ->mapping and ->index information. For example by implementing + * dax_holder_operations. */ -static inline void dax_folio_share_get(struct folio *folio) +static void dax_folio_make_shared(struct folio *folio) { - if (folio->mapping != PAGE_MAPPING_DAX_SHARED) { - /* - * Reset the index if the page was already mapped - * regularly before. - */ - if (folio->mapping) - folio->page.share = 1; - folio->mapping = PAGE_MAPPING_DAX_SHARED; - } - folio->page.share++; + /* + * folio is not currently shared so mark it as shared by clearing + * folio->mapping. + */ + folio->mapping = NULL; + + /* + * folio has previously been mapped into one address space so set the + * share count. + */ + folio->page.share = 1; } static inline unsigned long dax_folio_share_put(struct folio *folio) @@ -379,12 +392,6 @@ static inline unsigned long dax_folio_sh return --folio->page.share; } -/* - * When it is called in dax_insert_entry(), the shared flag will indicate - * that whether this entry is shared by multiple files. If so, set - * the folio->mapping PAGE_MAPPING_DAX_SHARED, and use page->share - * as refcount. - */ static void dax_associate_entry(void *entry, struct address_space *mapping, struct vm_area_struct *vma, unsigned long address, bool shared) { @@ -398,8 +405,12 @@ static void dax_associate_entry(void *en for_each_mapped_pfn(entry, pfn) { struct folio *folio = pfn_folio(pfn); - if (shared) { - dax_folio_share_get(folio); + if (shared && (folio->mapping || folio->page.share)) { + if (folio->mapping) + dax_folio_make_shared(folio); + + WARN_ON_ONCE(!folio->page.share); + folio->page.share++; } else { WARN_ON_ONCE(folio->mapping); folio->mapping = mapping; --- a/include/linux/page-flags.h~fs-dax-remove-page_mapping_dax_shared-mapping-flag +++ a/include/linux/page-flags.h @@ -710,12 +710,6 @@ PAGEFLAG_FALSE(VmemmapSelfHosted, vmemma #define PAGE_MAPPING_KSM (PAGE_MAPPING_ANON | PAGE_MAPPING_MOVABLE) #define PAGE_MAPPING_FLAGS (PAGE_MAPPING_ANON | PAGE_MAPPING_MOVABLE) -/* - * Different with flags above, this flag is used only for fsdax mode. It - * indicates that this page->mapping is now under reflink case. - */ -#define PAGE_MAPPING_DAX_SHARED ((void *)0x1) - static __always_inline bool folio_mapping_flags(const struct folio *folio) { return ((unsigned long)folio->mapping & PAGE_MAPPING_FLAGS) != 0; _ Patches currently in -mm which might be from apopple@nvidia.com are fuse-fix-dax-truncate-punch_hole-fault-path.patch fs-dax-return-unmapped-busy-pages-from-dax_layout_busy_page_range.patch fs-dax-dont-skip-locked-entries-when-scanning-entries.patch fs-dax-refactor-wait-for-dax-idle-page.patch fs-dax-create-a-common-implementation-to-break-dax-layouts.patch fs-dax-always-remove-dax-page-cache-entries-when-breaking-layouts.patch fs-dax-ensure-all-pages-are-idle-prior-to-filesystem-unmount.patch fs-dax-remove-page_mapping_dax_shared-mapping-flag.patch mm-gup-remove-redundant-check-for-pci-p2pdma-page.patch mm-mm_init-move-p2pdma-page-refcount-initialisation-to-p2pdma.patch mm-allow-compound-zone-device-pages.patch mm-memory-enhance-insert_page_into_pte_locked-to-create-writable-mappings.patch mm-memory-add-vmf_insert_page_mkwrite.patch mm-rmap-add-support-for-pud-sized-mappings-to-rmap.patch mm-huge_memory-add-vmf_insert_folio_pud.patch mm-huge_memory-add-vmf_insert_folio_pmd.patch mm-gup-dont-allow-foll_longterm-pinning-of-fs-dax-pages.patch fs-dax-properly-refcount-fs-dax-pages.patch device-dax-properly-refcount-device-dax-pages-when-mapping.patch