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Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Alistair Popple , linux-mm@kvack.org, linux-cxl@vger.kernel.org, linux-kernel@vger.kernel.org, Francois Dugast Subject: [PATCH v4 2/7] mm/zone_device: Add free_zone_device_folio_prepare() helper Date: Sun, 11 Jan 2026 21:55:41 +0100 Message-ID: <20260111205820.830410-3-francois.dugast@intel.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260111205820.830410-1-francois.dugast@intel.com> References: <20260111205820.830410-1-francois.dugast@intel.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: tzmqd4k7k13ymnboffbjewiwytsxcjtp X-Rspamd-Queue-Id: 4FC63140008 X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1768165156-210850 X-HE-Meta: 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 BNRVSrRx 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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: From: Matthew Brost Add free_zone_device_folio_prepare(), a helper that restores large ZONE_DEVICE folios to a sane, initial state before freeing them. Compound ZONE_DEVICE folios overwrite per-page state (e.g. pgmap and compound metadata). Before returning such pages to the device pgmap allocator, each constituent page must be reset to a standalone ZONE_DEVICE folio with a valid pgmap and no compound state. Use this helper prior to folio_free() for device-private and device-coherent folios to ensure consistent device page state for subsequent allocations. Fixes: d245f9b4ab80 ("mm/zone_device: support large zone device private folios") Cc: Zi Yan Cc: David Hildenbrand Cc: Oscar Salvador Cc: Andrew Morton Cc: Balbir Singh Cc: Lorenzo Stoakes Cc: Liam R. Howlett Cc: Vlastimil Babka Cc: Mike Rapoport Cc: Suren Baghdasaryan Cc: Michal Hocko Cc: Alistair Popple Cc: linux-mm@kvack.org Cc: linux-cxl@vger.kernel.org Cc: linux-kernel@vger.kernel.org Suggested-by: Alistair Popple Signed-off-by: Matthew Brost Signed-off-by: Francois Dugast --- include/linux/memremap.h | 1 + mm/memremap.c | 55 ++++++++++++++++++++++++++++++++++++++++ 2 files changed, 56 insertions(+) diff --git a/include/linux/memremap.h b/include/linux/memremap.h index 97fcffeb1c1e..88e1d4707296 100644 --- a/include/linux/memremap.h +++ b/include/linux/memremap.h @@ -230,6 +230,7 @@ static inline bool is_fsdax_page(const struct page *page) #ifdef CONFIG_ZONE_DEVICE void zone_device_page_init(struct page *page, unsigned int order); +void free_zone_device_folio_prepare(struct folio *folio); void *memremap_pages(struct dev_pagemap *pgmap, int nid); void memunmap_pages(struct dev_pagemap *pgmap); void *devm_memremap_pages(struct device *dev, struct dev_pagemap *pgmap); diff --git a/mm/memremap.c b/mm/memremap.c index 39dc4bd190d0..375a61e18858 100644 --- a/mm/memremap.c +++ b/mm/memremap.c @@ -413,6 +413,60 @@ struct dev_pagemap *get_dev_pagemap(unsigned long pfn) } EXPORT_SYMBOL_GPL(get_dev_pagemap); +/** + * free_zone_device_folio_prepare() - Prepare a ZONE_DEVICE folio for freeing. + * @folio: ZONE_DEVICE folio to prepare for release. + * + * ZONE_DEVICE pages/folios (e.g., device-private memory or fsdax-backed pages) + * can be compound. When freeing a compound ZONE_DEVICE folio, the tail pages + * must be restored to a sane ZONE_DEVICE state before they are released. + * + * This helper: + * - Clears @folio->mapping and, for compound folios, clears each page's + * compound-head state (ClearPageHead()/clear_compound_head()). + * - Resets the compound order metadata (folio_reset_order()) and then + * initializes each constituent page as a standalone ZONE_DEVICE folio: + * * clears ->mapping + * * restores ->pgmap (prep_compound_page() overwrites it) + * * clears ->share (only relevant for fsdax; unused for device-private) + * + * If @folio is order-0, only the mapping is cleared and no further work is + * required. + */ +void free_zone_device_folio_prepare(struct folio *folio) +{ + struct dev_pagemap *pgmap = page_pgmap(&folio->page); + int order, i; + + VM_WARN_ON_FOLIO(!folio_is_zone_device(folio), folio); + + folio->mapping = NULL; + order = folio_order(folio); + if (!order) + return; + + folio_reset_order(folio); + + for (i = 0; i < (1UL << order); i++) { + struct page *page = folio_page(folio, i); + struct folio *new_folio = (struct folio *)page; + + ClearPageHead(page); + clear_compound_head(page); + + new_folio->mapping = NULL; + /* + * Reset pgmap which was over-written by + * prep_compound_page(). + */ + new_folio->pgmap = pgmap; + new_folio->share = 0; /* fsdax only, unused for device private */ + VM_WARN_ON_FOLIO(folio_ref_count(new_folio), new_folio); + VM_WARN_ON_FOLIO(!folio_is_zone_device(new_folio), new_folio); + } +} +EXPORT_SYMBOL_GPL(free_zone_device_folio_prepare); + void free_zone_device_folio(struct folio *folio) { struct dev_pagemap *pgmap = folio->pgmap; @@ -454,6 +508,7 @@ void free_zone_device_folio(struct folio *folio) case MEMORY_DEVICE_COHERENT: if (WARN_ON_ONCE(!pgmap->ops || !pgmap->ops->folio_free)) break; + free_zone_device_folio_prepare(folio); pgmap->ops->folio_free(folio, order); percpu_ref_put_many(&folio->pgmap->ref, nr); break; -- 2.43.0