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Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lance Yang , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Alistair Popple , Francois Dugast Subject: [PATCH v3 1/7] mm: Add folio_split_unref helper Date: Fri, 9 Jan 2026 09:54:21 +0100 Message-ID: <20260109085605.443316-2-francois.dugast@intel.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260109085605.443316-1-francois.dugast@intel.com> References: <20260109085605.443316-1-francois.dugast@intel.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 534AC140009 X-Stat-Signature: zcjbxgbpjo3cx9h3zrnb5gfy4fqeopm8 X-HE-Tag: 1767948995-207792 X-HE-Meta: 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 4bto52BE 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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 folio_split_unref helper which splits an unreferenced folio (refcount == 0) into individual pages. Intended to be called on special pages (e.g., device-private, DAX, etc.) when returning the folio to the free page pool. Cc: Balbir Singh Cc: Andrew Morton Cc: David Hildenbrand Cc: Lorenzo Stoakes Cc: Zi Yan Cc: Baolin Wang Cc: "Liam R. Howlett" Cc: Nico Pache Cc: Ryan Roberts Cc: Dev Jain Cc: Barry Song Cc: Lance Yang Cc: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org Suggested-by: Alistair Popple Signed-off-by: Matthew Brost Signed-off-by: Francois Dugast --- include/linux/huge_mm.h | 1 + mm/huge_memory.c | 39 +++++++++++++++++++++++++++++++++++++++ 2 files changed, 40 insertions(+) diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h index a4d9f964dfde..18cb9728d8f1 100644 --- a/include/linux/huge_mm.h +++ b/include/linux/huge_mm.h @@ -369,6 +369,7 @@ enum split_type { SPLIT_TYPE_NON_UNIFORM, }; +void folio_split_unref(struct folio *folio); int __split_huge_page_to_list_to_order(struct page *page, struct list_head *list, unsigned int new_order); int folio_split_unmapped(struct folio *folio, unsigned int new_order); diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 40cf59301c21..0eb9e6ad8639 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -3580,6 +3580,45 @@ static void __split_folio_to_order(struct folio *folio, int old_order, ClearPageCompound(&folio->page); } +/** + * folio_split_unref() - split an unreferenced folio (refcount == 0) + * @folio: the to-be-split folio + * + * Split an unreferenced folio (refcount == 0) into individual pages. + * Intended to be called on special pages (e.g., device-private, DAX, etc.) + * when returning the folio to the free page pool. + */ +void folio_split_unref(struct folio *folio) +{ + struct dev_pagemap *pgmap = page_pgmap(&folio->page); + int order, i; + + 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); + } +} +EXPORT_SYMBOL_GPL(folio_split_unref); + /** * __split_unmapped_folio() - splits an unmapped @folio to lower order folios in * two ways: uniform split or non-uniform split. -- 2.43.0