Re: [PATCH V7 02/19] dax: Factor out dax_folio_reset_order() helper
From: Dave Jiang <dave.jiang@intel.com>
Date: 2026-02-18 23:04:10
Also in:
linux-cxl, linux-fsdevel, lkml, nvdimm
On 1/18/26 3:31 PM, John Groves wrote:
From: John Groves <John@Groves.net> Both fs/dax.c:dax_folio_put() and drivers/dax/fsdev.c: fsdev_clear_folio_state() (the latter coming in the next commit after this one) contain nearly identical code to reset a compound DAX folio back to order-0 pages. Factor this out into a shared helper function. The new dax_folio_reset_order() function: - Clears the folio's mapping and share count - Resets compound folio state via folio_reset_order() - Clears PageHead and compound_head for each sub-page - Restores the pgmap pointer for each resulting order-0 folio - Returns the original folio order (for callers that need to advance by that many pages) This simplifies fsdev_clear_folio_state() from ~50 lines to ~15 lines while maintaining the same functionality in both call sites. Suggested-by: Jonathan Cameron <jonathan.cameron@huawei.com> Signed-off-by: John Groves <john@groves.net>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
quoted hunk ↗ jump to hunk
--- fs/dax.c | 60 +++++++++++++++++++++++++++++++++++++++----------------- 1 file changed, 42 insertions(+), 18 deletions(-)diff --git a/fs/dax.c b/fs/dax.c index 289e6254aa30..7d7bbfb32c41 100644 --- a/fs/dax.c +++ b/fs/dax.c@@ -378,6 +378,45 @@ static void dax_folio_make_shared(struct folio *folio) folio->share = 1; } +/** + * dax_folio_reset_order - Reset a compound DAX folio to order-0 pages + * @folio: The folio to reset + * + * Splits a compound folio back into individual order-0 pages, + * clearing compound state and restoring pgmap pointers. + * + * Returns: the original folio order (0 if already order-0) + */ +int dax_folio_reset_order(struct folio *folio) +{ + struct dev_pagemap *pgmap = page_pgmap(&folio->page); + int order = folio_order(folio); + int i; + + folio->mapping = NULL; + folio->share = 0; + + if (!order) { + folio->pgmap = pgmap; + return 0; + } + + folio_reset_order(folio); + + for (i = 0; i < (1UL << order); i++) { + struct page *page = folio_page(folio, i); + struct folio *f = (struct folio *)page; + + ClearPageHead(page); + clear_compound_head(page); + f->mapping = NULL; + f->share = 0; + f->pgmap = pgmap; + } + + return order; +} + static inline unsigned long dax_folio_put(struct folio *folio) { unsigned long ref;@@ -391,28 +430,13 @@ static inline unsigned long dax_folio_put(struct folio *folio) if (ref) return ref; - folio->mapping = NULL; - order = folio_order(folio); - if (!order) - return 0; - folio_reset_order(folio); + order = dax_folio_reset_order(folio); + /* Debug check: verify refcounts are zero for all sub-folios */ for (i = 0; i < (1UL << order); i++) { - struct dev_pagemap *pgmap = page_pgmap(&folio->page); 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; - WARN_ON_ONCE(folio_ref_count(new_folio)); + WARN_ON_ONCE(folio_ref_count((struct folio *)page)); } return ref;