From: Ira Weiny <[email protected]> release_pages() is an optimized version of a loop around put_page(). Unfortunately for devmap pages the logic is not entirely correct in release_pages(). This is because device pages can be more than type MEMORY_DEVICE_PUBLIC. There are in fact 4 types, private, public, FS DAX, and PCI P2PDMA. Some of these have specific needs to "put" the page while others do not.
This logic to handle any special needs is contained in put_devmap_managed_page(). Therefore all devmap pages should be processed by this function where we can contain the correct logic for a page put. Handle all device type pages within release_pages() by calling put_devmap_managed_page() on all devmap pages. If put_devmap_managed_page() returns true the page has been put and we continue with the next page. A false return of put_devmap_managed_page() means the page did not require special processing and should fall to "normal" processing. This was found via code inspection while determining if release_pages() and the new put_user_pages() could be interchangeable.[1] [1] https://lore.kernel.org/lkml/[email protected]/ Cc: Jérôme Glisse <[email protected]> Cc: Michal Hocko <[email protected]> Reviewed-by: Dan Williams <[email protected]> Reviewed-by: John Hubbard <[email protected]> Signed-off-by: Ira Weiny <[email protected]> --- Changes from V2: Update changelog for more clarity as requested by Michal Update comment WRT "failing" of put_devmap_managed_page() Changes from V1: Add comment clarifying that put_devmap_managed_page() can still fail. Add Reviewed-by tags. mm/swap.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) diff --git a/mm/swap.c b/mm/swap.c index 7ede3eddc12a..6d153ce4cb8c 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -740,15 +740,20 @@ void release_pages(struct page **pages, int nr) if (is_huge_zero_page(page)) continue; - /* Device public page can not be huge page */ - if (is_device_public_page(page)) { + if (is_zone_device_page(page)) { if (locked_pgdat) { spin_unlock_irqrestore(&locked_pgdat->lru_lock, flags); locked_pgdat = NULL; } - put_devmap_managed_page(page); - continue; + /* + * Not all zone-device-pages require special + * processing. Those pages return 'false' from + * put_devmap_managed_page() expecting a call to + * put_page_testzero() + */ + if (put_devmap_managed_page(page)) + continue; } page = compound_head(page); -- 2.20.1
