On Mon, Dec 16, 2019 at 2:26 PM John Hubbard jhubbard@nvidia.com wrote:
An upcoming patch changes and complicates the refcounting and especially the "put page" aspects of it. In order to keep everything clean, refactor the devmap page release routines:
Rename put_devmap_managed_page() to page_is_devmap_managed(), and limit the functionality to "read only": return a bool, with no side effects.
Add a new routine, put_devmap_managed_page(), to handle checking what kind of page it is, and what kind of refcount handling it requires.
Rename __put_devmap_managed_page() to free_devmap_managed_page(), and limit the functionality to unconditionally freeing a devmap page.
This is originally based on a separate patch by Ira Weiny, which applied to an early version of the put_user_page() experiments. Since then, Jérôme Glisse suggested the refactoring described above.
Cc: Christoph Hellwig hch@lst.de Suggested-by: Jérôme Glisse jglisse@redhat.com Reviewed-by: Dan Williams dan.j.williams@intel.com Reviewed-by: Jan Kara jack@suse.cz Signed-off-by: Ira Weiny ira.weiny@intel.com Signed-off-by: John Hubbard jhubbard@nvidia.com
include/linux/mm.h | 17 +++++++++++++---- mm/memremap.c | 16 ++-------------- mm/swap.c | 24 ++++++++++++++++++++++++ 3 files changed, 39 insertions(+), 18 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h index c97ea3b694e6..77a4df06c8a7 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -952,9 +952,10 @@ static inline bool is_zone_device_page(const struct page *page) #endif
#ifdef CONFIG_DEV_PAGEMAP_OPS -void __put_devmap_managed_page(struct page *page); +void free_devmap_managed_page(struct page *page); DECLARE_STATIC_KEY_FALSE(devmap_managed_key); -static inline bool put_devmap_managed_page(struct page *page)
+static inline bool page_is_devmap_managed(struct page *page) { if (!static_branch_unlikely(&devmap_managed_key)) return false; @@ -963,7 +964,6 @@ static inline bool put_devmap_managed_page(struct page *page) switch (page->pgmap->type) { case MEMORY_DEVICE_PRIVATE: case MEMORY_DEVICE_FS_DAX:
__put_devmap_managed_page(page); return true; default: break;@@ -971,7 +971,14 @@ static inline bool put_devmap_managed_page(struct page *page) return false; }
+bool put_devmap_managed_page(struct page *page);
#else /* CONFIG_DEV_PAGEMAP_OPS */ +static inline bool page_is_devmap_managed(struct page *page) +{
return false;+}
static inline bool put_devmap_managed_page(struct page *page) { return false; @@ -1028,8 +1035,10 @@ static inline void put_page(struct page *page) * need to inform the device driver through callback. See * include/linux/memremap.h and HMM for details. */
if (put_devmap_managed_page(page))
if (page_is_devmap_managed(page)) {put_devmap_managed_page(page); return;} if (put_page_testzero(page)) __put_page(page);diff --git a/mm/memremap.c b/mm/memremap.c index e899fa876a62..2ba773859031 100644 --- a/mm/memremap.c +++ b/mm/memremap.c @@ -411,20 +411,8 @@ struct dev_pagemap *get_dev_pagemap(unsigned long pfn, EXPORT_SYMBOL_GPL(get_dev_pagemap);
#ifdef CONFIG_DEV_PAGEMAP_OPS -void __put_devmap_managed_page(struct page *page) +void free_devmap_managed_page(struct page *page) {
int count = page_ref_dec_return(page);/* still busy */if (count > 1)return;/* only triggered by the dev_pagemap shutdown path */if (count == 0) {__put_page(page);return;}/* notify page idle for dax */ if (!is_device_private_page(page)) { wake_up_var(&page->_refcount);@@ -461,5 +449,5 @@ void __put_devmap_managed_page(struct page *page) page->mapping = NULL; page->pgmap->ops->page_free(page); } -EXPORT_SYMBOL(__put_devmap_managed_page); +EXPORT_SYMBOL(free_devmap_managed_page);
This patch does not have a module consumer for free_devmap_managed_page(), so the export should move to the patch that needs the new export.
Also the only reason that put_devmap_managed_page() is EXPORT_SYMBOL instead of EXPORT_SYMBOL_GPL is that there was no practical way to hide the devmap details from evey module in the kernel that did put_page(). I would expect free_devmap_managed_page() to EXPORT_SYMBOL_GPL if it is not inlined into an existing exported static inline api.