On 12/18/19 8:04 AM, Kirill A. Shutemov wrote:
On Mon, Dec 16, 2019 at 02:25:16PM -0800, John Hubbard 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.
What the reason to separate put_devmap_managed_page() from free_devmap_managed_page() if free_devmap_managed_page() has exacly one caller? Is it preparation for the next patches?
Yes. A later patch, #23, adds another caller: __unpin_devmap_managed_user_page().
...
@@ -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);put_devmap_managed_page() has yet another page_is_devmap_managed() check inside. It looks strange.
Good point, it's an extra unnecessary check. So to clean it up, I'll note that the "if" check is required here in put_page(), in order to stay out of non-inlined function calls in the hot path (put_page()). So I'll do the following:
* Leave the above code as it is here
* Simplify put_devmap_managed_page(), it was trying to do two separate things, and those two things have different requirements. So change it to a void function, with a WARN_ON_ONCE to assert that page_is_devmap_managed() is true,
* And change the other caller (release_pages()) to do that check.
...
@@ -1102,3 +1102,27 @@ void __init swap_setup(void) * _really_ don't want to cluster much more */ }
+#ifdef CONFIG_DEV_PAGEMAP_OPS +bool put_devmap_managed_page(struct page *page) +{
- bool is_devmap = page_is_devmap_managed(page);
- if (is_devmap) {
Reversing the condition would save you an indentation level.
Yes. Done.
I'll also git-reply with an updated patch so you can see what it looks like.
thanks,