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,
--
John Hubbard
NVIDIA
