On 2020-12-10 04:55, Muchun Song wrote:
We cannot optimize if a "struct page" crosses page boundaries. If
it is true, we can optimize the code with the help of a compiler.
When free_vmemmap_pages_per_hpage() returns zero, most functions are
optimized by the compiler.
As I said earlier, I would squash this patch with patch#10 and
remove the !is_power_of_2 check in hugetlb_vmemmap_init and leave
only the check for the boot parameter.
That should be enough.
static inline bool is_hugetlb_free_vmemmap_enabled(void)
{
- return hugetlb_free_vmemmap_enabled;
+ return hugetlb_free_vmemmap_enabled &&
+ is_power_of_2(sizeof(struct page));
Why? hugetlb_free_vmemmap_enabled can only become true
if the is_power_of_2 check succeeds in early_hugetlb_free_vmemmap_param.
The "is_power_of_2" check here can go.
diff --git a/mm/hugetlb_vmemmap.h b/mm/hugetlb_vmemmap.h
index 0a1c0d33a316..5f5e90c81cd2 100644
--- a/mm/hugetlb_vmemmap.h
+++ b/mm/hugetlb_vmemmap.h
@@ -21,7 +21,7 @@ void free_huge_page_vmemmap(struct hstate *h, struct
page *head);
*/
static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate
*h)
{
- return h->nr_free_vmemmap_pages;
+ return h->nr_free_vmemmap_pages && is_power_of_2(sizeof(struct
page));
If hugetlb_free_vmemmap_enabled is false, hugetlb_vmemmap_init() leaves
h->nr_free_vmemmap_pages unset to 0, so no need for the is_power_of_2
check here.
--
Oscar Salvador
SUSE L3
