When the "struct page size" crosses page boundaries we cannot
make use of this feature. Let free_vmemmap_pages_per_hpage()
return zero if that is the case, most of the functions can be
optimized away.
Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Reviewed-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Reviewed-by: Oscar Salvador <osalvador@xxxxxxx>
---
include/linux/hugetlb.h | 3 ++-
mm/hugetlb_vmemmap.c | 7 +++++++
mm/hugetlb_vmemmap.h | 6 ++++++
3 files changed, 15 insertions(+), 1 deletion(-)
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index c70421e26189..333dd0479fc2 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -880,7 +880,8 @@ extern bool hugetlb_free_vmemmap_enabled;
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));
}
#else
static inline bool is_hugetlb_free_vmemmap_enabled(void)
diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index 33e42678abe3..1ba1ef45c48c 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -265,6 +265,13 @@ void __init hugetlb_vmemmap_init(struct hstate *h)
BUILD_BUG_ON(__NR_USED_SUBPAGE >=
RESERVE_VMEMMAP_SIZE / sizeof(struct page));
+ /*
+ * The compiler can help us to optimize this function to null
+ * when the size of the struct page is not power of 2.
+ */
+ if (!is_power_of_2(sizeof(struct page)))
+ return;
+
if (!hugetlb_free_vmemmap_enabled)
return;
diff --git a/mm/hugetlb_vmemmap.h b/mm/hugetlb_vmemmap.h
index cb2bef8f9e73..29aaaf7b741e 100644
--- a/mm/hugetlb_vmemmap.h
+++ b/mm/hugetlb_vmemmap.h
@@ -21,6 +21,12 @@ void hugetlb_vmemmap_init(struct hstate *h);
*/
static inline unsigned int free_vmemmap_pages_per_hpage(struct hstate *h)
{
+ /*
+ * This check aims to let the compiler help us optimize the code as
+ * much as possible.
+ */
+ if (!is_power_of_2(sizeof(struct page)))
+ return 0;
return h->nr_free_vmemmap_pages;
}
#else
--
2.11.0
