[PATCH v8 12/12] mm/hugetlb: Optimize the code with the help of the compiler

Muchun Song
2020-12-10T04:01:22Z

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.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
include/linux/hugetlb.h | 3 ++-
mm/hugetlb_vmemmap.c | 3 +++
mm/hugetlb_vmemmap.h | 2 +-
3 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 7295f6b3d55e..adc17765e0e9 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -791,7 +791,8 @@ 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 7f0b9e002be4..819ab9bb9298 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -208,6 +208,9 @@ bool hugetlb_free_vmemmap_enabled;

static int __init early_hugetlb_free_vmemmap_param(char *buf)
{
+ if (!is_power_of_2(sizeof(struct page)))
+ return 0;
+
if (!buf)
return -EINVAL;

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));
}
#else
static inline void hugetlb_vmemmap_init(struct hstate *h)
--
2.11.0