[PATCH v2] mm: align larger anonymous mappings on THP boundaries

[Rik van Riel]

Align larger anonymous memory mappings on THP boundaries by
going through thp_get_unmapped_area if THPs are enabled for
the current process.

With this patch, larger anonymous mappings are now THP aligned.
When a malloc library allocates a 2MB or larger arena, that
arena can now be mapped with THPs right from the start, which
can result in better TLB hit rates and execution time.

Signed-off-by: Rik van Riel <riel@xxxxxxxxxxx>
---
v2: avoid the chicken & egg issue with MMF_VM_HUGEPAGE (Yang Shi)

 mm/mmap.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/mmap.c b/mm/mmap.c
index c035020d0c89..1d859893436d 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2229,6 +2229,9 @@ get_unmapped_area(struct file *file, unsigned long addr, unsigned long len,
 		 */
 		pgoff = 0;
 		get_area = shmem_get_unmapped_area;
+	} else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
+		/* Ensures that larger anonymous mappings are THP aligned. */
+		get_area = thp_get_unmapped_area;
 	}
 
 	addr = get_area(file, addr, len, pgoff, flags);
-- 
2.37.1