[RFC PATCH 10/26] hugetlb: add for_each_hgm_shift

[James Houghton]

This is a helper macro to loop through all the usable page sizes for a
high-granularity-enabled HugeTLB VMA. Given the VMA's hstate, it will
loop, in descending order, through the page sizes that HugeTLB supports
for this architecture; it always includes PAGE_SIZE.

Signed-off-by: James Houghton <jthoughton@xxxxxxxxxx>
---
 mm/hugetlb.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 8b10b941458d..557b0afdb503 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -6989,6 +6989,16 @@ bool hugetlb_hgm_enabled(struct vm_area_struct *vma)
 	/* All shared VMAs have HGM enabled. */
 	return vma->vm_flags & VM_SHARED;
 }
+static unsigned int __shift_for_hstate(struct hstate *h)
+{
+	if (h >= &hstates[hugetlb_max_hstate])
+		return PAGE_SHIFT;
+	return huge_page_shift(h);
+}
+#define for_each_hgm_shift(hstate, tmp_h, shift) \
+	for ((tmp_h) = hstate; (shift) = __shift_for_hstate(tmp_h), \
+			       (tmp_h) <= &hstates[hugetlb_max_hstate]; \
+			       (tmp_h)++)
 #endif /* CONFIG_HUGETLB_HIGH_GRANULARITY_MAPPING */
 
 /*
-- 
2.37.0.rc0.161.g10f37bed90-goog