[PATCH v3 4/9] mm: introduce skip_none_ptes()

[Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>]

This commit introduces skip_none_ptes() to skip over all consecutive none
ptes in zap_pte_range(), which helps optimize away need_resched() +
force_break + incremental pte/addr increments etc.

Suggested-by: David Hildenbrand <david@xxxxxxxxxx>
Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
---
 mm/memory.c | 34 ++++++++++++++++++++++++++++++----
 1 file changed, 30 insertions(+), 4 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index bd9ebe0f4471f..24633d0e1445a 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1657,6 +1657,28 @@ static inline int zap_nonpresent_ptes(struct mmu_gather *tlb,
 	return nr;
 }
 
+static inline int skip_none_ptes(pte_t *pte, unsigned long addr,
+				 unsigned long end)
+{
+	pte_t ptent = ptep_get(pte);
+	int max_nr;
+	int nr;
+
+	if (!pte_none(ptent))
+		return 0;
+
+	max_nr = (end - addr) / PAGE_SIZE;
+	nr = 1;
+
+	for (; nr < max_nr; nr++) {
+		ptent = ptep_get(pte + nr);
+		if (!pte_none(ptent))
+			break;
+	}
+
+	return nr;
+}
+
 static unsigned long zap_pte_range(struct mmu_gather *tlb,
 				struct vm_area_struct *vma, pmd_t *pmd,
 				unsigned long addr, unsigned long end,
@@ -1682,13 +1704,17 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
 		pte_t ptent = ptep_get(pte);
 		int max_nr;
 
-		nr = 1;
-		if (pte_none(ptent))
-			continue;
-
 		if (need_resched())
 			break;
 
+		nr = skip_none_ptes(pte, addr, end);
+		if (nr) {
+			addr += PAGE_SIZE * nr;
+			if (addr == end)
+				break;
+			pte += nr;
+		}
+
 		max_nr = (end - addr) / PAGE_SIZE;
 		if (pte_present(ptent)) {
 			nr = zap_present_ptes(tlb, vma, pte, ptent, max_nr,
-- 
2.20.1