linux-kernel - [PATCH v3 4/9] mm: introduce skip_none

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Message-Id: <574bc9b646c87d878a5048edb63698a1f8483e10.1731566457.git.zhengqi.arch@bytedance.com>
Date: Thu, 14 Nov 2024 14:59:55 +0800
From: Qi Zheng <zhengqi.arch@...edance.com>
To: david@...hat.com,
	jannh@...gle.com,
	hughd@...gle.com,
	willy@...radead.org,
	muchun.song@...ux.dev,
	vbabka@...nel.org,
	akpm@...ux-foundation.org,
	peterx@...hat.com
Cc: mgorman@...e.de,
	catalin.marinas@....com,
	will@...nel.org,
	dave.hansen@...ux.intel.com,
	luto@...nel.org,
	peterz@...radead.org,
	x86@...nel.org,
	lorenzo.stoakes@...cle.com,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	zokeefe@...gle.com,
	rientjes@...gle.com,
	Qi Zheng <zhengqi.arch@...edance.com>
Subject: [PATCH v3 4/9] mm: introduce skip_none_ptes()

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@...hat.com>
Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
---
 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