linux-kernel - [PATCH 4/5] mm/mremap: calculate extent in one place

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Date:   Sat, 18 Jan 2020 07:22:53 +0800
From:   Wei Yang <richardw.yang@...ux.intel.com>
To:     akpm@...ux-foundation.org, dan.j.williams@...el.com,
        aneesh.kumar@...ux.ibm.com, kirill@...temov.name,
        yang.shi@...ux.alibaba.com, richardw.yang@...ux.intel.com,
        thellstrom@...are.com
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: [PATCH 4/5] mm/mremap: calculate extent in one place

Page tables is moved on the base of PMD. This requires both source
and destination range should meet the requirement.

Current code works well since move_huge_pmd() and move_normal_pmd()
would check old_addr and new_addr again. And then return to move_ptes()
if the either of them is not aligned.

In stead of calculating the extent separately, it is better to calculate
in one place, so we know it is not necessary to try move pmd. By doing
so, the logic seems a little clear.

Signed-off-by: Wei Yang <richardw.yang@...ux.intel.com>
---
 mm/mremap.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/mm/mremap.c b/mm/mremap.c
index a258914f3ee1..37335a10779d 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -240,7 +240,7 @@ unsigned long move_page_tables(struct vm_area_struct *vma,
 		unsigned long new_addr, unsigned long len,
 		bool need_rmap_locks)
 {
-	unsigned long extent, next, old_end;
+	unsigned long extent, old_next, new_next, old_end;
 	struct mmu_notifier_range range;
 	pmd_t *old_pmd, *new_pmd;
 
@@ -253,8 +253,9 @@ unsigned long move_page_tables(struct vm_area_struct *vma,
 
 	for (; old_addr < old_end; old_addr += extent, new_addr += extent) {
 		cond_resched();
-		next = pmd_addr_end(old_addr, old_end);
-		extent = next - old_addr;
+		old_next = pmd_addr_end(old_addr, old_end);
+		new_next = pmd_addr_end(new_addr, new_addr + len);
+		extent = min((old_next - old_addr), (new_next - new_addr));
 		old_pmd = get_old_pmd(vma->vm_mm, old_addr);
 		if (!old_pmd)
 			continue;
@@ -298,9 +299,6 @@ unsigned long move_page_tables(struct vm_area_struct *vma,
 
 		if (pte_alloc(new_vma->vm_mm, new_pmd))
 			break;
-		next = pmd_addr_end(new_addr, new_addr + len);
-		if (extent > next - new_addr)
-			extent = next - new_addr;
 		move_ptes(vma, old_pmd, old_addr, old_addr + extent, new_vma,
 			  new_pmd, new_addr, need_rmap_locks);
 	}
-- 
2.17.1