linux-kernel - [Patch v2 3/4] mm/mremap: calculate extent in one place

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Message-Id: <20200129002642.13508-4-richardw.yang@linux.intel.com>
Date:   Wed, 29 Jan 2020 08:26:41 +0800
From:   Wei Yang <richardw.yang@...ux.intel.com>
To:     akpm@...ux-foundation.org, aneesh.kumar@...ux.ibm.com,
        kirill@...temov.name, dan.j.williams@...el.com,
        yang.shi@...ux.alibaba.com, thellstrom@...are.com,
        richardw.yang@...ux.intel.com
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org, digetx@...il.com
Subject: [Patch v2 3/4] 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 | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/mremap.c b/mm/mremap.c
index c2af8ba4ba43..b2f3344d090a 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -258,6 +258,9 @@ unsigned long move_page_tables(struct vm_area_struct *vma,
 		extent = next - old_addr;
 		if (extent > old_end - old_addr)
 			extent = old_end - old_addr;
+		next = (new_addr + PMD_SIZE) & PMD_MASK;
+		if (extent > next - new_addr)
+			extent = next - new_addr;
 		old_pmd = get_old_pmd(vma->vm_mm, old_addr);
 		if (!old_pmd)
 			continue;
@@ -301,9 +304,6 @@ unsigned long move_page_tables(struct vm_area_struct *vma,
 
 		if (pte_alloc(new_vma->vm_mm, new_pmd))
 			break;
-		next = (new_addr + PMD_SIZE) & PMD_MASK;
-		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