linux-kernel - [Patch v4 2/4] mm/mremap: calculate extent in one place

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Message-Id: <20200708095028.41706-3-richard.weiyang@linux.alibaba.com>
Date:   Wed,  8 Jul 2020 17:50:26 +0800
From:   Wei Yang <richard.weiyang@...ux.alibaba.com>
To:     akpm@...ux-foundation.org, kirill.shutemov@...ux.intel.com,
        vbabka@...e.cz, yang.shi@...ux.alibaba.com, thomas_os@...pmail.org,
        anshuman.khandual@....com, sean.j.christopherson@...el.com,
        richard.weiyang@...ux.alibaba.com, peterx@...hat.com,
        aneesh.kumar@...ux.ibm.com, willy@...radead.org,
        thellstrom@...are.com
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org, digetx@...il.com
Subject: [Patch v4 2/4] 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 <richard.weiyang@...ux.alibaba.com>
Tested-by: Dmitry Osipenko <digetx@...il.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@...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 de27b12c8a5a..a30b3e86cc99 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);
 	}
-- 
2.20.1 (Apple Git-117)