[patch 115/163] mm/mremap: calculate extent in one place

Andrew Morton
2020-08-07T06:23:48Z

From: Wei Yang <richard.weiyang@linux.alibaba.com>
Subject: 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.

Instead 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.

Link: http://lkml.kernel.org/r/20200708095028.41706-3-richard.weiyang@linux.alibaba.com
Signed-off-by: Wei Yang <richard.weiyang@linux.alibaba.com>
Tested-by: Dmitry Osipenko <digetx@gmail.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Thomas Hellstrom <thellstrom@vmware.com>
Cc: Thomas Hellstrom (VMware) <thomas_os@shipmail.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Yang Shi <yang.shi@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

mm/mremap.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

--- a/mm/mremap.c~mm-mremap-calculate-extent-in-one-place
+++ a/mm/mremap.c
@@ -277,6 +277,9 @@ unsigned long move_page_tables(struct vm
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;
@@ -320,9 +323,6 @@ unsigned long move_page_tables(struct vm

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);
}
_