+ mm-hugetlbc-fix-unnecessary-address-expansion-of-pmd-sharing.patch added to -mm tree

[akpm@linux-foundation.org]

The patch titled
     Subject: mm/hugetlb.c: fix unnecessary address expansion of pmd sharing
has been added to the -mm tree.  Its filename is
     mm-hugetlbc-fix-unnecessary-address-expansion-of-pmd-sharing.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/mm-hugetlbc-fix-unnecessary-address-expansion-of-pmd-sharing.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/mm-hugetlbc-fix-unnecessary-address-expansion-of-pmd-sharing.patch

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------------------------------------------------------
From: Li Xinhai <lixinhai.lxh@gmail.com>
Subject: mm/hugetlb.c: fix unnecessary address expansion of pmd sharing

The current code would unnecessarily expand the address range.  Consider
one example, (start, end) = (1G-2M, 3G+2M), and (vm_start, vm_end) =
(1G-4M, 3G+4M), the expected adjustment should be keep (1G-2M, 3G+2M)
without expand.  But the current result will be (1G-4M, 3G+4M).  Actually,
the range (1G-4M, 1G) and (3G, 3G+4M) would never been involved in pmd
sharing.

After this patch, we will check that the vma span at least one PUD aligned
size and the start,end range overlap the aligned range of vma.

With above example, the aligned vma range is (1G, 3G), so if (start, end)
range is within (1G-4M, 1G), or within (3G, 3G+4M), then no adjustment to
both start and end.  Otherwise, we will have chance to adjust start
downwards or end upwards without exceeding (vm_start, vm_end).

Link: https://lkml.kernel.org/r/20210104081631.2921415-1-lixinhai.lxh@gmail.com
Fixes: 75802ca66354 ("mm/hugetlb: fix calculation of adjust_range_if_pmd_sharing_possible")
Signed-off-by: Li Xinhai <lixinhai.lxh@gmail.com>
Suggested-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/hugetlb.c |   22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

--- a/mm/hugetlb.c~mm-hugetlbc-fix-unnecessary-address-expansion-of-pmd-sharing
+++ a/mm/hugetlb.c
@@ -5259,21 +5259,23 @@ static bool vma_shareable(struct vm_area
 void adjust_range_if_pmd_sharing_possible(struct vm_area_struct *vma,
 				unsigned long *start, unsigned long *end)
 {
-	unsigned long a_start, a_end;
+	unsigned long v_start = ALIGN(vma->vm_start, PUD_SIZE),
+		v_end = ALIGN_DOWN(vma->vm_end, PUD_SIZE);
 
-	if (!(vma->vm_flags & VM_MAYSHARE))
+	/*
+	 * vma need span at least one aligned PUD size and the start,end range
+	 * must at least partialy within it.
+	 */
+	if (!(vma->vm_flags & VM_MAYSHARE) || !(v_end > v_start) ||
+		(*end <= v_start) || (*start >= v_end))
 		return;
 
 	/* Extend the range to be PUD aligned for a worst case scenario */
-	a_start = ALIGN_DOWN(*start, PUD_SIZE);
-	a_end = ALIGN(*end, PUD_SIZE);
+	if (*start > v_start)
+		*start = ALIGN_DOWN(*start, PUD_SIZE);
 
-	/*
-	 * Intersect the range with the vma range, since pmd sharing won't be
-	 * across vma after all
-	 */
-	*start = max(vma->vm_start, a_start);
-	*end = min(vma->vm_end, a_end);
+	if (*end < v_end)
+		*end = ALIGN(*end, PUD_SIZE);
 }
 
 /*
_

Patches currently in -mm which might be from lixinhai.lxh@gmail.com are

mm-hugetlbc-fix-unnecessary-address-expansion-of-pmd-sharing.patch