From 8801a1510bd35b935fd6621e8e38e7aee726d99e Mon Sep 17 00:00:00 2001
From: "Liam R. Howlett" <Liam.Howlett@Oracle.com>
Date: Mon, 21 Sep 2020 12:22:15 -0400
Subject: [PATCH] mm: Change mmap do_brk_flags() to populate the existing VMA

do_brk_flags has already located the modified VMA, so just populate the
region.  Add mm_populate_vma() to mm/gup.c and call the new function
which ignores errors.

Benckmarks in KVM before:
$ ./mmtests/work/sources/wis-0-installed/brk1_threads
testcase:brk increase/decrease of one page
warmup
min:886150 max:886150 total:886150
min:901488 max:901488 total:901488
min:897594 max:897594 total:897594
min:897422 max:897422 total:897422
min:900700 max:900700 total:900700
min:900714 max:900714 total:900714
measurement
min:903016 max:903016 total:903016
min:901224 max:901224 total:901224
min:902626 max:902626 total:902626
min:900518 max:900518 total:900518

Benchmark in KVM after change:
/mmtests/work/sources/wis-0-installed/brk1_threads
testcase:brk increase/decrease of one page
warmup
min:895650 max:895650 total:895650
min:904936 max:904936 total:904936
min:904776 max:904776 total:904776
min:905358 max:905358 total:905358
min:908792 max:908792 total:908792
min:907648 max:907648 total:907648
measurement
min:904368 max:904368 total:904368
min:903936 max:903936 total:903936
min:904720 max:904720 total:904720
min:906626 max:906626 total:906626

Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
---
 mm/gup.c  | 20 ++++++++++++++++++++
 mm/mmap.c |  2 +-
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/mm/gup.c b/mm/gup.c
index 98eb8e6d2609..b06e2a6d9018 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1431,6 +1431,26 @@ long populate_vma_page_range(struct vm_area_struct *vma,
 				NULL, NULL, locked);
 }
 
+/*
+ * mm_populate_vma() - Populate a single range in a single vma.
+ * @vma: The vma to populate.
+ * @start: The start address to populate
+ * @end: The end address to stop populating
+ *
+ * Note: Ignores errors.
+ */
+void mm_populate_vma(struct vm_area_struct *vma, unsigned long start,
+		unsigned long end)
+{
+	struct mm_struct *mm = current->mm;
+	int locked = 1;
+
+	mmap_read_lock(mm);
+	populate_vma_page_range(vma, start, end, &locked);
+	if (locked)
+		mmap_read_unlock(mm);
+}
+
 /*
  * __mm_populate - populate and/or mlock pages within a range of address space.
  *
diff --git a/mm/mmap.c b/mm/mmap.c
index 46ea4a9748d8..968305485c8c 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -277,7 +277,7 @@ success:
 		mmap_write_unlock(mm);
 	userfaultfd_unmap_complete(mm, &uf);
 	if (populate)
-		mm_populate(oldbrk, newbrk - oldbrk);
+		mm_populate_vma(vma_brk, oldbrk, newbrk);
 	return brk;
 
 out:
-- 
2.50.1