The patch titled
mm: hugetlb: fix hugepage memory leak in walk_page_range()
has been added to the -mm tree. Its filename is
mm-hugetlb-fix-hugepage-memory-leak-in-walk_page_range.patch
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------------------------------------------------------
Subject: mm: hugetlb: fix hugepage memory leak in walk_page_range()
From: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Most callers of pmd_none_or_clear_bad() check whether the target page is
in a hugepage or not, but mincore() and walk_page_range() do not check it.
So if we use mincore() on a hugepage on x86 machine, the hugepage memory
is leaked as shown below. This patch fixes it by extending mincore()
system call to support hugepages.
Details
=======
My test program (leak_mincore) works as follows:
- creat() and mmap() a file on hugetlbfs (file size is 200MB == 100 hugepages,)
- read()/write() something on it,
- call mincore() for first ten pages and printf() the values of *vec
- munmap() and unlink() the file on hugetlbfs
Without my patch
----------------
$ cat /proc/meminfo| grep "HugePage"
HugePages_Total: 1000
HugePages_Free: 1000
HugePages_Rsvd: 0
HugePages_Surp: 0
$ ./leak_mincore
vec[0] 0
vec[1] 0
vec[2] 0
vec[3] 0
vec[4] 0
vec[5] 0
vec[6] 0
vec[7] 0
vec[8] 0
vec[9] 0
$ cat /proc/meminfo |grep "HugePage"
HugePages_Total: 1000
HugePages_Free: 999
HugePages_Rsvd: 0
HugePages_Surp: 0
$ ls /hugetlbfs/
$
Return values in *vec from mincore() are set to 0, while the hugepage
should be in memory, and 1 hugepage is still accounted as used while there
is no file on hugetlbfs.
With my patch
-------------
$ cat /proc/meminfo| grep "HugePage"
HugePages_Total: 1000
HugePages_Free: 1000
HugePages_Rsvd: 0
HugePages_Surp: 0
$ ./leak_mincore
vec[0] 1
vec[1] 1
vec[2] 1
vec[3] 1
vec[4] 1
vec[5] 1
vec[6] 1
vec[7] 1
vec[8] 1
vec[9] 1
$ cat /proc/meminfo |grep "HugePage"
HugePages_Total: 1000
HugePages_Free: 1000
HugePages_Rsvd: 0
HugePages_Surp: 0
$ ls /hugetlbfs/
$
Return value in *vec set to 1 and no memory leaks.
Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Cc: Wu Fengguang <fengguang.wu@xxxxxxxxx>
Cc: Hugh Dickins <hugh.dickins@xxxxxxxxxxxxx>
Cc: Mel Gorman <mel@xxxxxxxxx>
Cc: Lee Schermerhorn <lee.schermerhorn@xxxxxx>
Cc: Andy Whitcroft <apw@xxxxxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/pagewalk.c | 15 ++++++++++++++-
1 file changed, 14 insertions(+), 1 deletion(-)
diff -puN mm/pagewalk.c~mm-hugetlb-fix-hugepage-memory-leak-in-walk_page_range mm/pagewalk.c
--- a/mm/pagewalk.c~mm-hugetlb-fix-hugepage-memory-leak-in-walk_page_range
+++ a/mm/pagewalk.c
@@ -1,6 +1,7 @@
#include <linux/mm.h>
#include <linux/highmem.h>
#include <linux/sched.h>
+#include <linux/hugetlb.h>
static int walk_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
struct mm_walk *walk)
@@ -107,6 +108,7 @@ int walk_page_range(unsigned long addr,
pgd_t *pgd;
unsigned long next;
int err = 0;
+ struct vm_area_struct *vma;
if (addr >= end)
return err;
@@ -117,11 +119,21 @@ int walk_page_range(unsigned long addr,
pgd = pgd_offset(walk->mm, addr);
do {
next = pgd_addr_end(addr, end);
+
+ /* skip hugetlb vma to avoid hugepage PMD being cleared
+ * in pmd_none_or_clear_bad(). */
+ vma = find_vma(walk->mm, addr);
+ if (is_vm_hugetlb_page(vma)) {
+ next = (vma->vm_end < next) ? vma->vm_end : next;
+ continue;
+ }
+
if (pgd_none_or_clear_bad(pgd)) {
if (walk->pte_hole)
err = walk->pte_hole(addr, next, walk);
if (err)
break;
+ pgd++;
continue;
}
if (walk->pgd_entry)
@@ -131,7 +143,8 @@ int walk_page_range(unsigned long addr,
err = walk_pud_range(pgd, addr, next, walk);
if (err)
break;
- } while (pgd++, addr = next, addr != end);
+ pgd++;
+ } while (addr = next, addr != end);
return err;
}
_
Patches currently in -mm which might be from n-horiguchi@xxxxxxxxxxxxx are
mm-hugetlb-fix-hugepage-memory-leak-in-mincore.patch
mm-hugetlb-fix-hugepage-memory-leak-in-mincore-cleanup.patch
mm-hugetlb-fix-hugepage-memory-leak-in-walk_page_range.patch
mm-hugetlb-add-hugepage-support-to-pagemap.patch
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