From: John Hubbard <jhubbard@xxxxxxxxxx>
Subject: mm/gup_benchmark: fix MAP_HUGETLB case
The MAP_HUGETLB ("-H" option) of gup_benchmark fails:
$ sudo ./gup_benchmark -H
mmap: Invalid argument
This is because gup_benchmark.c is passing in a file descriptor to mmap(),
but the fd came from opening up the /dev/zero file. This confuses the
mmap syscall implementation, which thinks that, if the caller did not
specify MAP_ANONYMOUS, then the file must be a huge page file. So it
attempts to verify that the file really is a huge page file, as you can
see here:
ksys_mmap_pgoff()
{
if (!(flags & MAP_ANONYMOUS)) {
retval = -EINVAL;
if (unlikely(flags & MAP_HUGETLB && !is_file_hugepages(file)))
goto out_fput; /* THIS IS WHERE WE END UP */
else if (flags & MAP_HUGETLB) {
...proceed normally, /dev/zero is ok here...
...and of course is_file_hugepages() returns "false" for the /dev/zero
file.
The problem is that the user space program, gup_benchmark.c, really just
wants anonymous memory here. The simplest way to get that is to pass
MAP_ANONYMOUS whenever MAP_HUGETLB is specified, so that's what this patch
does.
Link: http://lkml.kernel.org/r/20191021212435.398153-2-jhubbard@xxxxxxxxxx
Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx>
Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Reviewed-by: Jérôme Glisse <jglisse@xxxxxxxxxx>
Cc: Keith Busch <keith.busch@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
tools/testing/selftests/vm/gup_benchmark.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/tools/testing/selftests/vm/gup_benchmark.c~mm-gup_benchmark-fix-map_hugetlb-case
+++ a/tools/testing/selftests/vm/gup_benchmark.c
@@ -71,7 +71,7 @@ int main(int argc, char **argv)
flags |= MAP_SHARED;
break;
case 'H':
- flags |= MAP_HUGETLB;
+ flags |= (MAP_HUGETLB | MAP_ANONYMOUS);
break;
default:
return -1;
_
