[PATCH] mm: memory: fix /proc/meminfo reporting for MLOCK_ONFAULT

Lucian Adrian Grijincu
2019-09-12T23:19:03Z

As pages are faulted in MLOCK_ONFAULT correctly updates
/proc/self/smaps, but doesn't update /proc/meminfo's Mlocked field.

- Before this /proc/meminfo fields didn't change as pages were faulted in:

```
= Start =
/proc/meminfo
Unevictable: 10128 kB
Mlocked: 10132 kB
= Creating testfile =

= after mlock2(MLOCK_ONFAULT) =
/proc/meminfo
Unevictable: 10128 kB
Mlocked: 10132 kB
/proc/self/smaps
7f8714000000-7f8754000000 rw-s 00000000 08:04 50857050 /root/testfile
Locked: 0 kB

= after reading half of the file =
/proc/meminfo
Unevictable: 10128 kB
Mlocked: 10132 kB
/proc/self/smaps
7f8714000000-7f8754000000 rw-s 00000000 08:04 50857050 /root/testfile
Locked: 524288 kB

= after reading the entire the file =
/proc/meminfo
Unevictable: 10128 kB
Mlocked: 10132 kB
/proc/self/smaps
7f8714000000-7f8754000000 rw-s 00000000 08:04 50857050 /root/testfile
Locked: 1048576 kB

= after munmap =
/proc/meminfo
Unevictable: 10128 kB
Mlocked: 10132 kB
/proc/self/smaps
```

- After: /proc/meminfo fields are properly updated as pages are touched:

```
= Start =
/proc/meminfo
Unevictable: 60 kB
Mlocked: 60 kB
= Creating testfile =

= after mlock2(MLOCK_ONFAULT) =
/proc/meminfo
Unevictable: 60 kB
Mlocked: 60 kB
/proc/self/smaps
7f2b9c600000-7f2bdc600000 rw-s 00000000 08:04 63045798 /root/testfile
Locked: 0 kB

= after reading half of the file =
/proc/meminfo
Unevictable: 524220 kB
Mlocked: 524220 kB
/proc/self/smaps
7f2b9c600000-7f2bdc600000 rw-s 00000000 08:04 63045798 /root/testfile
Locked: 524288 kB

= after reading the entire the file =
/proc/meminfo
Unevictable: 1048496 kB
Mlocked: 1048508 kB
/proc/self/smaps
7f2b9c600000-7f2bdc600000 rw-s 00000000 08:04 63045798 /root/testfile
Locked: 1048576 kB

= after munmap =
/proc/meminfo
Unevictable: 176 kB
Mlocked: 60 kB
/proc/self/smaps
```

Repro code.
---

int mlock2wrap(const void* addr, size_t len, int flags) {
return syscall(SYS_mlock2, addr, len, flags);
}

void smaps() {
char smapscmd[1000];
snprintf(
smapscmd,
sizeof(smapscmd) - 1,
"grep testfile -A 20 /proc/%d/smaps | grep -E '(testfile|Locked)'",
getpid());
printf("/proc/self/smaps\n");
fflush(stdout);
system(smapscmd);
}

void meminfo() {
const char* meminfocmd = "grep -E '(Mlocked|Unevictable)' /proc/meminfo";
printf("/proc/meminfo\n");
fflush(stdout);
system(meminfocmd);
}

{ \
int rc = (call); \
if (rc != 0) { \
printf("error %d %s\n", rc, strerror(errno)); \
exit(1); \
} \
}
int main(int argc, char* argv[]) {
printf("= Start =\n");
meminfo();

printf("= Creating testfile =\n");
size_t size = 1 << 30; // 1 GiB
int fd = open("testfile", O_CREAT | O_RDWR, 0666);
{
void* buf = malloc(size);
write(fd, buf, size);
free(buf);
}
int ret = 0;
void* addr = NULL;
addr = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);

if (argc > 1) {
PCHECK(mlock2wrap(addr, size, MLOCK_ONFAULT));
printf("= after mlock2(MLOCK_ONFAULT) =\n");
meminfo();
smaps();

for (size_t i = 0; i < size / 2; i += 4096) {
ret += ((char*)addr)[i];
}
printf("= after reading half of the file =\n");
meminfo();
smaps();

for (size_t i = 0; i < size; i += 4096) {
ret += ((char*)addr)[i];
}
printf("= after reading the entire the file =\n");
meminfo();
smaps();

} else {
PCHECK(mlock(addr, size));
printf("= after mlock =\n");
meminfo();
smaps();
}

PCHECK(munmap(addr, size));
printf("= after munmap =\n");
meminfo();
smaps();

return ret;
}

---

Signed-off-by: Lucian Adrian Grijincu <lucian@fb.com>
---
mm/memory.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/mm/memory.c b/mm/memory.c
index e0c232fe81d9..7e8dc3ed4e89 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3311,6 +3311,9 @@ vm_fault_t alloc_set_pte(struct vm_fault *vmf, struct mem_cgroup *memcg,
} else {
inc_mm_counter_fast(vma->vm_mm, mm_counter_file(page));
page_add_file_rmap(page, false);
+ if ((vma->vm_flags & (VM_LOCKED | VM_SPECIAL)) == VM_LOCKED &&
+ !PageTransCompound(page))
+ mlock_vma_page(page);
}
set_pte_at(vma->vm_mm, vmf->address, vmf->pte, entry);

--
2.17.1