[PATCH] smaps: Fix the abnormal memory statistics obtained through /proc/pid/smaps

[liubo <liubo254@huawei.com>]

In commit 474098edac26 ("mm/gup: replace FOLL_NUMA by
gup_can_follow_protnone()"), FOLL_NUMA was removed and replaced by
the gup_can_follow_protnone interface.

However, for the case where the user-mode process uses transparent
huge pages, when analyzing the memory usage through
/proc/pid/smaps_rollup, the obtained memory usage is not consistent
with the RSS in /proc/pid/status.

Related examples are as follows:
cat /proc/15427/status
VmRSS:  20973024 kB
RssAnon:        20971616 kB
RssFile:            1408 kB
RssShmem:              0 kB

cat /proc/15427/smaps_rollup
00400000-7ffcc372d000 ---p 00000000 00:00 0 [rollup]
Rss:            14419432 kB
Pss:            14418079 kB
Pss_Dirty:      14418016 kB
Pss_Anon:       14418016 kB
Pss_File:             63 kB
Pss_Shmem:             0 kB
Anonymous:      14418016 kB
LazyFree:              0 kB
AnonHugePages:  14417920 kB

The root cause is that the traversal In the page table, the number of
pages obtained by smaps_pmd_entry does not include the pages
corresponding to PROTNONE,resulting in a different situation.

Therefore, when obtaining pages through the follow_trans_huge_pmd
interface, add the FOLL_FORCE flag to count the pages corresponding to
PROTNONE to solve the above problem.

Signed-off-by: liubo <liubo254@huawei.com>
Fixes: 474098edac26 ("mm/gup: replace FOLL_NUMA by gup_can_follow_protnone()")
---
 fs/proc/task_mmu.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index c1e6531cb02a..ed08f9b869e2 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -571,8 +571,10 @@ static void smaps_pmd_entry(pmd_t *pmd, unsigned long addr,
 	bool migration = false;
 
 	if (pmd_present(*pmd)) {
-		/* FOLL_DUMP will return -EFAULT on huge zero page */
-		page = follow_trans_huge_pmd(vma, addr, pmd, FOLL_DUMP);
+		/* FOLL_DUMP will return -EFAULT on huge zero page
+		 * FOLL_FORCE follow a PROT_NONE mapped page
+		 */
+		page = follow_trans_huge_pmd(vma, addr, pmd, FOLL_DUMP | FOLL_FORCE);
 	} else if (unlikely(thp_migration_supported() && is_swap_pmd(*pmd))) {
 		swp_entry_t entry = pmd_to_swp_entry(*pmd);
 
-- 
2.27.0