[PATCH] mm: khugepaged: make scan loops suspend aware

[Sergey Senozhatsky <senozhatsky@chromium.org>]

A number of khugepaaged's loops, e.g. khugepaged_scan_mm_slot(),
are time unbound, which can become problematic during system
suspend:

PM: suspend entry (s2idle)
Filesystems sync: 0.003 seconds
Freezing user space processes
Freezing user space processes completed (elapsed 0.003 seconds)
OOM killer disabled.
Freezing remaining freezable tasks
Freezing remaining freezable tasks failed after 20.004 seconds (1 tasks refusing to freeze, wq_busy=0):
task:khugepaged      state:D stack:0     pid:1345  ppid:2      flags:0x00004000
Call Trace:
 <TASK>
 schedule+0x523/0x16a0
 schedule_timeout+0x23b/0x6e0
 io_schedule_timeout+0x3f/0x80
 wait_for_completion_io_timeout+0xe4/0x170
 submit_bio_wait+0x79/0xc0
 swap_readpage+0x150/0x2d0
 swap_cluster_readahead+0x3be/0x750
 shmem_swapin+0xa7/0x100
 shmem_swapin_folio+0xcd/0x2e0
 shmem_get_folio+0x237/0x580
 collapse_file+0x247/0x1280
 hpage_collapse_scan_file+0x26e/0x380
 khugepaged+0x43b/0x810
 kthread+0xfb/0x120
 </TASK>

Make hpage_collapse_test_exit_or_disable() suspend aware so
that khugepaaged's scan loops can terminate in a timely manner
and let system enter the sleep state.

Co-developed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
---
 mm/khugepaged.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index eff9e3061925..9b3201fb6840 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -392,10 +392,18 @@ static inline int hpage_collapse_test_exit(struct mm_struct *mm)
 	return atomic_read(&mm->mm_users) == 0;
 }
 
-static inline int hpage_collapse_test_exit_or_disable(struct mm_struct *mm)
+static inline int hpage_collapse_test_exit_or_disable(struct mm_struct *mm,
+						struct collapse_control *cc)
 {
+	bool was_frozen = false;
+
+	if (cc->is_khugepaged &&
+	    unlikely(kthread_freezable_should_stop(&was_frozen)))
+		return 1;
+
 	return hpage_collapse_test_exit(mm) ||
-		mm_flags_test(MMF_DISABLE_THP_COMPLETELY, mm);
+		mm_flags_test(MMF_DISABLE_THP_COMPLETELY, mm) ||
+		was_frozen;
 }
 
 static bool hugepage_pmd_enabled(void)
-- 
2.53.0.239.g8d8fc8a987-goog