[PATCH] thp: reduce khugepaged freezing latency

[Andrea Arcangeli <aarcange@redhat.com>]

Lack of set_freezable_with_signal() prevented khugepaged to be waken
up (and prevented to sleep again) across the
schedule_timeout_interruptible() calls after freezing() becomes
true. The tight loop in khugepaged_alloc_hugepage() also missed one
try_to_freeze() call in case alloc_hugepage() would repeatedly fail in
turn preventing the loop to break and to reach the try_to_freeze() in
the khugepaged main loop.

khugepaged would still freeze just fine by trying again the next
minute but it's better if it freezes immediately.

Reported-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
---
 mm/huge_memory.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 4298aba..67311d1 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2277,6 +2277,7 @@ static struct page *khugepaged_alloc_hugepage(void)
 		if (!hpage) {
 			count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
 			khugepaged_alloc_sleep();
+			try_to_freeze();
 		} else
 			count_vm_event(THP_COLLAPSE_ALLOC);
 	} while (unlikely(!hpage) &&
@@ -2331,7 +2332,7 @@ static int khugepaged(void *none)
 {
 	struct mm_slot *mm_slot;
 
-	set_freezable();
+	set_freezable_with_signal();
 	set_user_nice(current, 19);
 
 	/* serialize with start_khugepaged() */

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