[PATCH v3 2/3] mm: memory-hotplug: check folio ref count first in do_migrate_range

[Wupeng Ma <mawupeng1@huawei.com>]

From: Ma Wupeng <mawupeng1@huawei.com>

If a folio has an increased reference count, folio_try_get() will acquire
it, perform necessary operations, and then release it. In the case of a
poisoned folio without an elevated reference count (which is unlikely for
memory-failure), folio_try_get() will simply bypass it.

Therefore, relocate the folio_try_get() function, responsible for checking
and acquiring this reference count at first.

Signed-off-by: Ma Wupeng <mawupeng1@huawei.com>
---
 mm/memory_hotplug.c | 20 +++++++-------------
 1 file changed, 7 insertions(+), 13 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 3de661e57e92..3669b3e2d962 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1795,12 +1795,12 @@ static void do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
 		if (folio_test_large(folio))
 			pfn = folio_pfn(folio) + folio_nr_pages(folio) - 1;
 
-		/*
-		 * HWPoison pages have elevated reference counts so the migration would
-		 * fail on them. It also doesn't make any sense to migrate them in the
-		 * first place. Still try to unmap such a page in case it is still mapped
-		 * (keep the unmap as the catch all safety net).
-		 */
+		if (!folio_try_get(folio))
+			continue;
+
+		if (unlikely(page_folio(page) != folio))
+			goto put_folio;
+
 		if (folio_test_hwpoison(folio) ||
 		    (folio_test_large(folio) && folio_test_has_hwpoisoned(folio))) {
 			if (WARN_ON(folio_test_lru(folio)))
@@ -1808,14 +1808,8 @@ static void do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
 			if (folio_mapped(folio))
 				unmap_poisoned_folio(folio, pfn, false);
 
-			continue;
-		}
-
-		if (!folio_try_get(folio))
-			continue;
-
-		if (unlikely(page_folio(page) != folio))
 			goto put_folio;
+		}
 
 		if (!isolate_folio_to_list(folio, &source)) {
 			if (__ratelimit(&migrate_rs)) {
-- 
2.43.0