mm: memory-hotplug: check folio ref count first in do_migrate_range

commit 773b9a6
Author: Ma Wupeng <[email protected]>
Date:   Mon Feb 17 09:43:28 2025 +0800

    mm: memory-hotplug: check folio ref count first in do_migrate_range

    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.

    Link: https://lkml.kernel.org/r/[email protected]
    Signed-off-by: Ma Wupeng <[email protected]>
    Acked-by: David Hildenbrand <[email protected]>
    Acked-by: Miaohe Lin <[email protected]>
    Cc: Michal Hocko <[email protected]>
    Cc: Naoya Horiguchi <[email protected]>
    Cc: Oscar Salvador <[email protected]>
    Cc: <[email protected]>
    Signed-off-by: Andrew Morton <[email protected]>

JIRA: https://issues.redhat.com/browse/RHEL-77742
Signed-off-by: Nico Pache <[email protected]>

Author: PacheNico

mm/memory_hotplug.c

@@ -1795,27 +1795,21 @@ 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)))
 				folio_isolate_lru(folio);
 			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)) {