linux-kernel - [PATCH v2 3/3] mm: memory-hotplug: check folio ref count first in do_migrate

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Message-ID: <20250116061657.227027-4-mawupeng1@huawei.com>
Date: Thu, 16 Jan 2025 14:16:57 +0800
From: Wupeng Ma <mawupeng1@...wei.com>
To: <akpm@...ux-foundation.org>, <david@...hat.com>, <osalvador@...e.de>,
	<nao.horiguchi@...il.com>, <linmiaohe@...wei.com>, <mhocko@...e.com>
CC: <mawupeng1@...wei.com>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>
Subject: [PATCH v2 3/3] mm: memory-hotplug: check folio ref count first in do_migrate_rang

From: Ma Wupeng <mawupeng1@...wei.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@...wei.com>
---
 mm/memory_hotplug.c | 14 ++++----------
 1 file changed, 4 insertions(+), 10 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 2815bd4ea483..3fb75ee185c6 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1786,6 +1786,9 @@ static void do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
 		page = pfn_to_page(pfn);
 		folio = page_folio(page);
 
+		if (!folio_try_get(folio))
+			continue;
+
 		/*
 		 * No reference or lock is held on the folio, so it might
 		 * be modified concurrently (e.g. split).  As such,
@@ -1795,12 +1798,6 @@ 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_test_hwpoison(folio) ||
 		    (folio_test_large(folio) && folio_test_has_hwpoisoned(folio))) {
 			if (WARN_ON(folio_test_lru(folio)))
@@ -1811,12 +1808,9 @@ static void do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
 				folio_unlock(folio);
 			}
 
-			continue;
+			goto put_folio;
 		}
 
-		if (!folio_try_get(folio))
-			continue;
-
 		if (unlikely(page_folio(page) != folio))
 			goto put_folio;
 
-- 
2.43.0