linux-kernel - [PATCH 3/9] mm/z3fold: remove buggy use of stale list for allocation

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Message-ID: <20220429064051.61552-4-linmiaohe@huawei.com>
Date:   Fri, 29 Apr 2022 14:40:45 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     <akpm@...ux-foundation.org>, <vitaly.wool@...sulko.com>
CC:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        <linmiaohe@...wei.com>
Subject: [PATCH 3/9] mm/z3fold: remove buggy use of stale list for allocation

Currently if z3fold couldn't find an unbuddied page it would first try to
pull a page off the stale list. But this approach is problematic. If init
z3fold page fails later, the page should be freed via free_z3fold_page to
clean up the relevant resource instead of using __free_page directly. And
if page is successfully reused, it will BUG_ON later in __SetPageMovable
because it's already non-lru movable page, i.e. PAGE_MAPPING_MOVABLE is
already set in page->mapping. In order to fix all of these issues, we can
simply remove the buggy use of stale list for allocation because can_sleep
should always be false and we never really hit the reusing code path now.

Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
---
 mm/z3fold.c | 23 +----------------------
 1 file changed, 1 insertion(+), 22 deletions(-)

diff --git a/mm/z3fold.c b/mm/z3fold.c
index 5d8c21f2bc59..4e6814c5694f 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -1102,28 +1102,7 @@ static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp,
 		bud = FIRST;
 	}

-	page = NULL;
-	if (can_sleep) {
-		spin_lock(&pool->stale_lock);
-		zhdr = list_first_entry_or_null(&pool->stale,
-						struct z3fold_header, buddy);
-		/*
-		 * Before allocating a page, let's see if we can take one from
-		 * the stale pages list. cancel_work_sync() can sleep so we
-		 * limit this case to the contexts where we can sleep
-		 */
-		if (zhdr) {
-			list_del(&zhdr->buddy);
-			spin_unlock(&pool->stale_lock);
-			cancel_work_sync(&zhdr->work);
-			page = virt_to_page(zhdr);
-		} else {
-			spin_unlock(&pool->stale_lock);
-		}
-	}
-	if (!page)
-		page = alloc_page(gfp);
-
+	page = alloc_page(gfp);
 	if (!page)
 		return -ENOMEM;

-- 
2.23.0