linux-kernel - [PATCH v2 10/12] mm, swap: no need to truncate the scan border

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Message-Id: <20260128-swap-table-p3-v2-10-fe0b67ef0215@tencent.com>
Date: Wed, 28 Jan 2026 17:28:34 +0800
From: Kairui Song <ryncsn@...il.com>
To: linux-mm@...ck.org
Cc: Andrew Morton <akpm@...ux-foundation.org>, 
 Kemeng Shi <shikemeng@...weicloud.com>, Nhat Pham <nphamcs@...il.com>, 
 Baoquan He <bhe@...hat.com>, Barry Song <baohua@...nel.org>, 
 Johannes Weiner <hannes@...xchg.org>, David Hildenbrand <david@...nel.org>, 
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, 
 Youngjun Park <youngjun.park@....com>, linux-kernel@...r.kernel.org, 
 Chris Li <chrisl@...nel.org>, Kairui Song <kasong@...cent.com>
Subject: [PATCH v2 10/12] mm, swap: no need to truncate the scan border

From: Kairui Song <kasong@...cent.com>

swap_map had a static flexible size, so the last cluster won't be fully
covered, hence the allocator needs to check the scan border to avoid
OOB. But the swap table has a fixed-sized swap table for each cluster,
and the slots beyond the device size are marked as bad slots. The
allocator can simply scan all slots as usual, and any bad slots will be
skipped.

Signed-off-by: Kairui Song <kasong@...cent.com>
---
 mm/swap.h     | 2 +-
 mm/swapfile.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/swap.h b/mm/swap.h
index 751430e2d2a5..9fc5fecdcfdf 100644
--- a/mm/swap.h
+++ b/mm/swap.h
@@ -85,7 +85,7 @@ static inline struct swap_cluster_info *__swap_offset_to_cluster(
 		struct swap_info_struct *si, pgoff_t offset)
 {
 	VM_WARN_ON_ONCE(percpu_ref_is_zero(&si->users)); /* race with swapoff */
-	VM_WARN_ON_ONCE(offset >= si->max);
+	VM_WARN_ON_ONCE(offset >= roundup(si->max, SWAPFILE_CLUSTER));
 	return &si->cluster_info[offset / SWAPFILE_CLUSTER];
 }
 
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 45579ace27ba..a7fc8837eb74 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -945,8 +945,8 @@ static unsigned int alloc_swap_scan_cluster(struct swap_info_struct *si,
 {
 	unsigned int next = SWAP_ENTRY_INVALID, found = SWAP_ENTRY_INVALID;
 	unsigned long start = ALIGN_DOWN(offset, SWAPFILE_CLUSTER);
-	unsigned long end = min(start + SWAPFILE_CLUSTER, si->max);
 	unsigned int order = likely(folio) ? folio_order(folio) : 0;
+	unsigned long end = start + SWAPFILE_CLUSTER;
 	unsigned int nr_pages = 1 << order;
 	bool need_reclaim, ret, usable;
 

-- 
2.52.0