mm, swap: no need to truncate the scan border

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.

Link: https://lkml.kernel.org/r/20260218-swap-table-p3-v3-10-f4e34be021a7@tencent.com
Signed-off-by: Kairui Song <kasong@tencent.com>
Acked-by: Chris Li <chrisl@kernel.org>
Cc: Baoquan He <bhe@redhat.com>
Cc: Barry Song <baohua@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kairui Song <ryncsn@gmail.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: kernel test robot <lkp@intel.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/swap.h b/mm/swap.h
index 0a91e21e92b144bc18e93a76e332eaa5954a65e0..cc410b94e91ad39abe0c9f90df6568826daa6350 100644 (file)
--- 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 cf976ecae8a801297e6bcf7aca216e254336dc97..4442c90407642a3e2555bf74d674f54d8bd59b94 100644 (file)
--- 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;