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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>

authored by

Kairui Song and committed by
Andrew Morton 45711d44 0d6af9bc

+2 -2
+1 -1
mm/swap.h
··· 85 85 struct swap_info_struct *si, pgoff_t offset) 86 86 { 87 87 VM_WARN_ON_ONCE(percpu_ref_is_zero(&si->users)); /* race with swapoff */ 88 - VM_WARN_ON_ONCE(offset >= si->max); 88 + VM_WARN_ON_ONCE(offset >= roundup(si->max, SWAPFILE_CLUSTER)); 89 89 return &si->cluster_info[offset / SWAPFILE_CLUSTER]; 90 90 } 91 91
+1 -1
mm/swapfile.c
··· 945 945 { 946 946 unsigned int next = SWAP_ENTRY_INVALID, found = SWAP_ENTRY_INVALID; 947 947 unsigned long start = ALIGN_DOWN(offset, SWAPFILE_CLUSTER); 948 - unsigned long end = min(start + SWAPFILE_CLUSTER, si->max); 949 948 unsigned int order = likely(folio) ? folio_order(folio) : 0; 949 + unsigned long end = start + SWAPFILE_CLUSTER; 950 950 unsigned int nr_pages = 1 << order; 951 951 bool need_reclaim, ret, usable; 952 952