mm, swap: clean up swapon process and locking

Slightly clean up the swapon process.  Add comments about what swap_lock
protects, introduce and rename helpers that wrap swap_map and cluster_info
setup, and do it outside of the swap_lock lock.

This lock protection is not needed for swap_map and cluster_info setup
because all swap users must either hold the percpu ref or hold a stable
allocated swap entry (e.g., locking a folio in the swap cache) before
accessing.  So before the swap device is exposed by enable_swap_info,
nothing would use the swap device's map or cluster.

So we are safe to allocate and set up swap data freely first, then expose
the swap device and set the SWP_WRITEOK flag.

Link: https://lkml.kernel.org/r/20260218-swap-table-p3-v3-2-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>

0 files changed, 0 insertions, 0 deletions