mm/swap: cache swap migration A/D bits support
Introduce a variable swap_migration_ad_supported to cache whether the arch supports swap migration A/D bits. Here one thing to mention is that SWP_MIG_TOTAL_BITS will internally reference the other macro MAX_PHYSMEM_BITS, which is a function call on x86 (constant on all the rest of archs). It's safe to reference it in swapfile_init() because when reaching here we're already during initcalls level 4 so we must have initialized 5-level pgtable for x86_64 (right after early_identify_cpu() finishes). - start_kernel - setup_arch - early_cpu_init - get_cpu_cap --> fetch from CPUID (including X86_FEATURE_LA57) - early_identify_cpu --> clear X86_FEATURE_LA57 (if early lvl5 not enabled (USE_EARLY_PGTABLE_L5)) - arch_call_rest_init - rest_init - kernel_init - kernel_init_freeable - do_basic_setup - do_initcalls --> calls swapfile_init() (initcall level 4) This should slightly speed up the migration swap entry handlings. Link: https://lkml.kernel.org/r/20220811161331.37055-8-peterx@redhat.comSigned-off-by: Peter Xu <peterx@redhat.com> Cc: Alistair Popple <apopple@nvidia.com> Cc: Andi Kleen <andi.kleen@intel.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: David Hildenbrand <david@redhat.com> Cc: Huang Ying <ying.huang@intel.com> Cc: Hugh Dickins <hughd@google.com> Cc: "Kirill A . Shutemov" <kirill@shutemov.name> Cc: Minchan Kim <minchan@kernel.org> Cc: Nadav Amit <nadav.amit@gmail.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Dave Hansen <dave.hansen@intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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