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.com
Signed-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>

diff --git a/include/linux/swapfile.h b/include/linux/swapfile.h
index e2d11ae..7ed529a 100644 (file)
--- a/include/linux/swapfile.h
+++ b/include/linux/swapfile.h
@@ -12,5 +12,7 @@ unsigned long arch_max_swapfile_size(void);
 
 /* Maximum swapfile size supported for the arch (not inclusive). */
 extern unsigned long swapfile_maximum_size;
+/* Whether swap migration entry supports storing A/D bits for the arch */
+extern bool swap_migration_ad_supported;
 
 #endif /* _LINUX_SWAPFILE_H */

diff --git a/include/linux/swapops.h b/include/linux/swapops.h
index 027b409..86b95cc 100644 (file)
--- a/include/linux/swapops.h
+++ b/include/linux/swapops.h
@@ -301,13 +301,8 @@ static inline swp_entry_t make_writable_migration_entry(pgoff_t offset)
  */
 static inline bool migration_entry_supports_ad(void)
 {
-       /*
-        * max_swapfile_size() returns the max supported swp-offset plus 1.
-        * We can support the migration A/D bits iff the pfn swap entry has
-        * the offset large enough to cover all of them (PFN, A & D bits).
-        */
 #ifdef CONFIG_SWAP
-       return swapfile_maximum_size >= (1UL << SWP_MIG_TOTAL_BITS);
+       return swap_migration_ad_supported;
 #else  /* CONFIG_SWAP */
        return false;
 #endif /* CONFIG_SWAP */

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 3cc6439..263b19e 100644 (file)
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -64,6 +64,9 @@ EXPORT_SYMBOL_GPL(nr_swap_pages);
 long total_swap_pages;
 static int least_priority = -1;
 unsigned long swapfile_maximum_size;
+#ifdef CONFIG_MIGRATION
+bool swap_migration_ad_supported;
+#endif /* CONFIG_MIGRATION */
 
 static const char Bad_file[] = "Bad swap file entry ";
 static const char Unused_file[] = "Unused swap file entry ";
@@ -3680,6 +3683,11 @@ static int __init swapfile_init(void)
 
        swapfile_maximum_size = arch_max_swapfile_size();
 
+#ifdef CONFIG_MIGRATION
+       if (swapfile_maximum_size >= (1UL << SWP_MIG_TOTAL_BITS))
+               swap_migration_ad_supported = true;
+#endif /* CONFIG_MIGRATION */
+
        return 0;
 }
 subsys_initcall(swapfile_init);