mm/mm_init: use node's number of cpus in deferred_page_init_max_threads

x86_64 is already using the node's cpu as maximum threads.  Make that the
default for all archs setting DEFERRED_STRUCT_PAGE_INIT.

This returns to the behavior prior making the function arch-specific with
commit ecd096506922 ("mm: make deferred init's max threads
arch-specific").

Setting DEFERRED_STRUCT_PAGE_INIT and testing on a few arm64 platforms
shows faster deferred_init_memmap completions:

|         | x13s        | SA8775p-ride | Ampere R137-P31 | Ampere HR330 |
|         | Metal, 32GB | VM, 36GB     | VM, 58GB        | Metal, 128GB |
|         | 8cpus       | 8cpus        | 8cpus           | 32cpus       |
|---------|-------------|--------------|-----------------|--------------|
| threads |  ms     (%) | ms       (%) |  ms         (%) |  ms      (%) |
|---------|-------------|--------------|-----------------|--------------|
| 1       | 108    (0%) | 72      (0%) | 224        (0%) | 324     (0%) |
| cpus    |  24  (-77%) | 36    (-50%) |  40      (-82%) |  56   (-82%) |

Michael Ellerman reported:

: On a machine here (1TB, 40 cores, 4KB pages) the existing code gives:
: 
:   [    0.500124] node 2 deferred pages initialised in 210ms
:   [    0.515790] node 3 deferred pages initialised in 230ms
:   [    0.516061] node 0 deferred pages initialised in 230ms
:   [    0.516522] node 7 deferred pages initialised in 230ms
:   [    0.516672] node 4 deferred pages initialised in 230ms
:   [    0.516798] node 6 deferred pages initialised in 230ms
:   [    0.517051] node 5 deferred pages initialised in 230ms
:   [    0.523887] node 1 deferred pages initialised in 240ms
: 
: vs with the patch:
: 
:   [    0.379613] node 0 deferred pages initialised in 90ms
:   [    0.380388] node 1 deferred pages initialised in 90ms
:   [    0.380540] node 4 deferred pages initialised in 100ms
:   [    0.390239] node 6 deferred pages initialised in 100ms
:   [    0.390249] node 2 deferred pages initialised in 100ms
:   [    0.390786] node 3 deferred pages initialised in 110ms
:   [    0.396721] node 5 deferred pages initialised in 110ms
:   [    0.397095] node 7 deferred pages initialised in 110ms
: 
: Which is a nice speedup.

[[email protected]: v3]
  Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Eric Chanudet <[email protected]>
Tested-by: Michael Ellerman <[email protected]> (powerpc)
Reviewed-by: Baoquan He <[email protected]>
Acked-by: Alexander Gordeev <[email protected]>
Acked-by: Mike Rapoport (IBM) <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Borislav Petkov (AMD) <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Nicholas Piggin <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

1 files changed, 0 insertions, 2 deletions

diff --git a/include/linux/memblock.h b/include/linux/memblock.h
index e2082240586d..40c62aca36ec 100644
--- a/include/linux/memblock.h
+++ b/include/linux/memblock.h
@@ -335,8 +335,6 @@ void __next_mem_pfn_range_in_zone(u64 *idx, struct zone *zone,
 	for (; i != U64_MAX;					  \
 	     __next_mem_pfn_range_in_zone(&i, zone, p_start, p_end))
 
-int __init deferred_page_init_max_threads(const struct cpumask *node_cpumask);
-
 #endif /* CONFIG_DEFERRED_STRUCT_PAGE_INIT */
 
 /**