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mm: backport mm_init.c to bring init_reserved_page optimisations

Eric Chanudet requested to merge echanude/centos-stream-9:early_pfn_to_nid into main

JIRA: https://issues.redhat.com/browse/RHEL-36126

Bring a DEFERRED_STRUCT_PAGE_INIT optimisations ([1]) to improve boot times for the automotive use-case.

The following path is improved by avoiding to take the lock when not necessary:

-> reserve_bootmem_region  
 -> init_reserved_page  
  -> early_pfn_to_nid  
   -> spin_lock(&early_pfn_lock)  
    -> __early_pfn_to_nid  
     -> memblock_search_pfn_nid()  
      -> memblock_search()  
   -> spin_unlock(&early_pfn_lock)

On sa8775p-ride (using automotive configuration), this saves ~30ms before time_init() is called, which makes it hard to observe.

Signed-off-by: Eric Chanudet echanude@redhat.com

Edited by Eric Chanudet

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