hugetlb: add __read_mostly to sysctl_hugetlb_shm_group

sysctl bits are mostly-read values.

Link: https://lkml.kernel.org/r/20251121194859.265259-2-gourry@gourry.net
Signed-off-by: Gregory Price <gourry@gourry.net>
Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Oscar Salvador <osalvador@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: Gregory Price

include/linux/hugetlb.h

@@ -171,7 +171,7 @@ bool hugetlbfs_pagecache_present(struct hstate *h,
 
 struct address_space *hugetlb_folio_mapping_lock_write(struct folio *folio);
 
-extern int sysctl_hugetlb_shm_group;
+extern int sysctl_hugetlb_shm_group __read_mostly;
 extern struct list_head huge_boot_pages[MAX_NUMNODES];
 
 void hugetlb_bootmem_alloc(void);