mm: hugetlb: log time needed to allocate hugepages

Having this information allows users to easily tune the
hugepages_node_threads parameter.

Link: https://lkml.kernel.org/r/20250227-hugepage-parameter-v2-3-7db8c6dc0453@cyberus-technology.de
Signed-off-by: Thomas Prescher <thomas.prescher@cyberus-technology.de>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: tpressure

mm/hugetlb.c

@@ -3608,6 +3608,9 @@ static unsigned long __init hugetlb_pages_alloc_boot(struct hstate *h)
 		.numa_aware	= true
 	};
 
+	unsigned long jiffies_start;
+	unsigned long jiffies_end;
+
 	job.thread_fn	= hugetlb_pages_alloc_boot_node;
 	job.start	= 0;
 	job.size	= h->max_huge_pages;
@@ -3635,7 +3638,14 @@ static unsigned long __init hugetlb_pages_alloc_boot(struct hstate *h)
 
 	job.max_threads	= hugepage_allocation_threads;
 	job.min_chunk	= h->max_huge_pages / hugepage_allocation_threads;
+
+	jiffies_start = jiffies;
 	padata_do_multithreaded(&job);
+	jiffies_end = jiffies;
+
+	pr_info("HugeTLB: allocation took %dms with hugepage_allocation_threads=%ld\n",
+		jiffies_to_msecs(jiffies_end - jiffies_start),
+		hugepage_allocation_threads);
 
 	return h->nr_huge_pages;
 }