Re: [PATCH 2/5] mm: page_alloc: optimize pfn_range_valid_contig()

[Andrew Morton <akpm@linux-foundation.org>]

On Tue, 13 Jan 2026 17:55:43 +0800 Kefeng Wang <wangkefeng.wang@huawei.com> wrote:

> 
> > 
> > With the changes to the commit message, feel free to add
> 
> OK, I will update it.

akpmbot already did that.

> > 
> > Reviewed-by: Zi Yan <ziy@nvidia.com>

Thanks both.



From: Kefeng Wang <wangkefeng.wang@huawei.com>
Subject: mm: page_alloc: optimize pfn_range_valid_contig()
Date: Mon, 12 Jan 2026 23:09:51 +0800

The alloc_contig_pages() spends a significant amount of time within
pfn_range_valid_contig().

- set_max_huge_pages
   - 99.98% alloc_pool_huge_folio
        only_alloc_fresh_hugetlb_folio.isra.0
      - alloc_contig_frozen_pages_noprof
         - 87.00% pfn_range_valid_contig
              pfn_to_online_page
         - 12.91% alloc_contig_frozen_range_noprof
              4.51% replace_free_hugepage_folios
            - 4.02% prep_new_page
                 prep_compound_page
            - 2.98% undo_isolate_page_range
               - 2.79% unset_migratetype_isolate
                  - 2.75% __move_freepages_block_isolate
                       2.71% __move_freepages_block
            - 0.98% start_isolate_page_range
                 0.66% set_migratetype_isolate

To optimize this process, use the new helper page_is_unmovable() to avoid
more unnecessary iterations for compound pages, such as THP not on LRU,
and high-order buddy pages, which significantly improving the efficiency
of contiguous memory allocation.

A simple test on machine with 114G free memory, allocate 120 * 1G
HugeTLB folios(104 successfully returned),

  time echo 120 > /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages

Before: 0m3.605s
After:  0m0.602s

Link: https://lkml.kernel.org/r/20260112150954.1802953-3-wangkefeng.wang@huawei.com
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jane Chu <jane.chu@oracle.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/page_alloc.c |   25 ++++++++-----------------
 1 file changed, 8 insertions(+), 17 deletions(-)

--- a/mm/page_alloc.c~mm-page_alloc-optimize-pfn_range_valid_contig
+++ a/mm/page_alloc.c
@@ -7157,18 +7157,20 @@ static bool pfn_range_valid_contig(struc
 				   unsigned long nr_pages, bool skip_hugetlb,
 				   bool *skipped_hugetlb)
 {
-	unsigned long i, end_pfn = start_pfn + nr_pages;
+	unsigned long end_pfn = start_pfn + nr_pages;
 	struct page *page;
 
-	for (i = start_pfn; i < end_pfn; i++) {
-		page = pfn_to_online_page(i);
+	while (start_pfn < end_pfn) {
+		unsigned long step = 1;
+
+		page = pfn_to_online_page(start_pfn);
 		if (!page)
 			return false;
 
 		if (page_zone(page) != z)
 			return false;
 
-		if (PageReserved(page))
+		if (page_is_unmovable(z, page, PB_ISOLATE_MODE_OTHER, &step))
 			return false;
 
 		/*
@@ -7183,9 +7185,6 @@ static bool pfn_range_valid_contig(struc
 		if (PageHuge(page)) {
 			unsigned int order;
 
-			if (!IS_ENABLED(CONFIG_ARCH_ENABLE_HUGEPAGE_MIGRATION))
-				return false;
-
 			if (skip_hugetlb) {
 				*skipped_hugetlb = true;
 				return false;
@@ -7196,17 +7195,9 @@ static bool pfn_range_valid_contig(struc
 			if ((order >= MAX_FOLIO_ORDER) ||
 			    (nr_pages <= (1 << order)))
 				return false;
-
-			/*
-			 * Reaching this point means we've encounted a huge page
-			 * smaller than nr_pages, skip all pfn's for that page.
-			 *
-			 * We can't get here from a tail-PageHuge, as it implies
-			 * we started a scan in the middle of a hugepage larger
-			 * than nr_pages - which the prior check filters for.
-			 */
-			i += (1 << order) - 1;
 		}
+
+		start_pfn += step;
 	}
 	return true;
 }
_