From 5a74b9f1dc3d75635ca8918e53664d5d2ee0fff5 Mon Sep 17 00:00:00 2001 From: Kefeng Wang Date: Mon, 12 Jan 2026 23:09:52 +0800 Subject: [PATCH] mm: hugetlb: optimize replace_free_hugepage_folios() If no free hugepage folios are available, there is no need to perform any replacement operations. Additionally, gigantic folios should not be replaced under any circumstances. Therefore, we only check for the presence of non-gigantic folios, also adding the gigantic folio check to avoid accidental replacement. To optimize performance, we skip unnecessary iterations over pfn for compound pages and high-order buddy pages to save processing time. 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: 0m0.602s After: 0m0.431s [wangkefeng.wang@huawei.com: v2] Link: https://lkml.kernel.org/r/20260114135512.2159799-1-wangkefeng.wang@huawei.com [akpm@linux-foundation.org: use single-return-point style, tweak comment] Link: https://lkml.kernel.org/r/20260112150954.1802953-4-wangkefeng.wang@huawei.com Signed-off-by: Kefeng Wang Cc: Brendan Jackman Cc: David Hildenbrand Cc: Jane Chu Cc: Johannes Weiner Cc: Matthew Wilcox (Oracle) Cc: Muchun Song Cc: Oscar Salvador Cc: Sidhartha Kumar Cc: Vlastimil Babka Cc: Zi Yan Signed-off-by: Andrew Morton --- mm/hugetlb.c | 59 +++++++++++++++++++++++++++++++++++++++++++--------- 1 file changed, 49 insertions(+), 10 deletions(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 9c7efad6fa485..120ebd448b423 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -2810,23 +2810,62 @@ int isolate_or_dissolve_huge_folio(struct folio *folio, struct list_head *list) */ int replace_free_hugepage_folios(unsigned long start_pfn, unsigned long end_pfn) { - struct folio *folio; + unsigned long nr = 0; + struct page *page; + struct hstate *h; + LIST_HEAD(list); int ret = 0; - LIST_HEAD(isolate_list); + /* Avoid pfn iterations if no free non-gigantic huge pages */ + for_each_hstate(h) { + if (hstate_is_gigantic(h)) + continue; + + nr += h->free_huge_pages; + if (nr) + break; + } + + if (!nr) + return 0; while (start_pfn < end_pfn) { - folio = pfn_folio(start_pfn); + page = pfn_to_page(start_pfn); + nr = 1; - /* Not to disrupt normal path by vainly holding hugetlb_lock */ - if (folio_test_hugetlb(folio) && !folio_ref_count(folio)) { - ret = alloc_and_dissolve_hugetlb_folio(folio, &isolate_list); - if (ret) - break; + if (PageHuge(page) || PageCompound(page)) { + struct folio *folio = page_folio(page); + + nr = folio_nr_pages(folio) - folio_page_idx(folio, page); + + /* + * Don't disrupt normal path by vainly holding + * hugetlb_lock + */ + if (folio_test_hugetlb(folio) && !folio_ref_count(folio)) { + if (order_is_gigantic(folio_order(folio))) { + ret = -ENOMEM; + break; + } + + ret = alloc_and_dissolve_hugetlb_folio(folio, &list); + if (ret) + break; + + putback_movable_pages(&list); + } + } else if (PageBuddy(page)) { + /* + * Buddy order check without zone lock is unsafe and + * the order is maybe invalid, but race should be + * small, and the worst thing is skipping free hugetlb. + */ + const unsigned int order = buddy_order_unsafe(page); - putback_movable_pages(&isolate_list); + if (order <= MAX_PAGE_ORDER) + nr = 1UL << order; } - start_pfn++; + start_pfn += nr; } return ret; -- 2.47.3