Re: [PATCH v2 3/5] mm: hugetlb: optimize replace_free_hugepage_folios()

[Kefeng Wang <wangkefeng.wang@huawei.com>]

On 2026/1/16 6:42, Andrew Morton wrote:
> On Wed, 14 Jan 2026 21:55:12 +0800 Kefeng Wang <wangkefeng.wang@huawei.com> wrote:
> 
>> 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
>>
> 
> Thanks, I'll queue this as a -fix, below.
> 
> nit: the function has become rather a jumble of bailout styles:
> 
> :				if (order_is_gigantic(folio_order(folio)))
> : 					return -ENOMEM;
> 
> This could have done ret=-ENOMEM;break;
> 
> :
> : 				ret = alloc_and_dissolve_hugetlb_folio(folio, &list);
> : 				if (ret)
> : 					break;
> 
> While this could have done `return ret;'!
> 
> Single-return-point is preferred style, I think.  Mainly to help avoid
> leakage of resources and locks as the code evolves.
> 
> How does this look on top?

Hi Andrew, I'm fine with it, thanks your for the update.

> 
> From: Andrew Morton <akpm@linux-foundation.org>
> Subject: mm-hugetlb-optimize-replace_free_hugepage_folios-v2-fix
> Date: Thu Jan 15 02:34:07 PM PST 2026
> 
> use single-return-point style, tweak comment
> 
> Cc: Kefeng Wang <wangkefeng.wang@huawei.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: Oscar Salvador <osalvador@suse.de>
> Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Cc: Zi Yan <ziy@nvidia.com>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
> 
>   mm/hugetlb.c |   11 ++++++++---
>   1 file changed, 8 insertions(+), 3 deletions(-)
> 
> --- a/mm/hugetlb.c~mm-hugetlb-optimize-replace_free_hugepage_folios-v2-fix
> +++ a/mm/hugetlb.c
> @@ -2834,10 +2834,15 @@ int replace_free_hugepage_folios(unsigne
>   
>   			nr = folio_nr_pages(folio) - folio_page_idx(folio, page);
>   
> -			/* Not to disrupt normal path by vainly holding hugetlb_lock */
> +			/*
> +			 * 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)))
> -					return -ENOMEM;
> +				if (order_is_gigantic(folio_order(folio))) {
> +					ret = -ENOMEM;
> +					break;
> +				}
>   
>   				ret = alloc_and_dissolve_hugetlb_folio(folio, &list);
>   				if (ret)
> _
> 
> 
> 
> 
> 
> 
> From: Kefeng Wang <wangkefeng.wang@huawei.com>
> Subject: mm: hugetlb: optimize replace_free_hugepage_folios()
> Date: Wed, 14 Jan 2026 21:55:12 +0800
> 
> Turn back to use alloc_and_dissolve_hugetlb_folio() since Oscar pointed
> out that the return value is different.  Then adding gigantic folio check
> independently, also update changelog.
> 
> Link: https://lkml.kernel.org/r/20260114135512.2159799-1-wangkefeng.wang@huawei.com
> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.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: Oscar Salvador <osalvador@suse.de>
> Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Cc: Zi Yan <ziy@nvidia.com>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
> 
>   mm/hugetlb.c |   10 +++++++---
>   1 file changed, 7 insertions(+), 3 deletions(-)
> 
> --- a/mm/hugetlb.c~mm-hugetlb-optimize-replace_free_hugepage_folios-v2
> +++ a/mm/hugetlb.c
> @@ -2810,6 +2810,7 @@ int replace_free_hugepage_folios(unsigne
>   	struct page *page;
>   	struct hstate *h;
>   	LIST_HEAD(list);
> +	int ret = 0;
>   
>   	/* Avoid pfn iterations if no free non-gigantic huge pages */
>   	for_each_hstate(h) {
> @@ -2835,9 +2836,13 @@ int replace_free_hugepage_folios(unsigne
>   
>   			/* Not to disrupt normal path by vainly holding hugetlb_lock */
>   			if (folio_test_hugetlb(folio) && !folio_ref_count(folio)) {
> -				if (isolate_or_dissolve_huge_folio(folio, &list))
> +				if (order_is_gigantic(folio_order(folio)))
>   					return -ENOMEM;
>   
> +				ret = alloc_and_dissolve_hugetlb_folio(folio, &list);
> +				if (ret)
> +					break;
> +
>   				putback_movable_pages(&list);
>   			}
>   		} else if (PageBuddy(page)) {
> @@ -2851,11 +2856,10 @@ int replace_free_hugepage_folios(unsigne
>   			if (order <= MAX_PAGE_ORDER)
>   				nr = 1UL << order;
>   		}
> -
>   		start_pfn += nr;
>   	}
>   
> -	return 0;
> +	return ret;
>   }
>   
>   void wait_for_freed_hugetlb_folios(void)
> _
> 
>