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Message-ID: <0ca35fe5-9799-4518-9fb1-701c88501a8d@redhat.com>
Date: Sat, 21 Dec 2024 15:35:10 +0100
From: David Hildenbrand <david@...hat.com>
To: yangge1116@....com, akpm@...ux-foundation.org
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org, stable@...r.kernel.org,
21cnbao@...il.com, baolin.wang@...ux.alibaba.com, muchun.song@...ux.dev,
liuzixing@...on.cn
Subject: Re: [PATCH] replace free hugepage folios after migration
On 18.12.24 07:33, yangge1116@....com wrote:
> From: yangge <yangge1116@....com>
>
> My machine has 4 NUMA nodes, each equipped with 32GB of memory. I
> have configured each NUMA node with 16GB of CMA and 16GB of in-use
> hugetlb pages. The allocation of contiguous memory via the
> cma_alloc() function can fail probabilistically.
>
> The cma_alloc() function may fail if it sees an in-use hugetlb page
> within the allocation range, even if that page has already been
> migrated. When in-use hugetlb pages are migrated, they may simply
> be released back into the free hugepage pool instead of being
> returned to the buddy system. This can cause the
> test_pages_isolated() function check to fail, ultimately leading
> to the failure of the cma_alloc() function:
> cma_alloc()
> __alloc_contig_migrate_range() // migrate in-use hugepage
> test_pages_isolated()
> __test_page_isolated_in_pageblock()
> PageBuddy(page) // check if the page is in buddy
>
> To address this issue, we will add a function named
> replace_free_hugepage_folios(). This function will replace the
> hugepage in the free hugepage pool with a new one and release the
> old one to the buddy system. After the migration of in-use hugetlb
> pages is completed, we will invoke the replace_free_hugepage_folios()
> function to ensure that these hugepages are properly released to
> the buddy system. Following this step, when the test_pages_isolated()
> function is executed for inspection, it will successfully pass.
>
> Signed-off-by: yangge <yangge1116@....com>
> ---
> include/linux/hugetlb.h | 6 ++++++
> mm/hugetlb.c | 37 +++++++++++++++++++++++++++++++++++++
> mm/page_alloc.c | 13 ++++++++++++-
> 3 files changed, 55 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index ae4fe86..7d36ac8 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -681,6 +681,7 @@ struct huge_bootmem_page {
> };
>
> int isolate_or_dissolve_huge_page(struct page *page, struct list_head *list);
> +int replace_free_hugepage_folios(unsigned long start_pfn, unsigned long end_pfn);
> struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
> unsigned long addr, int avoid_reserve);
> struct folio *alloc_hugetlb_folio_nodemask(struct hstate *h, int preferred_nid,
> @@ -1059,6 +1060,11 @@ static inline int isolate_or_dissolve_huge_page(struct page *page,
> return -ENOMEM;
> }
>
> +int replace_free_hugepage_folios(unsigned long start_pfn, unsigned long end_pfn)
> +{
> + return 0;
> +}
> +
> static inline struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
> unsigned long addr,
> int avoid_reserve)
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 8e1db80..a099c54 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -2975,6 +2975,43 @@ int isolate_or_dissolve_huge_page(struct page *page, struct list_head *list)
> return ret;
> }
>
> +/*
> + * replace_free_hugepage_folios - Replace free hugepage folios in a given pfn
> + * range with new folios.
> + * @stat_pfn: start pfn of the given pfn range
> + * @end_pfn: end pfn of the given pfn range
> + * Returns 0 on success, otherwise negated error.
> + */
> +int replace_free_hugepage_folios(unsigned long start_pfn, unsigned long end_pfn)
> +{
> + struct hstate *h;
> + struct folio *folio;
> + int ret = 0;
> +
> + LIST_HEAD(isolate_list);
> +
> + while (start_pfn < end_pfn) {
> + folio = pfn_folio(start_pfn);
> + if (folio_test_hugetlb(folio)) {
> + h = folio_hstate(folio);
> + } else {
> + start_pfn++;
> + continue;
> + }
> +
> + if (!folio_ref_count(folio)) {
> + ret = alloc_and_dissolve_hugetlb_folio(h, folio, &isolate_list);
> + if (ret)
> + break;
> +
> + putback_movable_pages(&isolate_list);
> + }
> + start_pfn++;
> + }
> +
> + return ret;
> +}
> +
> struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
> unsigned long addr, int avoid_reserve)
> {
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index dde19db..1dcea28 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -6504,7 +6504,18 @@ int alloc_contig_range_noprof(unsigned long start, unsigned long end,
> ret = __alloc_contig_migrate_range(&cc, start, end, migratetype);
> if (ret && ret != -EBUSY)
> goto done;
> - ret = 0;
> +
> + /*
> + * When in-use hugetlb pages are migrated, they may simply be
> + * released back into the free hugepage pool instead of being
> + * returned to the buddy system. After the migration of in-use
> + * huge pages is completed, we will invoke the
> + * replace_free_hugepage_folios() function to ensure that
> + * these hugepages are properly released to the buddy system.
> + */
As mentioned in my other mail, what I don't like about this is, IIUC,
the pages can get reallocated anytime after we successfully migrated
them, or is there anything that prevents that?
Did you ever try allocating a larger range with a single
alloc_contig_range() call, that possibly has to migrate multiple hugetlb
folios in one go (and maybe just allocates one of the just-freed hugetlb
folios as migration target)?
--
Cheers,
David / dhildenb
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