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Message-ID: <9a716de0-91c3-5f29-4f88-391b9aaeb5ce@linux.dev>
Date: Tue, 19 Sep 2023 14:09:25 +0800
From: Muchun Song <muchun.song@...ux.dev>
To: Mike Kravetz <mike.kravetz@...cle.com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Cc: Muchun Song <songmuchun@...edance.com>,
Joao Martins <joao.m.martins@...cle.com>,
Oscar Salvador <osalvador@...e.de>,
David Hildenbrand <david@...hat.com>,
Miaohe Lin <linmiaohe@...wei.com>,
David Rientjes <rientjes@...gle.com>,
Anshuman Khandual <anshuman.khandual@....com>,
Naoya Horiguchi <naoya.horiguchi@...ux.dev>,
Barry Song <21cnbao@...il.com>, Michal Hocko <mhocko@...e.com>,
Matthew Wilcox <willy@...radead.org>,
Xiongchun Duan <duanxiongchun@...edance.com>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v4 5/8] hugetlb: batch freeing of vmemmap pages
On 2023/9/19 07:01, Mike Kravetz wrote:
> Now that batching of hugetlb vmemmap optimization processing is possible,
> batch the freeing of vmemmap pages. When freeing vmemmap pages for a
> hugetlb page, we add them to a list that is freed after the entire batch
> has been processed.
>
> This enhances the ability to return contiguous ranges of memory to the
> low level allocators.
>
> Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>
Reviewed-by: Muchun Song <songmuchun@...edance.com>
One nit bellow.
> ---
> mm/hugetlb_vmemmap.c | 85 ++++++++++++++++++++++++++++++--------------
> 1 file changed, 59 insertions(+), 26 deletions(-)
>
> diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
> index 463a4037ec6e..147ed15bcae4 100644
> --- a/mm/hugetlb_vmemmap.c
> +++ b/mm/hugetlb_vmemmap.c
> @@ -222,6 +222,9 @@ static void free_vmemmap_page_list(struct list_head *list)
> {
> struct page *page, *next;
>
> + if (list_empty(list))
> + return;
It seems unnecessary since the following "list_for_each_entry_safe"
could handle empty-list case. Right?
> +
> list_for_each_entry_safe(page, next, list, lru)
> free_vmemmap_page(page);
> }
> @@ -251,7 +254,7 @@ static void vmemmap_remap_pte(pte_t *pte, unsigned long addr,
> }
>
> entry = mk_pte(walk->reuse_page, pgprot);
> - list_add_tail(&page->lru, walk->vmemmap_pages);
> + list_add(&page->lru, walk->vmemmap_pages);
> set_pte_at(&init_mm, addr, pte, entry);
> }
>
> @@ -306,18 +309,20 @@ static void vmemmap_restore_pte(pte_t *pte, unsigned long addr,
> * @end: end address of the vmemmap virtual address range that we want to
> * remap.
> * @reuse: reuse address.
> + * @vmemmap_pages: list to deposit vmemmap pages to be freed. It is callers
> + * responsibility to free pages.
> *
> * Return: %0 on success, negative error code otherwise.
> */
> static int vmemmap_remap_free(unsigned long start, unsigned long end,
> - unsigned long reuse)
> + unsigned long reuse,
> + struct list_head *vmemmap_pages)
> {
> int ret;
> - LIST_HEAD(vmemmap_pages);
> struct vmemmap_remap_walk walk = {
> .remap_pte = vmemmap_remap_pte,
> .reuse_addr = reuse,
> - .vmemmap_pages = &vmemmap_pages,
> + .vmemmap_pages = vmemmap_pages,
> };
> int nid = page_to_nid((struct page *)reuse);
> gfp_t gfp_mask = GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN;
> @@ -334,7 +339,7 @@ static int vmemmap_remap_free(unsigned long start, unsigned long end,
> if (walk.reuse_page) {
> copy_page(page_to_virt(walk.reuse_page),
> (void *)walk.reuse_addr);
> - list_add(&walk.reuse_page->lru, &vmemmap_pages);
> + list_add(&walk.reuse_page->lru, vmemmap_pages);
> }
>
> /*
> @@ -365,15 +370,13 @@ static int vmemmap_remap_free(unsigned long start, unsigned long end,
> walk = (struct vmemmap_remap_walk) {
> .remap_pte = vmemmap_restore_pte,
> .reuse_addr = reuse,
> - .vmemmap_pages = &vmemmap_pages,
> + .vmemmap_pages = vmemmap_pages,
> };
>
> vmemmap_remap_range(reuse, end, &walk);
> }
> mmap_read_unlock(&init_mm);
>
> - free_vmemmap_page_list(&vmemmap_pages);
> -
> return ret;
> }
>
> @@ -389,7 +392,7 @@ static int alloc_vmemmap_page_list(unsigned long start, unsigned long end,
> page = alloc_pages_node(nid, gfp_mask, 0);
> if (!page)
> goto out;
> - list_add_tail(&page->lru, list);
> + list_add(&page->lru, list);
> }
>
> return 0;
> @@ -576,24 +579,17 @@ static bool vmemmap_should_optimize(const struct hstate *h, const struct page *h
> return true;
> }
>
> -/**
> - * hugetlb_vmemmap_optimize - optimize @head page's vmemmap pages.
> - * @h: struct hstate.
> - * @head: the head page whose vmemmap pages will be optimized.
> - *
> - * This function only tries to optimize @head's vmemmap pages and does not
> - * guarantee that the optimization will succeed after it returns. The caller
> - * can use HPageVmemmapOptimized(@head) to detect if @head's vmemmap pages
> - * have been optimized.
> - */
> -void hugetlb_vmemmap_optimize(const struct hstate *h, struct page *head)
> +static int __hugetlb_vmemmap_optimize(const struct hstate *h,
> + struct page *head,
> + struct list_head *vmemmap_pages)
> {
> + int ret = 0;
> unsigned long vmemmap_start = (unsigned long)head, vmemmap_end;
> unsigned long vmemmap_reuse;
>
> VM_WARN_ON_ONCE(!PageHuge(head));
> if (!vmemmap_should_optimize(h, head))
> - return;
> + return ret;
>
> static_branch_inc(&hugetlb_optimize_vmemmap_key);
>
> @@ -603,21 +599,58 @@ void hugetlb_vmemmap_optimize(const struct hstate *h, struct page *head)
>
> /*
> * Remap the vmemmap virtual address range [@vmemmap_start, @vmemmap_end)
> - * to the page which @vmemmap_reuse is mapped to, then free the pages
> - * which the range [@vmemmap_start, @vmemmap_end] is mapped to.
> + * to the page which @vmemmap_reuse is mapped to. Add pages previously
> + * mapping the range to vmemmap_pages list so that they can be freed by
> + * the caller.
> */
> - if (vmemmap_remap_free(vmemmap_start, vmemmap_end, vmemmap_reuse))
> + ret = vmemmap_remap_free(vmemmap_start, vmemmap_end, vmemmap_reuse, vmemmap_pages);
> + if (ret)
> static_branch_dec(&hugetlb_optimize_vmemmap_key);
> else
> SetHPageVmemmapOptimized(head);
> +
> + return ret;
> +}
> +
> +/**
> + * hugetlb_vmemmap_optimize - optimize @head page's vmemmap pages.
> + * @h: struct hstate.
> + * @head: the head page whose vmemmap pages will be optimized.
> + *
> + * This function only tries to optimize @head's vmemmap pages and does not
> + * guarantee that the optimization will succeed after it returns. The caller
> + * can use HPageVmemmapOptimized(@head) to detect if @head's vmemmap pages
> + * have been optimized.
> + */
> +void hugetlb_vmemmap_optimize(const struct hstate *h, struct page *head)
> +{
> + LIST_HEAD(vmemmap_pages);
> +
> + __hugetlb_vmemmap_optimize(h, head, &vmemmap_pages);
> + free_vmemmap_page_list(&vmemmap_pages);
> }
>
> void hugetlb_vmemmap_optimize_folios(struct hstate *h, struct list_head *folio_list)
> {
> struct folio *folio;
> + LIST_HEAD(vmemmap_pages);
>
> - list_for_each_entry(folio, folio_list, lru)
> - hugetlb_vmemmap_optimize(h, &folio->page);
> + list_for_each_entry(folio, folio_list, lru) {
> + int ret = __hugetlb_vmemmap_optimize(h, &folio->page,
> + &vmemmap_pages);
> +
> + /*
> + * Pages to be freed may have been accumulated. If we
> + * encounter an ENOMEM, free what we have and try again.
> + */
> + if (ret == -ENOMEM && !list_empty(&vmemmap_pages)) {
> + free_vmemmap_page_list(&vmemmap_pages);
> + INIT_LIST_HEAD(&vmemmap_pages);
> + __hugetlb_vmemmap_optimize(h, &folio->page, &vmemmap_pages);
> + }
> + }
> +
> + free_vmemmap_page_list(&vmemmap_pages);
> }
>
> static struct ctl_table hugetlb_vmemmap_sysctls[] = {
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