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Date: Mon, 26 Oct 2020 22:50:59 +0800 From: Muchun Song <songmuchun@...edance.com> To: corbet@....net, mike.kravetz@...cle.com, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, x86@...nel.org, hpa@...or.com, dave.hansen@...ux.intel.com, luto@...nel.org, peterz@...radead.org, viro@...iv.linux.org.uk, akpm@...ux-foundation.org, paulmck@...nel.org, mchehab+huawei@...nel.org, pawan.kumar.gupta@...ux.intel.com, rdunlap@...radead.org, oneukum@...e.com, anshuman.khandual@....com, jroedel@...e.de, almasrymina@...gle.com, rientjes@...gle.com, willy@...radead.org Cc: duanxiongchun@...edance.com, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org, linux-fsdevel@...r.kernel.org, Muchun Song <songmuchun@...edance.com> Subject: [PATCH v2 04/19] mm/hugetlb: Introduce nr_free_vmemmap_pages in the struct hstate If the size of hugetlb page is 2MB, we need 512 struct page structures (8 pages) to be associated with it. As far as I know, we only use the first 4 struct page structures. For tail pages, the value of compound_dtor is the same. So we can reuse first page of tail page structs. We map the virtual addresses of the remaining 6 pages of tail page structs to the first tail page struct, and then free these 6 pages. Therefore, we need to reserve at least 2 pages as vmemmap areas. So we introduce a new nr_free_vmemmap_pages field in the hstate to indicate how many vmemmap pages associated with a hugetlb page that we can free to buddy system. Signed-off-by: Muchun Song <songmuchun@...edance.com> --- include/linux/hugetlb.h | 3 +++ mm/hugetlb.c | 35 +++++++++++++++++++++++++++++++++++ 2 files changed, 38 insertions(+) diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h index d5cc5f802dd4..eed3dd3bd626 100644 --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -492,6 +492,9 @@ struct hstate { unsigned int nr_huge_pages_node[MAX_NUMNODES]; unsigned int free_huge_pages_node[MAX_NUMNODES]; unsigned int surplus_huge_pages_node[MAX_NUMNODES]; +#ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP + unsigned int nr_free_vmemmap_pages; +#endif #ifdef CONFIG_CGROUP_HUGETLB /* cgroup control files */ struct cftype cgroup_files_dfl[7]; diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 81a41aa080a5..f1b2b733b49b 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -1292,6 +1292,39 @@ static inline void destroy_compound_gigantic_page(struct page *page, unsigned int order) { } #endif +#ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP +#define RESERVE_VMEMMAP_NR 2U + +static inline unsigned int nr_free_vmemmap(struct hstate *h) +{ + return h->nr_free_vmemmap_pages; +} + +static void __init hugetlb_vmemmap_init(struct hstate *h) +{ + unsigned int order = huge_page_order(h); + unsigned int vmemmap_pages; + + vmemmap_pages = ((1 << order) * sizeof(struct page)) >> PAGE_SHIFT; + /* + * The head page and the first tail page not free to buddy system, + * the others page will map to the first tail page. So there are + * (@vmemmap_pages - RESERVE_VMEMMAP_NR) pages can be freed. + */ + if (vmemmap_pages > RESERVE_VMEMMAP_NR) + h->nr_free_vmemmap_pages = vmemmap_pages - RESERVE_VMEMMAP_NR; + else + h->nr_free_vmemmap_pages = 0; + + pr_info("HugeTLB: can free %d vmemmap pages for %s\n", + h->nr_free_vmemmap_pages, h->name); +} +#else +static inline void hugetlb_vmemmap_init(struct hstate *h) +{ +} +#endif + static void update_and_free_page(struct hstate *h, struct page *page) { int i; @@ -3285,6 +3318,8 @@ void __init hugetlb_add_hstate(unsigned int order) snprintf(h->name, HSTATE_NAME_LEN, "hugepages-%lukB", huge_page_size(h)/1024); + hugetlb_vmemmap_init(h); + parsed_hstate = h; } -- 2.20.1
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