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Date: Wed, 16 Dec 2020 14:43:54 +0100 From: Oscar Salvador <osalvador@...e.de> To: Muchun Song <songmuchun@...edance.com> Cc: 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, mhocko@...e.com, song.bao.hua@...ilicon.com, david@...hat.com, duanxiongchun@...edance.com, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org, linux-fsdevel@...r.kernel.org Subject: Re: [PATCH v9 09/11] mm/hugetlb: Introduce nr_free_vmemmap_pages in the struct hstate On Sun, Dec 13, 2020 at 11:45:32PM +0800, Muchun Song wrote: > All the infrastructure is ready, so we introduce 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 allocator. And initialize it "can be freed to buddy allocator" > in the hugetlb_vmemmap_init(). This patch is actual enablement of the > feature. > > Signed-off-by: Muchun Song <songmuchun@...edance.com> > Acked-by: Mike Kravetz <mike.kravetz@...cle.com> With below nits addressed you can add: Reviewed-by: Oscar Salvador <osalvador@...e.de> > static int __init early_hugetlb_free_vmemmap_param(char *buf) > { > + /* We cannot optimize if a "struct page" crosses page boundaries. */ > + if (!is_power_of_2(sizeof(struct page))) > + return 0; > + I wonder if we should report a warning in case someone wants to enable this feature and stuct page size it not power of 2. In case someone wonders why it does not work for him/her. > +void __init hugetlb_vmemmap_init(struct hstate *h) > +{ > + unsigned int nr_pages = pages_per_huge_page(h); > + unsigned int vmemmap_pages; > + > + if (!hugetlb_free_vmemmap_enabled) > + return; > + > + vmemmap_pages = (nr_pages * sizeof(struct page)) >> PAGE_SHIFT; > + /* > + * The head page and the first tail page are not to be freed to buddy > + * system, the others page will map to the first tail page. So there > + * are the remaining pages that can be freed. "the other pages will map to the first tail page, so they can be freed." > + * > + * Could RESERVE_VMEMMAP_NR be greater than @vmemmap_pages? It is true > + * on some architectures (e.g. aarch64). See Documentation/arm64/ > + * hugetlbpage.rst for more details. > + */ > + if (likely(vmemmap_pages > RESERVE_VMEMMAP_NR)) > + h->nr_free_vmemmap_pages = vmemmap_pages - RESERVE_VMEMMAP_NR; > + > + pr_info("can free %d vmemmap pages for %s\n", h->nr_free_vmemmap_pages, > + h->name); Maybe specify this is hugetlb code: pr_info("%s: blabla", __func__, ...) or pr_info("hugetlb: blalala", ...); although I am not sure whether we need that at all, or maybe just use pr_debug(). -- Oscar Salvador SUSE L3
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