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Date: Mon, 7 Dec 2020 20:42:29 +0800 From: Muchun Song <songmuchun@...edance.com> To: David Hildenbrand <david@...hat.com> Cc: Jonathan Corbet <corbet@....net>, Mike Kravetz <mike.kravetz@...cle.com>, Thomas Gleixner <tglx@...utronix.de>, mingo@...hat.com, bp@...en8.de, x86@...nel.org, hpa@...or.com, dave.hansen@...ux.intel.com, luto@...nel.org, Peter Zijlstra <peterz@...radead.org>, viro@...iv.linux.org.uk, Andrew Morton <akpm@...ux-foundation.org>, paulmck@...nel.org, mchehab+huawei@...nel.org, pawan.kumar.gupta@...ux.intel.com, Randy Dunlap <rdunlap@...radead.org>, oneukum@...e.com, anshuman.khandual@....com, jroedel@...e.de, Mina Almasry <almasrymina@...gle.com>, David Rientjes <rientjes@...gle.com>, Matthew Wilcox <willy@...radead.org>, Oscar Salvador <osalvador@...e.de>, Michal Hocko <mhocko@...e.com>, "Song Bao Hua (Barry Song)" <song.bao.hua@...ilicon.com>, Xiongchun duan <duanxiongchun@...edance.com>, linux-doc@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>, Linux Memory Management List <linux-mm@...ck.org>, linux-fsdevel <linux-fsdevel@...r.kernel.org> Subject: Re: [External] Re: [PATCH v7 03/15] mm/hugetlb: Introduce a new config HUGETLB_PAGE_FREE_VMEMMAP On Mon, Dec 7, 2020 at 8:19 PM David Hildenbrand <david@...hat.com> wrote: > > On 30.11.20 16:18, Muchun Song wrote: > > The purpose of introducing HUGETLB_PAGE_FREE_VMEMMAP is to configure > > whether to enable the feature of freeing unused vmemmap associated > > with HugeTLB pages. And this is just for dependency check. Now only > > support x86. > > x86 - i386 and x86-64? (I assume the latter only ;) ) Yeah, you are right. Only the latter support SPARSEMEM_VMEMMAP. > > > > > Signed-off-by: Muchun Song <songmuchun@...edance.com> > > --- > > arch/x86/mm/init_64.c | 2 +- > > fs/Kconfig | 14 ++++++++++++++ > > 2 files changed, 15 insertions(+), 1 deletion(-) > > > > diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c > > index 0a45f062826e..0435bee2e172 100644 > > --- a/arch/x86/mm/init_64.c > > +++ b/arch/x86/mm/init_64.c > > @@ -1225,7 +1225,7 @@ static struct kcore_list kcore_vsyscall; > > > > static void __init register_page_bootmem_info(void) > > { > > -#ifdef CONFIG_NUMA > > +#if defined(CONFIG_NUMA) || defined(CONFIG_HUGETLB_PAGE_FREE_VMEMMAP) > > int i; > > > > Why does this hunk belong into this patch? Looks like this should go > into another patch. Of course can. But Mike suggests that it is better to use it when introducing a new config. Because this config depends on HAVE_BOOTMEM_INFO_NODE. And register_page_bootmem_info is aimed to register bootmem info. So maybe it is reasonable from this point of view. What is your opinion? > > > for_each_online_node(i) > > diff --git a/fs/Kconfig b/fs/Kconfig > > index 976e8b9033c4..4961dd488444 100644 > > --- a/fs/Kconfig > > +++ b/fs/Kconfig > > @@ -245,6 +245,20 @@ config HUGETLBFS > > config HUGETLB_PAGE > > def_bool HUGETLBFS > > > > +config HUGETLB_PAGE_FREE_VMEMMAP > > + def_bool HUGETLB_PAGE > > + depends on X86 > > + depends on SPARSEMEM_VMEMMAP > > + depends on HAVE_BOOTMEM_INFO_NODE > > + help > > + When using HUGETLB_PAGE_FREE_VMEMMAP, the system can save up some > > + memory from pre-allocated HugeTLB pages when they are not used. > > + 6 pages per 2MB HugeTLB page and 4094 per 1GB HugeTLB page. > > Calculations only apply to 4k base pages, no? No, if the base page is not 4k, we also can free 6 pages. For example: If the base page size is 64k, the PMD huge page size is 512MB. We also can free 6 pages(64k * 6) vmemmap. But maybe I should document this. Thanks. > (maybe generalize this a > bit or mention 4k base pages - I'm pretty sure we'll see the "depends on > X86" part fairly soon if this goes upstream) Yeah, it can be easy to adapt to different architectures. :) > > > -- > Thanks, > > David / dhildenb > -- Yours, Muchun
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