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Sun, 24 Jan 2021 20:06:45 -0800 (PST) MIME-Version: 1.0 References: <20210117151053.24600-1-songmuchun@bytedance.com> <20210117151053.24600-3-songmuchun@bytedance.com> <472a58b9-12cb-3c3-d132-13dbae5174f0@google.com> In-Reply-To: <472a58b9-12cb-3c3-d132-13dbae5174f0@google.com> From: Muchun Song Date: Mon, 25 Jan 2021 12:06:09 +0800 Message-ID: Subject: Re: [External] Re: [PATCH v13 02/12] mm: hugetlb: introduce a new config HUGETLB_PAGE_FREE_VMEMMAP To: David Rientjes , Randy Dunlap Cc: Jonathan Corbet , Mike Kravetz , Thomas Gleixner , mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, dave.hansen@linux.intel.com, luto@kernel.org, Peter Zijlstra , viro@zeniv.linux.org.uk, Andrew Morton , paulmck@kernel.org, mchehab+huawei@kernel.org, pawan.kumar.gupta@linux.intel.com, oneukum@suse.com, anshuman.khandual@arm.com, jroedel@suse.de, Mina Almasry , Matthew Wilcox , Oscar Salvador , Michal Hocko , "Song Bao Hua (Barry Song)" , David Hildenbrand , =?UTF-8?B?SE9SSUdVQ0hJIE5BT1lBKOWggOWPoyDnm7TkuZ8p?= , Xiongchun duan , linux-doc@vger.kernel.org, LKML , Linux Memory Management List , linux-fsdevel Content-Type: text/plain; charset="UTF-8" X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Jan 25, 2021 at 7:58 AM David Rientjes wrote: > > > On Sun, 17 Jan 2021, Muchun Song wrote: > > > The HUGETLB_PAGE_FREE_VMEMMAP option is used to enable the freeing > > of unnecessary vmemmap associated with HugeTLB pages. The config > > option is introduced early so that supporting code can be written > > to depend on the option. The initial version of the code only > > provides support for x86-64. > > > > Like other code which frees vmemmap, this config option depends on > > HAVE_BOOTMEM_INFO_NODE. The routine register_page_bootmem_info() is > > used to register bootmem info. Therefore, make sure > > register_page_bootmem_info is enabled if HUGETLB_PAGE_FREE_VMEMMAP > > is defined. > > > > Signed-off-by: Muchun Song > > Reviewed-by: Oscar Salvador > > Acked-by: Mike Kravetz > > --- > > arch/x86/mm/init_64.c | 2 +- > > fs/Kconfig | 18 ++++++++++++++++++ > > 2 files changed, 19 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; > > > > for_each_online_node(i) > > diff --git a/fs/Kconfig b/fs/Kconfig > > index 976e8b9033c4..e7c4c2a79311 100644 > > --- a/fs/Kconfig > > +++ b/fs/Kconfig > > @@ -245,6 +245,24 @@ config HUGETLBFS > > config HUGETLB_PAGE > > def_bool HUGETLBFS > > > > +config HUGETLB_PAGE_FREE_VMEMMAP > > + def_bool HUGETLB_PAGE > > I'm not sure I understand the rationale for providing this help text if > this is def_bool depending on CONFIG_HUGETLB_PAGE. Are you intending that > this is actually configurable and we want to provide guidance to the admin > on when to disable it (which it currently doesn't)? If not, why have the > help text? This is __not__ configurable. Seems like a comment to help others understand this option. Like Randy said. Thanks. > > > + depends on X86_64 > > + depends on SPARSEMEM_VMEMMAP > > + depends on HAVE_BOOTMEM_INFO_NODE > > + help > > + The option HUGETLB_PAGE_FREE_VMEMMAP allows for the freeing of > > + some vmemmap pages associated with pre-allocated HugeTLB pages. > > + For example, on X86_64 6 vmemmap pages of size 4KB each can be > > + saved for each 2MB HugeTLB page. 4094 vmemmap pages of size 4KB > > + each can be saved for each 1GB HugeTLB page. > > + > > + When a HugeTLB page is allocated or freed, the vmemmap array > > + representing the range associated with the page will need to be > > + remapped. When a page is allocated, vmemmap pages are freed > > + after remapping. When a page is freed, previously discarded > > + vmemmap pages must be allocated before remapping. > > + > > config MEMFD_CREATE > > def_bool TMPFS || HUGETLBFS > >