[PATCH v8 02/12] mm/hugetlb: Introduce a new config HUGETLB_PAGE_FREE_VMEMMAP

Muchun Song
2020-12-10T03:59:37Z

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
x86-64.

Because this config depends on HAVE_BOOTMEM_INFO_NODE. And the function
of the register_page_bootmem_info() is aimed to register bootmem info.
So we should register bootmem info when this config is enabled.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
arch/x86/mm/init_64.c | 2 +-
fs/Kconfig | 15 +++++++++++++++
2 files changed, 16 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..4c3a9c614983 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -245,6 +245,21 @@ config HUGETLBFS
config HUGETLB_PAGE
def_bool HUGETLBFS

+config HUGETLB_PAGE_FREE_VMEMMAP
+ def_bool HUGETLB_PAGE
+ depends on X86_64
+ 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 HugeTLB page of the pmd level mapping and (PAGE_SIZE - 2)
+ pages per HugeTLB page of the pud level mapping.
+
+ When the pages are going to be used or freed up, the vmemmap array
+ representing that range needs to be remapped again and the pages
+ we discarded earlier need to be rellocated again.
+
config MEMFD_CREATE
def_bool TMPFS || HUGETLBFS

--
2.11.0