From: Muchun Song <songmuchun@xxxxxxxxxxxxx> Subject: mm: hugetlb: add a kernel parameter hugetlb_free_vmemmap Add a kernel parameter hugetlb_free_vmemmap to enable the feature of freeing unused vmemmap pages associated with each hugetlb page on boot. We disable PMD mapping of vmemmap pages for x86-64 arch when this feature is enabled. Because vmemmap_remap_free() depends on vmemmap being base page mapped. Link: https://lkml.kernel.org/r/20210510030027.56044-8-songmuchun@xxxxxxxxxxxxx Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx> Reviewed-by: Oscar Salvador <osalvador@xxxxxxx> Reviewed-by: Barry Song <song.bao.hua@xxxxxxxxxxxxx> Reviewed-by: Miaohe Lin <linmiaohe@xxxxxxxxxx> Tested-by: Chen Huang <chenhuang5@xxxxxxxxxx> Tested-by: Bodeddula Balasubramaniam <bodeddub@xxxxxxxxxx> Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx> Cc: Andy Lutomirski <luto@xxxxxxxxxx> Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx> Cc: Balbir Singh <bsingharora@xxxxxxxxx> Cc: Borislav Petkov <bp@xxxxxxxxx> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> Cc: David Hildenbrand <david@xxxxxxxxxx> Cc: David Rientjes <rientjes@xxxxxxxxxx> Cc: HORIGUCHI NAOYA <naoya.horiguchi@xxxxxxx> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Joao Martins <joao.m.martins@xxxxxxxxxx> Cc: Joerg Roedel <jroedel@xxxxxxx> Cc: Jonathan Corbet <corbet@xxxxxxx> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxx> Cc: Mina Almasry <almasrymina@xxxxxxxxxx> Cc: Oliver Neukum <oneukum@xxxxxxxx> Cc: Paul E. McKenney <paulmck@xxxxxxxxxx> Cc: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Xiongchun Duan <duanxiongchun@xxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- Documentation/admin-guide/kernel-parameters.txt | 17 +++++++++ Documentation/admin-guide/mm/hugetlbpage.rst | 3 + arch/x86/mm/init_64.c | 8 +++- include/linux/hugetlb.h | 19 +++++++++++ mm/hugetlb_vmemmap.c | 24 ++++++++++++++ 5 files changed, 69 insertions(+), 2 deletions(-) --- a/arch/x86/mm/init_64.c~mm-hugetlb-add-a-kernel-parameter-hugetlb_free_vmemmap +++ a/arch/x86/mm/init_64.c @@ -34,6 +34,7 @@ #include <linux/gfp.h> #include <linux/kcore.h> #include <linux/bootmem_info.h> +#include <linux/hugetlb.h> #include <asm/processor.h> #include <asm/bios_ebda.h> @@ -1609,7 +1610,8 @@ int __meminit vmemmap_populate(unsigned VM_BUG_ON(!IS_ALIGNED(start, PAGE_SIZE)); VM_BUG_ON(!IS_ALIGNED(end, PAGE_SIZE)); - if (end - start < PAGES_PER_SECTION * sizeof(struct page)) + if ((is_hugetlb_free_vmemmap_enabled() && !altmap) || + end - start < PAGES_PER_SECTION * sizeof(struct page)) err = vmemmap_populate_basepages(start, end, node, NULL); else if (boot_cpu_has(X86_FEATURE_PSE)) err = vmemmap_populate_hugepages(start, end, node, altmap); @@ -1637,6 +1639,8 @@ void register_page_bootmem_memmap(unsign pmd_t *pmd; unsigned int nr_pmd_pages; struct page *page; + bool base_mapping = !boot_cpu_has(X86_FEATURE_PSE) || + is_hugetlb_free_vmemmap_enabled(); for (; addr < end; addr = next) { pte_t *pte = NULL; @@ -1662,7 +1666,7 @@ void register_page_bootmem_memmap(unsign } get_page_bootmem(section_nr, pud_page(*pud), MIX_SECTION_INFO); - if (!boot_cpu_has(X86_FEATURE_PSE)) { + if (base_mapping) { next = (addr + PAGE_SIZE) & PAGE_MASK; pmd = pmd_offset(pud, addr); if (pmd_none(*pmd)) --- a/Documentation/admin-guide/kernel-parameters.txt~mm-hugetlb-add-a-kernel-parameter-hugetlb_free_vmemmap +++ a/Documentation/admin-guide/kernel-parameters.txt @@ -1567,6 +1567,23 @@ Documentation/admin-guide/mm/hugetlbpage.rst. Format: size[KMG] + hugetlb_free_vmemmap= + [KNL] Reguires CONFIG_HUGETLB_PAGE_FREE_VMEMMAP + enabled. + Allows heavy hugetlb users to free up some more + memory (6 * PAGE_SIZE for each 2MB hugetlb page). + This feauture is not free though. Large page + tables are not used to back vmemmap pages which + can lead to a performance degradation for some + workloads. Also there will be memory allocation + required when hugetlb pages are freed from the + pool which can lead to corner cases under heavy + memory pressure. + Format: { on | off (default) } + + on: enable the feature + off: disable the feature + hung_task_panic= [KNL] Should the hung task detector generate panics. Format: 0 | 1 --- a/Documentation/admin-guide/mm/hugetlbpage.rst~mm-hugetlb-add-a-kernel-parameter-hugetlb_free_vmemmap +++ a/Documentation/admin-guide/mm/hugetlbpage.rst @@ -153,6 +153,9 @@ default_hugepagesz will all result in 256 2M huge pages being allocated. Valid default huge page size is architecture dependent. +hugetlb_free_vmemmap + When CONFIG_HUGETLB_PAGE_FREE_VMEMMAP is set, this enables freeing + unused vmemmap pages associated with each HugeTLB page. When multiple huge page sizes are supported, ``/proc/sys/vm/nr_hugepages`` indicates the current number of pre-allocated huge pages of the default size. --- a/include/linux/hugetlb.h~mm-hugetlb-add-a-kernel-parameter-hugetlb_free_vmemmap +++ a/include/linux/hugetlb.h @@ -892,6 +892,20 @@ static inline void huge_ptep_modify_prot } #endif +#ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP +extern bool hugetlb_free_vmemmap_enabled; + +static inline bool is_hugetlb_free_vmemmap_enabled(void) +{ + return hugetlb_free_vmemmap_enabled; +} +#else +static inline bool is_hugetlb_free_vmemmap_enabled(void) +{ + return false; +} +#endif + #else /* CONFIG_HUGETLB_PAGE */ struct hstate {}; @@ -1046,6 +1060,11 @@ static inline void set_huge_swap_pte_at( pte_t *ptep, pte_t pte, unsigned long sz) { } + +static inline bool is_hugetlb_free_vmemmap_enabled(void) +{ + return false; +} #endif /* CONFIG_HUGETLB_PAGE */ static inline spinlock_t *huge_pte_lock(struct hstate *h, --- a/mm/hugetlb_vmemmap.c~mm-hugetlb-add-a-kernel-parameter-hugetlb_free_vmemmap +++ a/mm/hugetlb_vmemmap.c @@ -168,6 +168,8 @@ * (last) level. So this type of HugeTLB page can be optimized only when its * size of the struct page structs is greater than 2 pages. */ +#define pr_fmt(fmt) "HugeTLB: " fmt + #include "hugetlb_vmemmap.h" /* @@ -180,6 +182,28 @@ #define RESERVE_VMEMMAP_NR 2U #define RESERVE_VMEMMAP_SIZE (RESERVE_VMEMMAP_NR << PAGE_SHIFT) +bool hugetlb_free_vmemmap_enabled; + +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)))) { + pr_warn("cannot free vmemmap pages because \"struct page\" crosses page boundaries\n"); + return 0; + } + + if (!buf) + return -EINVAL; + + if (!strcmp(buf, "on")) + hugetlb_free_vmemmap_enabled = true; + else if (strcmp(buf, "off")) + return -EINVAL; + + return 0; +} +early_param("hugetlb_free_vmemmap", early_hugetlb_free_vmemmap_param); + static inline unsigned long free_vmemmap_pages_size_per_hpage(struct hstate *h) { return (unsigned long)free_vmemmap_pages_per_hpage(h) << PAGE_SHIFT; _
