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@bytedance.com
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: Barry Song <song.bao.hua@hisilicon.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Tested-by: Chen Huang <chenhuang5@huawei.com>
Tested-by: Bodeddula Balasubramaniam <bodeddub@amazon.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: HORIGUCHI NAOYA <naoya.horiguchi@nec.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Joao Martins <joao.m.martins@oracle.com>
Cc: Joerg Roedel <jroedel@suse.de>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mina Almasry <almasrymina@google.com>
Cc: Oliver Neukum <oneukum@suse.com>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Xiongchun Duan <duanxiongchun@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 566c4b9..b787a99 100644 (file)
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/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

diff --git a/Documentation/admin-guide/mm/hugetlbpage.rst b/Documentation/admin-guide/mm/hugetlbpage.rst
index 6988895..8abaeb1 100644 (file)
--- a/Documentation/admin-guide/mm/hugetlbpage.rst
+++ b/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.

diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 65ea585..9d9d18d 100644 (file)
--- a/arch/x86/mm/init_64.c
+++ b/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 long start, unsigned long end, int node,
        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(unsigned long section_nr,
        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(unsigned long section_nr,
                }
                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))

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 3578d9d..9ad9984 100644 (file)
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -892,6 +892,20 @@ static inline void huge_ptep_modify_prot_commit(struct vm_area_struct *vma,
 }
 #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(struct mm_struct *mm, unsigned long addr
                                        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,

diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index a897c77..3070e14 100644 (file)
--- a/mm/hugetlb_vmemmap.c
+++ b/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;