// SPDX-License-Identifier: GPL-2.0
/*
* Optimize vmemmap pages associated with HugeTLB
*
* Copyright (c) 2020, Bytedance. All rights reserved.
*
* Author: Muchun Song <songmuchun@bytedance.com>
*
* See Documentation/vm/vmemmap_dedup.rst
*/
#define pr_fmt(fmt) "HugeTLB: " fmt
#include <linux/memory_hotplug.h>
#include "hugetlb_vmemmap.h"
/*
* There are a lot of struct page structures associated with each HugeTLB page.
* For tail pages, the value of compound_head is the same. So we can reuse first
* page of head page structures. We map the virtual addresses of all the pages
* of tail page structures to the head page struct, and then free these page
* frames. Therefore, we need to reserve one pages as vmemmap areas.
*/
#define RESERVE_VMEMMAP_NR 1U
#define RESERVE_VMEMMAP_SIZE (RESERVE_VMEMMAP_NR << PAGE_SHIFT)
enum vmemmap_optimize_mode {
VMEMMAP_OPTIMIZE_OFF,
VMEMMAP_OPTIMIZE_ON,
};
DEFINE_STATIC_KEY_MAYBE(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON,
hugetlb_optimize_vmemmap_key);
EXPORT_SYMBOL(hugetlb_optimize_vmemmap_key);
static enum vmemmap_optimize_mode vmemmap_optimize_mode =
IS_ENABLED(CONFIG_HUGETLB_PAGE_FREE_VMEMMAP_DEFAULT_ON);
static void vmemmap_optimize_mode_switch(enum vmemmap_optimize_mode to)
{
if (vmemmap_optimize_mode == to)
return;
if (to == VMEMMAP_OPTIMIZE_OFF)
static_branch_dec(&hugetlb_optimize_vmemmap_key);
else
static_branch_inc(&hugetlb_optimize_vmemmap_key);
WRITE_ONCE(vmemmap_optimize_mode, to);
}
static int __init hugetlb_vmemmap_early_param(char *buf)
{
bool enable;
enum vmemmap_optimize_mode mode;
if (kstrtobool(buf, &enable))
return -EINVAL;
mode = enable ? VMEMMAP_OPTIMIZE_ON : VMEMMAP_OPTIMIZE_OFF;
vmemmap_optimize_mode_switch(mode);
return 0;
}
early_param("hugetlb_free_vmemmap", hugetlb_vmemmap_early_param);
/*
* Previously discarded vmemmap pages will be allocated and remapping
* after this function returns zero.
*/
int hugetlb_vmemmap_alloc(struct hstate *h, struct page *head)
{
int ret;
unsigned long vmemmap_addr = (unsigned long)head;
unsigned long vmemmap_end, vmemmap_reuse, vmemmap_pages;
if (!HPageVmemmapOptimized(head))
return 0;
vmemmap_addr += RESERVE_VMEMMAP_SIZE;
vmemmap_pages = hugetlb_optimize_vmemmap_pages(h);
vmemmap_end = vmemmap_addr + (vmemmap_pages << PAGE_SHIFT);
vmemmap_reuse = vmemmap_addr - PAGE_SIZE;
/*
* The pages which the vmemmap virtual address range [@vmemmap_addr,
* @vmemmap_end) are mapped to are freed to the buddy allocator, and
* the range is mapped to the page which @vmemmap_reuse is mapped to.
* When a HugeTLB page is freed to the buddy allocator, previously
* discarded vmemmap pages must be allocated and remapping.
*/
ret = vmemmap_remap_alloc(vmemmap_addr, vmemmap_end, vmemmap_reuse,
GFP_KERNEL | __GFP_NORETRY | __GFP_THISNODE);
if (!ret) {
ClearHPageVmemmapOptimized(head);
static_branch_dec(&hugetlb_optimize_vmemmap_key);
}
return ret;
}
void hugetlb_vmemmap_free(struct hstate *h, struct page *head)
{
unsigned long vmemmap_addr = (unsigned long)head;
unsigned long vmemmap_end, vmemmap_reuse, vmemmap_pages;
vmemmap_pages = hugetlb_optimize_vmemmap_pages(h);
if (!vmemmap_pages)
return;
if (READ_ONCE(vmemmap_optimize_mode) == VMEMMAP_OPTIMIZE_OFF)
return;
static_branch_inc(&hugetlb_optimize_vmemmap_key);
vmemmap_addr += RESERVE_VMEMMAP_SIZE;
vmemmap_end = vmemmap_addr + (vmemmap_pages << PAGE_SHIFT);
vmemmap_reuse = vmemmap_addr - PAGE_SIZE;
/*
* Remap the vmemmap virtual address range [@vmemmap_addr, @vmemmap_end)
* to the page which @vmemmap_reuse is mapped to, then free the pages
* which the range [@vmemmap_addr, @vmemmap_end] is mapped to.
*/
if (vmemmap_remap_free(vmemmap_addr, vmemmap_end, vmemmap_reuse))
static_branch_dec(&hugetlb_optimize_vmemmap_key);
else
SetHPageVmemmapOptimized(head);
}
void __init hugetlb_vmemmap_init(struct hstate *h)
{
unsigned int nr_pages = pages_per_huge_page(h);
unsigned int vmemmap_pages;
/*
* There are only (RESERVE_VMEMMAP_SIZE / sizeof(struct page)) struct
* page structs that can be used when CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP,
* so add a BUILD_BUG_ON to catch invalid usage of the tail struct page.
*/
BUILD_BUG_ON(__NR_USED_SUBPAGE >=
RESERVE_VMEMMAP_SIZE / sizeof(struct page));
if (!is_power_of_2(sizeof(struct page))) {
pr_warn_once("cannot optimize vmemmap pages because \"struct page\" crosses page boundaries\n");
static_branch_disable(&hugetlb_optimize_vmemmap_key);
return;
}
vmemmap_pages = (nr_pages * sizeof(struct page)) >> PAGE_SHIFT;
/*
* The head page is not to be freed to buddy allocator, the other tail
* pages will map to the head page, so they can be freed.
*
* Could RESERVE_VMEMMAP_NR be greater than @vmemmap_pages? It is true
* on some architectures (e.g. aarch64). See Documentation/arm64/
* hugetlbpage.rst for more details.
*/
if (likely(vmemmap_pages > RESERVE_VMEMMAP_NR))
h->optimize_vmemmap_pages = vmemmap_pages - RESERVE_VMEMMAP_NR;
pr_info("can optimize %d vmemmap pages for %s\n",
h->optimize_vmemmap_pages, h->name);
}
#ifdef CONFIG_PROC_SYSCTL
static int hugetlb_optimize_vmemmap_handler(struct ctl_table *table, int write,
void *buffer, size_t *length,
loff_t *ppos)
{
int ret;
enum vmemmap_optimize_mode mode;
static DEFINE_MUTEX(sysctl_mutex);
if (write && !capable(CAP_SYS_ADMIN))
return -EPERM;
mutex_lock(&sysctl_mutex);
mode = vmemmap_optimize_mode;
table->data = &mode;
ret = proc_dointvec_minmax(table, write, buffer, length, ppos);
if (write && !ret)
vmemmap_optimize_mode_switch(mode);
mutex_unlock(&sysctl_mutex);
return ret;
}
static struct ctl_table hugetlb_vmemmap_sysctls[] = {
{
.procname = "hugetlb_optimize_vmemmap",
.maxlen = sizeof(enum vmemmap_optimize_mode),
.mode = 0644,
.proc_handler = hugetlb_optimize_vmemmap_handler,
.extra1 = SYSCTL_ZERO,
.extra2 = SYSCTL_ONE,
},
{ }
};
static __init int hugetlb_vmemmap_sysctls_init(void)
{
/*
* If "memory_hotplug.memmap_on_memory" is enabled or "struct page"
* crosses page boundaries, the vmemmap pages cannot be optimized.
*/
if (!mhp_memmap_on_memory() && is_power_of_2(sizeof(struct page)))
register_sysctl_init("vm", hugetlb_vmemmap_sysctls);
return 0;
}
late_initcall(hugetlb_vmemmap_sysctls_init);
#endif /* CONFIG_PROC_SYSCTL */
