linux/mm/hugetlb_vmemmap.c
Yu Zhao c2a967f6ab mm/hugetlb_vmemmap: don't synchronize_rcu() without HVO
hugetlb_vmemmap_optimize_folio() and hugetlb_vmemmap_restore_folio() are
wrappers meant to be called regardless of whether HVO is enabled. 
Therefore, they should not call synchronize_rcu().  Otherwise, it
regresses use cases not enabling HVO.

So move synchronize_rcu() to __hugetlb_vmemmap_optimize_folio() and
__hugetlb_vmemmap_restore_folio(), and call it once for each batch of
folios when HVO is enabled.

Link: https://lkml.kernel.org/r/20240719042503.2752316-1-yuzhao@google.com
Fixes: bd225530a4 ("mm/hugetlb_vmemmap: fix race with speculative PFN walkers")
Signed-off-by: Yu Zhao <yuzhao@google.com>
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202407091001.1250ad4a-oliver.sang@intel.com
Reported-by: Janosch Frank <frankja@linux.ibm.com>
Tested-by: Marc Hartmayer <mhartmay@linux.ibm.com>
Acked-by: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2024-09-01 20:25:45 -07:00

722 lines
22 KiB
C

// SPDX-License-Identifier: GPL-2.0
/*
* HugeTLB Vmemmap Optimization (HVO)
*
* Copyright (c) 2020, ByteDance. All rights reserved.
*
* Author: Muchun Song <songmuchun@bytedance.com>
*
* See Documentation/mm/vmemmap_dedup.rst
*/
#define pr_fmt(fmt) "HugeTLB: " fmt
#include <linux/pgtable.h>
#include <linux/moduleparam.h>
#include <linux/bootmem_info.h>
#include <linux/mmdebug.h>
#include <linux/pagewalk.h>
#include <asm/pgalloc.h>
#include <asm/tlbflush.h>
#include "hugetlb_vmemmap.h"
/**
* struct vmemmap_remap_walk - walk vmemmap page table
*
* @remap_pte: called for each lowest-level entry (PTE).
* @nr_walked: the number of walked pte.
* @reuse_page: the page which is reused for the tail vmemmap pages.
* @reuse_addr: the virtual address of the @reuse_page page.
* @vmemmap_pages: the list head of the vmemmap pages that can be freed
* or is mapped from.
* @flags: used to modify behavior in vmemmap page table walking
* operations.
*/
struct vmemmap_remap_walk {
void (*remap_pte)(pte_t *pte, unsigned long addr,
struct vmemmap_remap_walk *walk);
unsigned long nr_walked;
struct page *reuse_page;
unsigned long reuse_addr;
struct list_head *vmemmap_pages;
/* Skip the TLB flush when we split the PMD */
#define VMEMMAP_SPLIT_NO_TLB_FLUSH BIT(0)
/* Skip the TLB flush when we remap the PTE */
#define VMEMMAP_REMAP_NO_TLB_FLUSH BIT(1)
/* synchronize_rcu() to avoid writes from page_ref_add_unless() */
#define VMEMMAP_SYNCHRONIZE_RCU BIT(2)
unsigned long flags;
};
static int vmemmap_split_pmd(pmd_t *pmd, struct page *head, unsigned long start,
struct vmemmap_remap_walk *walk)
{
pmd_t __pmd;
int i;
unsigned long addr = start;
pte_t *pgtable;
pgtable = pte_alloc_one_kernel(&init_mm);
if (!pgtable)
return -ENOMEM;
pmd_populate_kernel(&init_mm, &__pmd, pgtable);
for (i = 0; i < PTRS_PER_PTE; i++, addr += PAGE_SIZE) {
pte_t entry, *pte;
pgprot_t pgprot = PAGE_KERNEL;
entry = mk_pte(head + i, pgprot);
pte = pte_offset_kernel(&__pmd, addr);
set_pte_at(&init_mm, addr, pte, entry);
}
spin_lock(&init_mm.page_table_lock);
if (likely(pmd_leaf(*pmd))) {
/*
* Higher order allocations from buddy allocator must be able to
* be treated as indepdenent small pages (as they can be freed
* individually).
*/
if (!PageReserved(head))
split_page(head, get_order(PMD_SIZE));
/* Make pte visible before pmd. See comment in pmd_install(). */
smp_wmb();
pmd_populate_kernel(&init_mm, pmd, pgtable);
if (!(walk->flags & VMEMMAP_SPLIT_NO_TLB_FLUSH))
flush_tlb_kernel_range(start, start + PMD_SIZE);
} else {
pte_free_kernel(&init_mm, pgtable);
}
spin_unlock(&init_mm.page_table_lock);
return 0;
}
static int vmemmap_pmd_entry(pmd_t *pmd, unsigned long addr,
unsigned long next, struct mm_walk *walk)
{
int ret = 0;
struct page *head;
struct vmemmap_remap_walk *vmemmap_walk = walk->private;
/* Only splitting, not remapping the vmemmap pages. */
if (!vmemmap_walk->remap_pte)
walk->action = ACTION_CONTINUE;
spin_lock(&init_mm.page_table_lock);
head = pmd_leaf(*pmd) ? pmd_page(*pmd) : NULL;
/*
* Due to HugeTLB alignment requirements and the vmemmap
* pages being at the start of the hotplugged memory
* region in memory_hotplug.memmap_on_memory case. Checking
* the vmemmap page associated with the first vmemmap page
* if it is self-hosted is sufficient.
*
* [ hotplugged memory ]
* [ section ][...][ section ]
* [ vmemmap ][ usable memory ]
* ^ | ^ |
* +--+ | |
* +------------------------+
*/
if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG) && unlikely(!vmemmap_walk->nr_walked)) {
struct page *page = head ? head + pte_index(addr) :
pte_page(ptep_get(pte_offset_kernel(pmd, addr)));
if (PageVmemmapSelfHosted(page))
ret = -ENOTSUPP;
}
spin_unlock(&init_mm.page_table_lock);
if (!head || ret)
return ret;
return vmemmap_split_pmd(pmd, head, addr & PMD_MASK, vmemmap_walk);
}
static int vmemmap_pte_entry(pte_t *pte, unsigned long addr,
unsigned long next, struct mm_walk *walk)
{
struct vmemmap_remap_walk *vmemmap_walk = walk->private;
/*
* The reuse_page is found 'first' in page table walking before
* starting remapping.
*/
if (!vmemmap_walk->reuse_page)
vmemmap_walk->reuse_page = pte_page(ptep_get(pte));
else
vmemmap_walk->remap_pte(pte, addr, vmemmap_walk);
vmemmap_walk->nr_walked++;
return 0;
}
static const struct mm_walk_ops vmemmap_remap_ops = {
.pmd_entry = vmemmap_pmd_entry,
.pte_entry = vmemmap_pte_entry,
};
static int vmemmap_remap_range(unsigned long start, unsigned long end,
struct vmemmap_remap_walk *walk)
{
int ret;
VM_BUG_ON(!PAGE_ALIGNED(start | end));
mmap_read_lock(&init_mm);
ret = walk_page_range_novma(&init_mm, start, end, &vmemmap_remap_ops,
NULL, walk);
mmap_read_unlock(&init_mm);
if (ret)
return ret;
if (walk->remap_pte && !(walk->flags & VMEMMAP_REMAP_NO_TLB_FLUSH))
flush_tlb_kernel_range(start, end);
return 0;
}
/*
* Free a vmemmap page. A vmemmap page can be allocated from the memblock
* allocator or buddy allocator. If the PG_reserved flag is set, it means
* that it allocated from the memblock allocator, just free it via the
* free_bootmem_page(). Otherwise, use __free_page().
*/
static inline void free_vmemmap_page(struct page *page)
{
if (PageReserved(page)) {
memmap_boot_pages_add(-1);
free_bootmem_page(page);
} else {
memmap_pages_add(-1);
__free_page(page);
}
}
/* Free a list of the vmemmap pages */
static void free_vmemmap_page_list(struct list_head *list)
{
struct page *page, *next;
list_for_each_entry_safe(page, next, list, lru)
free_vmemmap_page(page);
}
static void vmemmap_remap_pte(pte_t *pte, unsigned long addr,
struct vmemmap_remap_walk *walk)
{
/*
* Remap the tail pages as read-only to catch illegal write operation
* to the tail pages.
*/
pgprot_t pgprot = PAGE_KERNEL_RO;
struct page *page = pte_page(ptep_get(pte));
pte_t entry;
/* Remapping the head page requires r/w */
if (unlikely(addr == walk->reuse_addr)) {
pgprot = PAGE_KERNEL;
list_del(&walk->reuse_page->lru);
/*
* Makes sure that preceding stores to the page contents from
* vmemmap_remap_free() become visible before the set_pte_at()
* write.
*/
smp_wmb();
}
entry = mk_pte(walk->reuse_page, pgprot);
list_add(&page->lru, walk->vmemmap_pages);
set_pte_at(&init_mm, addr, pte, entry);
}
/*
* How many struct page structs need to be reset. When we reuse the head
* struct page, the special metadata (e.g. page->flags or page->mapping)
* cannot copy to the tail struct page structs. The invalid value will be
* checked in the free_tail_page_prepare(). In order to avoid the message
* of "corrupted mapping in tail page". We need to reset at least 3 (one
* head struct page struct and two tail struct page structs) struct page
* structs.
*/
#define NR_RESET_STRUCT_PAGE 3
static inline void reset_struct_pages(struct page *start)
{
struct page *from = start + NR_RESET_STRUCT_PAGE;
BUILD_BUG_ON(NR_RESET_STRUCT_PAGE * 2 > PAGE_SIZE / sizeof(struct page));
memcpy(start, from, sizeof(*from) * NR_RESET_STRUCT_PAGE);
}
static void vmemmap_restore_pte(pte_t *pte, unsigned long addr,
struct vmemmap_remap_walk *walk)
{
pgprot_t pgprot = PAGE_KERNEL;
struct page *page;
void *to;
BUG_ON(pte_page(ptep_get(pte)) != walk->reuse_page);
page = list_first_entry(walk->vmemmap_pages, struct page, lru);
list_del(&page->lru);
to = page_to_virt(page);
copy_page(to, (void *)walk->reuse_addr);
reset_struct_pages(to);
/*
* Makes sure that preceding stores to the page contents become visible
* before the set_pte_at() write.
*/
smp_wmb();
set_pte_at(&init_mm, addr, pte, mk_pte(page, pgprot));
}
/**
* vmemmap_remap_split - split the vmemmap virtual address range [@start, @end)
* backing PMDs of the directmap into PTEs
* @start: start address of the vmemmap virtual address range that we want
* to remap.
* @end: end address of the vmemmap virtual address range that we want to
* remap.
* @reuse: reuse address.
*
* Return: %0 on success, negative error code otherwise.
*/
static int vmemmap_remap_split(unsigned long start, unsigned long end,
unsigned long reuse)
{
struct vmemmap_remap_walk walk = {
.remap_pte = NULL,
.flags = VMEMMAP_SPLIT_NO_TLB_FLUSH,
};
/* See the comment in the vmemmap_remap_free(). */
BUG_ON(start - reuse != PAGE_SIZE);
return vmemmap_remap_range(reuse, end, &walk);
}
/**
* vmemmap_remap_free - remap the vmemmap virtual address range [@start, @end)
* to the page which @reuse is mapped to, then free vmemmap
* which the range are mapped to.
* @start: start address of the vmemmap virtual address range that we want
* to remap.
* @end: end address of the vmemmap virtual address range that we want to
* remap.
* @reuse: reuse address.
* @vmemmap_pages: list to deposit vmemmap pages to be freed. It is callers
* responsibility to free pages.
* @flags: modifications to vmemmap_remap_walk flags
*
* Return: %0 on success, negative error code otherwise.
*/
static int vmemmap_remap_free(unsigned long start, unsigned long end,
unsigned long reuse,
struct list_head *vmemmap_pages,
unsigned long flags)
{
int ret;
struct vmemmap_remap_walk walk = {
.remap_pte = vmemmap_remap_pte,
.reuse_addr = reuse,
.vmemmap_pages = vmemmap_pages,
.flags = flags,
};
int nid = page_to_nid((struct page *)reuse);
gfp_t gfp_mask = GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN;
/*
* Allocate a new head vmemmap page to avoid breaking a contiguous
* block of struct page memory when freeing it back to page allocator
* in free_vmemmap_page_list(). This will allow the likely contiguous
* struct page backing memory to be kept contiguous and allowing for
* more allocations of hugepages. Fallback to the currently
* mapped head page in case should it fail to allocate.
*/
walk.reuse_page = alloc_pages_node(nid, gfp_mask, 0);
if (walk.reuse_page) {
copy_page(page_to_virt(walk.reuse_page),
(void *)walk.reuse_addr);
list_add(&walk.reuse_page->lru, vmemmap_pages);
memmap_pages_add(1);
}
/*
* In order to make remapping routine most efficient for the huge pages,
* the routine of vmemmap page table walking has the following rules
* (see more details from the vmemmap_pte_range()):
*
* - The range [@start, @end) and the range [@reuse, @reuse + PAGE_SIZE)
* should be continuous.
* - The @reuse address is part of the range [@reuse, @end) that we are
* walking which is passed to vmemmap_remap_range().
* - The @reuse address is the first in the complete range.
*
* So we need to make sure that @start and @reuse meet the above rules.
*/
BUG_ON(start - reuse != PAGE_SIZE);
ret = vmemmap_remap_range(reuse, end, &walk);
if (ret && walk.nr_walked) {
end = reuse + walk.nr_walked * PAGE_SIZE;
/*
* vmemmap_pages contains pages from the previous
* vmemmap_remap_range call which failed. These
* are pages which were removed from the vmemmap.
* They will be restored in the following call.
*/
walk = (struct vmemmap_remap_walk) {
.remap_pte = vmemmap_restore_pte,
.reuse_addr = reuse,
.vmemmap_pages = vmemmap_pages,
.flags = 0,
};
vmemmap_remap_range(reuse, end, &walk);
}
return ret;
}
static int alloc_vmemmap_page_list(unsigned long start, unsigned long end,
struct list_head *list)
{
gfp_t gfp_mask = GFP_KERNEL | __GFP_RETRY_MAYFAIL;
unsigned long nr_pages = (end - start) >> PAGE_SHIFT;
int nid = page_to_nid((struct page *)start);
struct page *page, *next;
int i;
for (i = 0; i < nr_pages; i++) {
page = alloc_pages_node(nid, gfp_mask, 0);
if (!page)
goto out;
list_add(&page->lru, list);
}
memmap_pages_add(nr_pages);
return 0;
out:
list_for_each_entry_safe(page, next, list, lru)
__free_page(page);
return -ENOMEM;
}
/**
* vmemmap_remap_alloc - remap the vmemmap virtual address range [@start, end)
* to the page which is from the @vmemmap_pages
* respectively.
* @start: start address of the vmemmap virtual address range that we want
* to remap.
* @end: end address of the vmemmap virtual address range that we want to
* remap.
* @reuse: reuse address.
* @flags: modifications to vmemmap_remap_walk flags
*
* Return: %0 on success, negative error code otherwise.
*/
static int vmemmap_remap_alloc(unsigned long start, unsigned long end,
unsigned long reuse, unsigned long flags)
{
LIST_HEAD(vmemmap_pages);
struct vmemmap_remap_walk walk = {
.remap_pte = vmemmap_restore_pte,
.reuse_addr = reuse,
.vmemmap_pages = &vmemmap_pages,
.flags = flags,
};
/* See the comment in the vmemmap_remap_free(). */
BUG_ON(start - reuse != PAGE_SIZE);
if (alloc_vmemmap_page_list(start, end, &vmemmap_pages))
return -ENOMEM;
return vmemmap_remap_range(reuse, end, &walk);
}
DEFINE_STATIC_KEY_FALSE(hugetlb_optimize_vmemmap_key);
EXPORT_SYMBOL(hugetlb_optimize_vmemmap_key);
static bool vmemmap_optimize_enabled = IS_ENABLED(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON);
core_param(hugetlb_free_vmemmap, vmemmap_optimize_enabled, bool, 0);
static int __hugetlb_vmemmap_restore_folio(const struct hstate *h,
struct folio *folio, unsigned long flags)
{
int ret;
unsigned long vmemmap_start = (unsigned long)&folio->page, vmemmap_end;
unsigned long vmemmap_reuse;
VM_WARN_ON_ONCE_FOLIO(!folio_test_hugetlb(folio), folio);
VM_WARN_ON_ONCE_FOLIO(folio_ref_count(folio), folio);
if (!folio_test_hugetlb_vmemmap_optimized(folio))
return 0;
if (flags & VMEMMAP_SYNCHRONIZE_RCU)
synchronize_rcu();
vmemmap_end = vmemmap_start + hugetlb_vmemmap_size(h);
vmemmap_reuse = vmemmap_start;
vmemmap_start += HUGETLB_VMEMMAP_RESERVE_SIZE;
/*
* The pages which the vmemmap virtual address range [@vmemmap_start,
* @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_start, vmemmap_end, vmemmap_reuse, flags);
if (!ret) {
folio_clear_hugetlb_vmemmap_optimized(folio);
static_branch_dec(&hugetlb_optimize_vmemmap_key);
}
return ret;
}
/**
* hugetlb_vmemmap_restore_folio - restore previously optimized (by
* hugetlb_vmemmap_optimize_folio()) vmemmap pages which
* will be reallocated and remapped.
* @h: struct hstate.
* @folio: the folio whose vmemmap pages will be restored.
*
* Return: %0 if @folio's vmemmap pages have been reallocated and remapped,
* negative error code otherwise.
*/
int hugetlb_vmemmap_restore_folio(const struct hstate *h, struct folio *folio)
{
return __hugetlb_vmemmap_restore_folio(h, folio, VMEMMAP_SYNCHRONIZE_RCU);
}
/**
* hugetlb_vmemmap_restore_folios - restore vmemmap for every folio on the list.
* @h: hstate.
* @folio_list: list of folios.
* @non_hvo_folios: Output list of folios for which vmemmap exists.
*
* Return: number of folios for which vmemmap was restored, or an error code
* if an error was encountered restoring vmemmap for a folio.
* Folios that have vmemmap are moved to the non_hvo_folios
* list. Processing of entries stops when the first error is
* encountered. The folio that experienced the error and all
* non-processed folios will remain on folio_list.
*/
long hugetlb_vmemmap_restore_folios(const struct hstate *h,
struct list_head *folio_list,
struct list_head *non_hvo_folios)
{
struct folio *folio, *t_folio;
long restored = 0;
long ret = 0;
unsigned long flags = VMEMMAP_REMAP_NO_TLB_FLUSH | VMEMMAP_SYNCHRONIZE_RCU;
list_for_each_entry_safe(folio, t_folio, folio_list, lru) {
if (folio_test_hugetlb_vmemmap_optimized(folio)) {
ret = __hugetlb_vmemmap_restore_folio(h, folio, flags);
/* only need to synchronize_rcu() once for each batch */
flags &= ~VMEMMAP_SYNCHRONIZE_RCU;
if (ret)
break;
restored++;
}
/* Add non-optimized folios to output list */
list_move(&folio->lru, non_hvo_folios);
}
if (restored)
flush_tlb_all();
if (!ret)
ret = restored;
return ret;
}
/* Return true iff a HugeTLB whose vmemmap should and can be optimized. */
static bool vmemmap_should_optimize_folio(const struct hstate *h, struct folio *folio)
{
if (folio_test_hugetlb_vmemmap_optimized(folio))
return false;
if (!READ_ONCE(vmemmap_optimize_enabled))
return false;
if (!hugetlb_vmemmap_optimizable(h))
return false;
return true;
}
static int __hugetlb_vmemmap_optimize_folio(const struct hstate *h,
struct folio *folio,
struct list_head *vmemmap_pages,
unsigned long flags)
{
int ret = 0;
unsigned long vmemmap_start = (unsigned long)&folio->page, vmemmap_end;
unsigned long vmemmap_reuse;
VM_WARN_ON_ONCE_FOLIO(!folio_test_hugetlb(folio), folio);
VM_WARN_ON_ONCE_FOLIO(folio_ref_count(folio), folio);
if (!vmemmap_should_optimize_folio(h, folio))
return ret;
static_branch_inc(&hugetlb_optimize_vmemmap_key);
if (flags & VMEMMAP_SYNCHRONIZE_RCU)
synchronize_rcu();
/*
* Very Subtle
* If VMEMMAP_REMAP_NO_TLB_FLUSH is set, TLB flushing is not performed
* immediately after remapping. As a result, subsequent accesses
* and modifications to struct pages associated with the hugetlb
* page could be to the OLD struct pages. Set the vmemmap optimized
* flag here so that it is copied to the new head page. This keeps
* the old and new struct pages in sync.
* If there is an error during optimization, we will immediately FLUSH
* the TLB and clear the flag below.
*/
folio_set_hugetlb_vmemmap_optimized(folio);
vmemmap_end = vmemmap_start + hugetlb_vmemmap_size(h);
vmemmap_reuse = vmemmap_start;
vmemmap_start += HUGETLB_VMEMMAP_RESERVE_SIZE;
/*
* Remap the vmemmap virtual address range [@vmemmap_start, @vmemmap_end)
* to the page which @vmemmap_reuse is mapped to. Add pages previously
* mapping the range to vmemmap_pages list so that they can be freed by
* the caller.
*/
ret = vmemmap_remap_free(vmemmap_start, vmemmap_end, vmemmap_reuse,
vmemmap_pages, flags);
if (ret) {
static_branch_dec(&hugetlb_optimize_vmemmap_key);
folio_clear_hugetlb_vmemmap_optimized(folio);
}
return ret;
}
/**
* hugetlb_vmemmap_optimize_folio - optimize @folio's vmemmap pages.
* @h: struct hstate.
* @folio: the folio whose vmemmap pages will be optimized.
*
* This function only tries to optimize @folio's vmemmap pages and does not
* guarantee that the optimization will succeed after it returns. The caller
* can use folio_test_hugetlb_vmemmap_optimized(@folio) to detect if @folio's
* vmemmap pages have been optimized.
*/
void hugetlb_vmemmap_optimize_folio(const struct hstate *h, struct folio *folio)
{
LIST_HEAD(vmemmap_pages);
__hugetlb_vmemmap_optimize_folio(h, folio, &vmemmap_pages, VMEMMAP_SYNCHRONIZE_RCU);
free_vmemmap_page_list(&vmemmap_pages);
}
static int hugetlb_vmemmap_split_folio(const struct hstate *h, struct folio *folio)
{
unsigned long vmemmap_start = (unsigned long)&folio->page, vmemmap_end;
unsigned long vmemmap_reuse;
if (!vmemmap_should_optimize_folio(h, folio))
return 0;
vmemmap_end = vmemmap_start + hugetlb_vmemmap_size(h);
vmemmap_reuse = vmemmap_start;
vmemmap_start += HUGETLB_VMEMMAP_RESERVE_SIZE;
/*
* Split PMDs on the vmemmap virtual address range [@vmemmap_start,
* @vmemmap_end]
*/
return vmemmap_remap_split(vmemmap_start, vmemmap_end, vmemmap_reuse);
}
void hugetlb_vmemmap_optimize_folios(struct hstate *h, struct list_head *folio_list)
{
struct folio *folio;
LIST_HEAD(vmemmap_pages);
unsigned long flags = VMEMMAP_REMAP_NO_TLB_FLUSH | VMEMMAP_SYNCHRONIZE_RCU;
list_for_each_entry(folio, folio_list, lru) {
int ret = hugetlb_vmemmap_split_folio(h, folio);
/*
* Spliting the PMD requires allocating a page, thus lets fail
* early once we encounter the first OOM. No point in retrying
* as it can be dynamically done on remap with the memory
* we get back from the vmemmap deduplication.
*/
if (ret == -ENOMEM)
break;
}
flush_tlb_all();
list_for_each_entry(folio, folio_list, lru) {
int ret;
ret = __hugetlb_vmemmap_optimize_folio(h, folio, &vmemmap_pages, flags);
/* only need to synchronize_rcu() once for each batch */
flags &= ~VMEMMAP_SYNCHRONIZE_RCU;
/*
* Pages to be freed may have been accumulated. If we
* encounter an ENOMEM, free what we have and try again.
* This can occur in the case that both spliting fails
* halfway and head page allocation also failed. In this
* case __hugetlb_vmemmap_optimize_folio() would free memory
* allowing more vmemmap remaps to occur.
*/
if (ret == -ENOMEM && !list_empty(&vmemmap_pages)) {
flush_tlb_all();
free_vmemmap_page_list(&vmemmap_pages);
INIT_LIST_HEAD(&vmemmap_pages);
__hugetlb_vmemmap_optimize_folio(h, folio, &vmemmap_pages, flags);
}
}
flush_tlb_all();
free_vmemmap_page_list(&vmemmap_pages);
}
static struct ctl_table hugetlb_vmemmap_sysctls[] = {
{
.procname = "hugetlb_optimize_vmemmap",
.data = &vmemmap_optimize_enabled,
.maxlen = sizeof(vmemmap_optimize_enabled),
.mode = 0644,
.proc_handler = proc_dobool,
},
};
static int __init hugetlb_vmemmap_init(void)
{
const struct hstate *h;
/* HUGETLB_VMEMMAP_RESERVE_SIZE should cover all used struct pages */
BUILD_BUG_ON(__NR_USED_SUBPAGE > HUGETLB_VMEMMAP_RESERVE_PAGES);
for_each_hstate(h) {
if (hugetlb_vmemmap_optimizable(h)) {
register_sysctl_init("vm", hugetlb_vmemmap_sysctls);
break;
}
}
return 0;
}
late_initcall(hugetlb_vmemmap_init);