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![Mel Gorman](/assets/img/avatar_default.png)
When overcommit is disabled, the core VM accounts for pages used by anonymous
shared, private mappings and special mappings. It keeps track of VMAs that
should be accounted for with VM_ACCOUNT and VMAs that never had a reserve
with VM_NORESERVE.
Overcommit for hugetlbfs is much riskier than overcommit for base pages
due to contiguity requirements. It avoids overcommiting on both shared and
private mappings using reservation counters that are checked and updated
during mmap(). This ensures (within limits) that hugepages exist in the
future when faults occurs or it is too easy to applications to be SIGKILLed.
As hugetlbfs makes its own reservations of a different unit to the base page
size, VM_ACCOUNT should never be set. Even if the units were correct, we would
double account for the usage in the core VM and hugetlbfs. VM_NORESERVE may
be set because an application can request no reserves be made for hugetlbfs
at the risk of getting killed later.
With commit fc8744adc8
, VM_NORESERVE and
VM_ACCOUNT are getting unconditionally set for hugetlbfs-backed mappings. This
breaks the accounting for both the core VM and hugetlbfs, can trigger an
OOM storm when hugepage pools are too small lockups and corrupted counters
otherwise are used. This patch brings hugetlbfs more in line with how the
core VM treats VM_NORESERVE but prevents VM_ACCOUNT being set.
Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
260 lines
6.7 KiB
C
260 lines
6.7 KiB
C
/*
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* linux/mm/fremap.c
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*
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* Explicit pagetable population and nonlinear (random) mappings support.
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*
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* started by Ingo Molnar, Copyright (C) 2002, 2003
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*/
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#include <linux/backing-dev.h>
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#include <linux/mm.h>
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#include <linux/swap.h>
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#include <linux/file.h>
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#include <linux/mman.h>
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#include <linux/pagemap.h>
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#include <linux/swapops.h>
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#include <linux/rmap.h>
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#include <linux/module.h>
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#include <linux/syscalls.h>
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#include <linux/mmu_notifier.h>
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#include <asm/mmu_context.h>
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#include <asm/cacheflush.h>
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#include <asm/tlbflush.h>
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#include "internal.h"
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static void zap_pte(struct mm_struct *mm, struct vm_area_struct *vma,
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unsigned long addr, pte_t *ptep)
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{
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pte_t pte = *ptep;
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if (pte_present(pte)) {
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struct page *page;
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flush_cache_page(vma, addr, pte_pfn(pte));
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pte = ptep_clear_flush(vma, addr, ptep);
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page = vm_normal_page(vma, addr, pte);
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if (page) {
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if (pte_dirty(pte))
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set_page_dirty(page);
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page_remove_rmap(page);
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page_cache_release(page);
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update_hiwater_rss(mm);
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dec_mm_counter(mm, file_rss);
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}
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} else {
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if (!pte_file(pte))
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free_swap_and_cache(pte_to_swp_entry(pte));
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pte_clear_not_present_full(mm, addr, ptep, 0);
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}
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}
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/*
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* Install a file pte to a given virtual memory address, release any
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* previously existing mapping.
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*/
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static int install_file_pte(struct mm_struct *mm, struct vm_area_struct *vma,
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unsigned long addr, unsigned long pgoff, pgprot_t prot)
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{
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int err = -ENOMEM;
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pte_t *pte;
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spinlock_t *ptl;
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pte = get_locked_pte(mm, addr, &ptl);
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if (!pte)
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goto out;
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if (!pte_none(*pte))
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zap_pte(mm, vma, addr, pte);
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set_pte_at(mm, addr, pte, pgoff_to_pte(pgoff));
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/*
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* We don't need to run update_mmu_cache() here because the "file pte"
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* being installed by install_file_pte() is not a real pte - it's a
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* non-present entry (like a swap entry), noting what file offset should
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* be mapped there when there's a fault (in a non-linear vma where
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* that's not obvious).
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*/
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pte_unmap_unlock(pte, ptl);
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err = 0;
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out:
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return err;
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}
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static int populate_range(struct mm_struct *mm, struct vm_area_struct *vma,
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unsigned long addr, unsigned long size, pgoff_t pgoff)
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{
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int err;
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do {
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err = install_file_pte(mm, vma, addr, pgoff, vma->vm_page_prot);
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if (err)
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return err;
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size -= PAGE_SIZE;
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addr += PAGE_SIZE;
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pgoff++;
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} while (size);
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return 0;
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}
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/**
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* sys_remap_file_pages - remap arbitrary pages of an existing VM_SHARED vma
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* @start: start of the remapped virtual memory range
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* @size: size of the remapped virtual memory range
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* @prot: new protection bits of the range (see NOTE)
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* @pgoff: to-be-mapped page of the backing store file
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* @flags: 0 or MAP_NONBLOCKED - the later will cause no IO.
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*
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* sys_remap_file_pages remaps arbitrary pages of an existing VM_SHARED vma
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* (shared backing store file).
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*
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* This syscall works purely via pagetables, so it's the most efficient
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* way to map the same (large) file into a given virtual window. Unlike
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* mmap()/mremap() it does not create any new vmas. The new mappings are
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* also safe across swapout.
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*
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* NOTE: the @prot parameter right now is ignored (but must be zero),
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* and the vma's default protection is used. Arbitrary protections
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* might be implemented in the future.
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*/
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SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
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unsigned long, prot, unsigned long, pgoff, unsigned long, flags)
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{
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struct mm_struct *mm = current->mm;
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struct address_space *mapping;
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unsigned long end = start + size;
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struct vm_area_struct *vma;
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int err = -EINVAL;
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int has_write_lock = 0;
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if (prot)
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return err;
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/*
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* Sanitize the syscall parameters:
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*/
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start = start & PAGE_MASK;
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size = size & PAGE_MASK;
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/* Does the address range wrap, or is the span zero-sized? */
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if (start + size <= start)
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return err;
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/* Can we represent this offset inside this architecture's pte's? */
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#if PTE_FILE_MAX_BITS < BITS_PER_LONG
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if (pgoff + (size >> PAGE_SHIFT) >= (1UL << PTE_FILE_MAX_BITS))
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return err;
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#endif
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/* We need down_write() to change vma->vm_flags. */
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down_read(&mm->mmap_sem);
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retry:
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vma = find_vma(mm, start);
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/*
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* Make sure the vma is shared, that it supports prefaulting,
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* and that the remapped range is valid and fully within
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* the single existing vma. vm_private_data is used as a
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* swapout cursor in a VM_NONLINEAR vma.
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*/
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if (!vma || !(vma->vm_flags & VM_SHARED))
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goto out;
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if (vma->vm_private_data && !(vma->vm_flags & VM_NONLINEAR))
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goto out;
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if (!(vma->vm_flags & VM_CAN_NONLINEAR))
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goto out;
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if (end <= start || start < vma->vm_start || end > vma->vm_end)
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goto out;
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/* Must set VM_NONLINEAR before any pages are populated. */
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if (!(vma->vm_flags & VM_NONLINEAR)) {
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/* Don't need a nonlinear mapping, exit success */
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if (pgoff == linear_page_index(vma, start)) {
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err = 0;
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goto out;
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}
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if (!has_write_lock) {
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up_read(&mm->mmap_sem);
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down_write(&mm->mmap_sem);
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has_write_lock = 1;
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goto retry;
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}
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mapping = vma->vm_file->f_mapping;
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/*
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* page_mkclean doesn't work on nonlinear vmas, so if
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* dirty pages need to be accounted, emulate with linear
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* vmas.
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*/
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if (mapping_cap_account_dirty(mapping)) {
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unsigned long addr;
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struct file *file = vma->vm_file;
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flags &= MAP_NONBLOCK;
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get_file(file);
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addr = mmap_region(file, start, size,
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flags, vma->vm_flags, pgoff);
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fput(file);
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if (IS_ERR_VALUE(addr)) {
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err = addr;
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} else {
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BUG_ON(addr != start);
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err = 0;
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}
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goto out;
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}
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spin_lock(&mapping->i_mmap_lock);
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flush_dcache_mmap_lock(mapping);
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vma->vm_flags |= VM_NONLINEAR;
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vma_prio_tree_remove(vma, &mapping->i_mmap);
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vma_nonlinear_insert(vma, &mapping->i_mmap_nonlinear);
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flush_dcache_mmap_unlock(mapping);
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spin_unlock(&mapping->i_mmap_lock);
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}
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if (vma->vm_flags & VM_LOCKED) {
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/*
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* drop PG_Mlocked flag for over-mapped range
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*/
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unsigned int saved_flags = vma->vm_flags;
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munlock_vma_pages_range(vma, start, start + size);
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vma->vm_flags = saved_flags;
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}
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mmu_notifier_invalidate_range_start(mm, start, start + size);
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err = populate_range(mm, vma, start, size, pgoff);
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mmu_notifier_invalidate_range_end(mm, start, start + size);
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if (!err && !(flags & MAP_NONBLOCK)) {
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if (vma->vm_flags & VM_LOCKED) {
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/*
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* might be mapping previously unmapped range of file
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*/
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mlock_vma_pages_range(vma, start, start + size);
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} else {
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if (unlikely(has_write_lock)) {
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downgrade_write(&mm->mmap_sem);
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has_write_lock = 0;
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}
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make_pages_present(start, start+size);
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}
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}
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/*
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* We can't clear VM_NONLINEAR because we'd have to do
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* it after ->populate completes, and that would prevent
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* downgrading the lock. (Locks can't be upgraded).
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*/
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out:
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if (likely(!has_write_lock))
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up_read(&mm->mmap_sem);
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else
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up_write(&mm->mmap_sem);
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return err;
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}
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