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[PATCH] mm: follow_page with inner ptlock
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Final step in pushing down common core's page_table_lock.  follow_page no
longer wants caller to hold page_table_lock, uses pte_offset_map_lock itself;
and so no page_table_lock is taken in get_user_pages itself.

But get_user_pages (and get_futex_key) do then need follow_page to pin the
page for them: take Daniel's suggestion of bitflags to follow_page.

Need one for WRITE, another for TOUCH (it was the accessed flag before:
vanished along with check_user_page_readable, but surely get_numa_maps is
wrong to mark every page it finds as accessed), another for GET.

And another, ANON to dispose of untouched_anonymous_page: it seems silly for
that to descend a second time, let follow_page observe if there was no page
table and return ZERO_PAGE if so.  Fix minor bug in that: check VM_LOCKED -
make_pages_present ought to make readonly anonymous present.

Give get_numa_maps a cond_resched while we're there.

Signed-off-by: Hugh Dickins <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
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Hugh Dickins authored and Linus Torvalds committed Oct 30, 2005
1 parent c34d1b4 commit deceb6c
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Showing 5 changed files with 88 additions and 96 deletions.
3 changes: 1 addition & 2 deletions fs/proc/task_mmu.c
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Original file line number Diff line number Diff line change
Expand Up @@ -419,7 +419,6 @@ static struct numa_maps *get_numa_maps(const struct vm_area_struct *vma)
for_each_node(i)
md->node[i] =0;

spin_lock(&mm->page_table_lock);
for (vaddr = vma->vm_start; vaddr < vma->vm_end; vaddr += PAGE_SIZE) {
page = follow_page(mm, vaddr, 0);
if (page) {
Expand All @@ -434,8 +433,8 @@ static struct numa_maps *get_numa_maps(const struct vm_area_struct *vma)
md->anon++;
md->node[page_to_nid(page)]++;
}
cond_resched();
}
spin_unlock(&mm->page_table_lock);
return md;
}

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20 changes: 12 additions & 8 deletions include/linux/mm.h
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Original file line number Diff line number Diff line change
Expand Up @@ -938,14 +938,18 @@ static inline unsigned long vma_pages(struct vm_area_struct *vma)
return (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
}

extern struct vm_area_struct *find_extend_vma(struct mm_struct *mm, unsigned long addr);

extern struct page * vmalloc_to_page(void *addr);
extern unsigned long vmalloc_to_pfn(void *addr);
extern struct page * follow_page(struct mm_struct *mm, unsigned long address,
int write);
int remap_pfn_range(struct vm_area_struct *, unsigned long,
unsigned long, unsigned long, pgprot_t);
struct vm_area_struct *find_extend_vma(struct mm_struct *, unsigned long addr);
struct page *vmalloc_to_page(void *addr);
unsigned long vmalloc_to_pfn(void *addr);
int remap_pfn_range(struct vm_area_struct *, unsigned long addr,
unsigned long pfn, unsigned long size, pgprot_t);

struct page *follow_page(struct mm_struct *, unsigned long address,
unsigned int foll_flags);
#define FOLL_WRITE 0x01 /* check pte is writable */
#define FOLL_TOUCH 0x02 /* mark page accessed */
#define FOLL_GET 0x04 /* do get_page on page */
#define FOLL_ANON 0x08 /* give ZERO_PAGE if no pgtable */

#ifdef CONFIG_PROC_FS
void vm_stat_account(struct mm_struct *, unsigned long, struct file *, long);
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6 changes: 2 additions & 4 deletions kernel/futex.c
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Original file line number Diff line number Diff line change
Expand Up @@ -205,15 +205,13 @@ static int get_futex_key(unsigned long uaddr, union futex_key *key)
/*
* Do a quick atomic lookup first - this is the fastpath.
*/
spin_lock(&current->mm->page_table_lock);
page = follow_page(mm, uaddr, 0);
page = follow_page(mm, uaddr, FOLL_TOUCH|FOLL_GET);
if (likely(page != NULL)) {
key->shared.pgoff =
page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
spin_unlock(&current->mm->page_table_lock);
put_page(page);
return 0;
}
spin_unlock(&current->mm->page_table_lock);

/*
* Do it the general way.
Expand Down
152 changes: 71 additions & 81 deletions mm/memory.c
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Original file line number Diff line number Diff line change
Expand Up @@ -807,105 +807,102 @@ unsigned long zap_page_range(struct vm_area_struct *vma, unsigned long address,

/*
* Do a quick page-table lookup for a single page.
* mm->page_table_lock must be held.
*/
struct page *follow_page(struct mm_struct *mm, unsigned long address, int write)
struct page *follow_page(struct mm_struct *mm, unsigned long address,
unsigned int flags)
{
pgd_t *pgd;
pud_t *pud;
pmd_t *pmd;
pte_t *ptep, pte;
spinlock_t *ptl;
unsigned long pfn;
struct page *page;

page = follow_huge_addr(mm, address, write);
if (! IS_ERR(page))
return page;
page = follow_huge_addr(mm, address, flags & FOLL_WRITE);
if (!IS_ERR(page)) {
BUG_ON(flags & FOLL_GET);
goto out;
}

page = NULL;
pgd = pgd_offset(mm, address);
if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
goto out;
goto no_page_table;

pud = pud_offset(pgd, address);
if (pud_none(*pud) || unlikely(pud_bad(*pud)))
goto out;
goto no_page_table;

pmd = pmd_offset(pud, address);
if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
goto no_page_table;

if (pmd_huge(*pmd)) {
BUG_ON(flags & FOLL_GET);
page = follow_huge_pmd(mm, address, pmd, flags & FOLL_WRITE);
goto out;
if (pmd_huge(*pmd))
return follow_huge_pmd(mm, address, pmd, write);
}

ptep = pte_offset_map(pmd, address);
ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
if (!ptep)
goto out;

pte = *ptep;
pte_unmap(ptep);
if (pte_present(pte)) {
if (write && !pte_write(pte))
goto out;
pfn = pte_pfn(pte);
if (pfn_valid(pfn)) {
page = pfn_to_page(pfn);
if (write && !pte_dirty(pte) &&!PageDirty(page))
set_page_dirty(page);
mark_page_accessed(page);
return page;
}
}
if (!pte_present(pte))
goto unlock;
if ((flags & FOLL_WRITE) && !pte_write(pte))
goto unlock;
pfn = pte_pfn(pte);
if (!pfn_valid(pfn))
goto unlock;

page = pfn_to_page(pfn);
if (flags & FOLL_GET)
get_page(page);
if (flags & FOLL_TOUCH) {
if ((flags & FOLL_WRITE) &&
!pte_dirty(pte) && !PageDirty(page))
set_page_dirty(page);
mark_page_accessed(page);
}
unlock:
pte_unmap_unlock(ptep, ptl);
out:
return NULL;
}

static inline int
untouched_anonymous_page(struct mm_struct* mm, struct vm_area_struct *vma,
unsigned long address)
{
pgd_t *pgd;
pud_t *pud;
pmd_t *pmd;

/* Check if the vma is for an anonymous mapping. */
if (vma->vm_ops && vma->vm_ops->nopage)
return 0;

/* Check if page directory entry exists. */
pgd = pgd_offset(mm, address);
if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
return 1;

pud = pud_offset(pgd, address);
if (pud_none(*pud) || unlikely(pud_bad(*pud)))
return 1;

/* Check if page middle directory entry exists. */
pmd = pmd_offset(pud, address);
if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
return 1;
return page;

/* There is a pte slot for 'address' in 'mm'. */
return 0;
no_page_table:
/*
* When core dumping an enormous anonymous area that nobody
* has touched so far, we don't want to allocate page tables.
*/
if (flags & FOLL_ANON) {
page = ZERO_PAGE(address);
if (flags & FOLL_GET)
get_page(page);
BUG_ON(flags & FOLL_WRITE);
}
return page;
}

int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
unsigned long start, int len, int write, int force,
struct page **pages, struct vm_area_struct **vmas)
{
int i;
unsigned int flags;
unsigned int vm_flags;

/*
* Require read or write permissions.
* If 'force' is set, we only require the "MAY" flags.
*/
flags = write ? (VM_WRITE | VM_MAYWRITE) : (VM_READ | VM_MAYREAD);
flags &= force ? (VM_MAYREAD | VM_MAYWRITE) : (VM_READ | VM_WRITE);
vm_flags = write ? (VM_WRITE | VM_MAYWRITE) : (VM_READ | VM_MAYREAD);
vm_flags &= force ? (VM_MAYREAD | VM_MAYWRITE) : (VM_READ | VM_WRITE);
i = 0;

do {
struct vm_area_struct * vma;
struct vm_area_struct *vma;
unsigned int foll_flags;

vma = find_extend_vma(mm, start);
if (!vma && in_gate_area(tsk, start)) {
Expand Down Expand Up @@ -946,45 +943,41 @@ int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
}

if (!vma || (vma->vm_flags & (VM_IO | VM_RESERVED))
|| !(flags & vma->vm_flags))
|| !(vm_flags & vma->vm_flags))
return i ? : -EFAULT;

if (is_vm_hugetlb_page(vma)) {
i = follow_hugetlb_page(mm, vma, pages, vmas,
&start, &len, i);
continue;
}
spin_lock(&mm->page_table_lock);

foll_flags = FOLL_TOUCH;
if (pages)
foll_flags |= FOLL_GET;
if (!write && !(vma->vm_flags & VM_LOCKED) &&
(!vma->vm_ops || !vma->vm_ops->nopage))
foll_flags |= FOLL_ANON;

do {
int write_access = write;
struct page *page;

cond_resched_lock(&mm->page_table_lock);
while (!(page = follow_page(mm, start, write_access))) {
int ret;

/*
* Shortcut for anonymous pages. We don't want
* to force the creation of pages tables for
* insanely big anonymously mapped areas that
* nobody touched so far. This is important
* for doing a core dump for these mappings.
*/
if (!write && untouched_anonymous_page(mm,vma,start)) {
page = ZERO_PAGE(start);
break;
}
spin_unlock(&mm->page_table_lock);
ret = __handle_mm_fault(mm, vma, start, write_access);
if (write)
foll_flags |= FOLL_WRITE;

cond_resched();
while (!(page = follow_page(mm, start, foll_flags))) {
int ret;
ret = __handle_mm_fault(mm, vma, start,
foll_flags & FOLL_WRITE);
/*
* The VM_FAULT_WRITE bit tells us that do_wp_page has
* broken COW when necessary, even if maybe_mkwrite
* decided not to set pte_write. We can thus safely do
* subsequent page lookups as if they were reads.
*/
if (ret & VM_FAULT_WRITE)
write_access = 0;
foll_flags &= ~FOLL_WRITE;

switch (ret & ~VM_FAULT_WRITE) {
case VM_FAULT_MINOR:
Expand All @@ -1000,20 +993,17 @@ int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
default:
BUG();
}
spin_lock(&mm->page_table_lock);
}
if (pages) {
pages[i] = page;
flush_dcache_page(page);
page_cache_get(page);
}
if (vmas)
vmas[i] = vma;
i++;
start += PAGE_SIZE;
len--;
} while (len && start < vma->vm_end);
spin_unlock(&mm->page_table_lock);
} while (len);
return i;
}
Expand Down
3 changes: 2 additions & 1 deletion mm/nommu.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1049,7 +1049,8 @@ struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr)

EXPORT_SYMBOL(find_vma);

struct page * follow_page(struct mm_struct *mm, unsigned long addr, int write)
struct page *follow_page(struct mm_struct *mm, unsigned long address,
unsigned int foll_flags)
{
return NULL;
}
Expand Down

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