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thp: rewrite freeze_page()/unfreeze_page() with generic rmap walkers
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freeze_page() and unfreeze_page() helpers evolved in rather complex
beasts.  It would be nice to cut complexity of this code.

This patch rewrites freeze_page() using standard try_to_unmap().
unfreeze_page() is rewritten with remove_migration_ptes().

The result is much simpler.

But the new variant is somewhat slower for PTE-mapped THPs.  Current
helpers iterates over VMAs the compound page is mapped to, and then over
ptes within this VMA.  New helpers iterates over small page, then over
VMA the small page mapped to, and only then find relevant pte.

We have short cut for PMD-mapped THP: we directly install migration
entries on PMD split.

I don't think the slowdown is critical, considering how much simpler
result is and that split_huge_page() is quite rare nowadays.  It only
happens due memory pressure or migration.

Signed-off-by: Kirill A. Shutemov <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
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@kiryl @torvalds
kiryl authored and torvalds committed Mar 17, 2016
1 parent e388466 commit fec89c1
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Showing 3 changed files with 50 additions and 180 deletions.
10 changes: 6 additions & 4 deletions include/linux/huge_mm.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -96,18 +96,20 @@ static inline int split_huge_page(struct page *page)
void deferred_split_huge_page(struct page *page);

void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
unsigned long address);
unsigned long address, bool freeze);

#define split_huge_pmd(__vma, __pmd, __address) \
do { \
pmd_t *____pmd = (__pmd); \
if (pmd_trans_huge(*____pmd) \
|| pmd_devmap(*____pmd)) \
__split_huge_pmd(__vma, __pmd, __address); \
__split_huge_pmd(__vma, __pmd, __address, \
false); \
} while (0)


void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address);
void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address,
bool freeze, struct page *page);

#if HPAGE_PMD_ORDER >= MAX_ORDER
#error "hugepages can't be allocated by the buddy allocator"
Expand Down Expand Up @@ -178,7 +180,7 @@ static inline void deferred_split_huge_page(struct page *page) {}
do { } while (0)

static inline void split_huge_pmd_address(struct vm_area_struct *vma,
unsigned long address) {}
unsigned long address, bool freeze, struct page *page) {}

static inline int hugepage_madvise(struct vm_area_struct *vma,
unsigned long *vm_flags, int advice)
Expand Down
210 changes: 36 additions & 174 deletions mm/huge_memory.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -2977,7 +2977,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
}

void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
unsigned long address)
unsigned long address, bool freeze)
{
spinlock_t *ptl;
struct mm_struct *mm = vma->vm_mm;
Expand All @@ -2994,7 +2994,7 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
page = NULL;
} else if (!pmd_devmap(*pmd))
goto out;
__split_huge_pmd_locked(vma, pmd, haddr, false);
__split_huge_pmd_locked(vma, pmd, haddr, freeze);
out:
spin_unlock(ptl);
mmu_notifier_invalidate_range_end(mm, haddr, haddr + HPAGE_PMD_SIZE);
Expand All @@ -3006,7 +3006,8 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
}
}

void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address)
void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address,
bool freeze, struct page *page)
{
pgd_t *pgd;
pud_t *pud;
Expand All @@ -3023,11 +3024,20 @@ void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address)
pmd = pmd_offset(pud, address);
if (!pmd_present(*pmd) || (!pmd_trans_huge(*pmd) && !pmd_devmap(*pmd)))
return;

/*
* If caller asks to setup a migration entries, we need a page to check
* pmd against. Otherwise we can end up replacing wrong page.
*/
VM_BUG_ON(freeze && !page);
if (page && page != pmd_page(*pmd))
return;

/*
* Caller holds the mmap_sem write mode, so a huge pmd cannot
* materialize from under us.
*/
split_huge_pmd(vma, pmd, address);
__split_huge_pmd(vma, pmd, address, freeze);
}

void vma_adjust_trans_huge(struct vm_area_struct *vma,
Expand All @@ -3043,7 +3053,7 @@ void vma_adjust_trans_huge(struct vm_area_struct *vma,
if (start & ~HPAGE_PMD_MASK &&
(start & HPAGE_PMD_MASK) >= vma->vm_start &&
(start & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
split_huge_pmd_address(vma, start);
split_huge_pmd_address(vma, start, false, NULL);

/*
* If the new end address isn't hpage aligned and it could
Expand All @@ -3053,7 +3063,7 @@ void vma_adjust_trans_huge(struct vm_area_struct *vma,
if (end & ~HPAGE_PMD_MASK &&
(end & HPAGE_PMD_MASK) >= vma->vm_start &&
(end & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= vma->vm_end)
split_huge_pmd_address(vma, end);
split_huge_pmd_address(vma, end, false, NULL);

/*
* If we're also updating the vma->vm_next->vm_start, if the new
Expand All @@ -3067,184 +3077,36 @@ void vma_adjust_trans_huge(struct vm_area_struct *vma,
if (nstart & ~HPAGE_PMD_MASK &&
(nstart & HPAGE_PMD_MASK) >= next->vm_start &&
(nstart & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE <= next->vm_end)
split_huge_pmd_address(next, nstart);
split_huge_pmd_address(next, nstart, false, NULL);
}
}

static void freeze_page_vma(struct vm_area_struct *vma, struct page *page,
unsigned long address)
static void freeze_page(struct page *page)
{
unsigned long haddr = address & HPAGE_PMD_MASK;
spinlock_t *ptl;
pgd_t *pgd;
pud_t *pud;
pmd_t *pmd;
pte_t *pte;
int i, nr = HPAGE_PMD_NR;

/* Skip pages which doesn't belong to the VMA */
if (address < vma->vm_start) {
int off = (vma->vm_start - address) >> PAGE_SHIFT;
page += off;
nr -= off;
address = vma->vm_start;
}

pgd = pgd_offset(vma->vm_mm, address);
if (!pgd_present(*pgd))
return;
pud = pud_offset(pgd, address);
if (!pud_present(*pud))
return;
pmd = pmd_offset(pud, address);
ptl = pmd_lock(vma->vm_mm, pmd);
if (!pmd_present(*pmd)) {
spin_unlock(ptl);
return;
}
if (pmd_trans_huge(*pmd)) {
if (page == pmd_page(*pmd))
__split_huge_pmd_locked(vma, pmd, haddr, true);
spin_unlock(ptl);
return;
}
spin_unlock(ptl);

pte = pte_offset_map_lock(vma->vm_mm, pmd, address, &ptl);
for (i = 0; i < nr; i++, address += PAGE_SIZE, page++, pte++) {
pte_t entry, swp_pte;
swp_entry_t swp_entry;

/*
* We've just crossed page table boundary: need to map next one.
* It can happen if THP was mremaped to non PMD-aligned address.
*/
if (unlikely(address == haddr + HPAGE_PMD_SIZE)) {
pte_unmap_unlock(pte - 1, ptl);
pmd = mm_find_pmd(vma->vm_mm, address);
if (!pmd)
return;
pte = pte_offset_map_lock(vma->vm_mm, pmd,
address, &ptl);
}

if (!pte_present(*pte))
continue;
if (page_to_pfn(page) != pte_pfn(*pte))
continue;
flush_cache_page(vma, address, page_to_pfn(page));
entry = ptep_clear_flush(vma, address, pte);
if (pte_dirty(entry))
SetPageDirty(page);
swp_entry = make_migration_entry(page, pte_write(entry));
swp_pte = swp_entry_to_pte(swp_entry);
if (pte_soft_dirty(entry))
swp_pte = pte_swp_mksoft_dirty(swp_pte);
set_pte_at(vma->vm_mm, address, pte, swp_pte);
page_remove_rmap(page, false);
put_page(page);
}
pte_unmap_unlock(pte - 1, ptl);
}

static void freeze_page(struct anon_vma *anon_vma, struct page *page)
{
struct anon_vma_chain *avc;
pgoff_t pgoff = page_to_pgoff(page);
enum ttu_flags ttu_flags = TTU_MIGRATION | TTU_IGNORE_MLOCK |
TTU_IGNORE_ACCESS | TTU_RMAP_LOCKED;
int i, ret;

VM_BUG_ON_PAGE(!PageHead(page), page);

anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root, pgoff,
pgoff + HPAGE_PMD_NR - 1) {
unsigned long address = __vma_address(page, avc->vma);

mmu_notifier_invalidate_range_start(avc->vma->vm_mm,
address, address + HPAGE_PMD_SIZE);
freeze_page_vma(avc->vma, page, address);
mmu_notifier_invalidate_range_end(avc->vma->vm_mm,
address, address + HPAGE_PMD_SIZE);
}
}

static void unfreeze_page_vma(struct vm_area_struct *vma, struct page *page,
unsigned long address)
{
spinlock_t *ptl;
pmd_t *pmd;
pte_t *pte, entry;
swp_entry_t swp_entry;
unsigned long haddr = address & HPAGE_PMD_MASK;
int i, nr = HPAGE_PMD_NR;

/* Skip pages which doesn't belong to the VMA */
if (address < vma->vm_start) {
int off = (vma->vm_start - address) >> PAGE_SHIFT;
page += off;
nr -= off;
address = vma->vm_start;
}

pmd = mm_find_pmd(vma->vm_mm, address);
if (!pmd)
return;

pte = pte_offset_map_lock(vma->vm_mm, pmd, address, &ptl);
for (i = 0; i < nr; i++, address += PAGE_SIZE, page++, pte++) {
/*
* We've just crossed page table boundary: need to map next one.
* It can happen if THP was mremaped to non-PMD aligned address.
*/
if (unlikely(address == haddr + HPAGE_PMD_SIZE)) {
pte_unmap_unlock(pte - 1, ptl);
pmd = mm_find_pmd(vma->vm_mm, address);
if (!pmd)
return;
pte = pte_offset_map_lock(vma->vm_mm, pmd,
address, &ptl);
}

if (!is_swap_pte(*pte))
continue;

swp_entry = pte_to_swp_entry(*pte);
if (!is_migration_entry(swp_entry))
continue;
if (migration_entry_to_page(swp_entry) != page)
continue;

get_page(page);
page_add_anon_rmap(page, vma, address, false);

entry = pte_mkold(mk_pte(page, vma->vm_page_prot));
if (PageDirty(page))
entry = pte_mkdirty(entry);
if (is_write_migration_entry(swp_entry))
entry = maybe_mkwrite(entry, vma);

flush_dcache_page(page);
set_pte_at(vma->vm_mm, address, pte, entry);
/* We only need TTU_SPLIT_HUGE_PMD once */
ret = try_to_unmap(page, ttu_flags | TTU_SPLIT_HUGE_PMD);
for (i = 1; !ret && i < HPAGE_PMD_NR; i++) {
/* Cut short if the page is unmapped */
if (page_count(page) == 1)
return;

/* No need to invalidate - it was non-present before */
update_mmu_cache(vma, address, pte);
ret = try_to_unmap(page + i, ttu_flags);
}
pte_unmap_unlock(pte - 1, ptl);
VM_BUG_ON(ret);
}

static void unfreeze_page(struct anon_vma *anon_vma, struct page *page)
static void unfreeze_page(struct page *page)
{
struct anon_vma_chain *avc;
pgoff_t pgoff = page_to_pgoff(page);

anon_vma_interval_tree_foreach(avc, &anon_vma->rb_root,
pgoff, pgoff + HPAGE_PMD_NR - 1) {
unsigned long address = __vma_address(page, avc->vma);
int i;

mmu_notifier_invalidate_range_start(avc->vma->vm_mm,
address, address + HPAGE_PMD_SIZE);
unfreeze_page_vma(avc->vma, page, address);
mmu_notifier_invalidate_range_end(avc->vma->vm_mm,
address, address + HPAGE_PMD_SIZE);
}
for (i = 0; i < HPAGE_PMD_NR; i++)
remove_migration_ptes(page + i, page + i, true);
}

static void __split_huge_page_tail(struct page *head, int tail,
Expand Down Expand Up @@ -3322,7 +3184,7 @@ static void __split_huge_page(struct page *page, struct list_head *list)
ClearPageCompound(head);
spin_unlock_irq(&zone->lru_lock);

unfreeze_page(page_anon_vma(head), head);
unfreeze_page(head);

for (i = 0; i < HPAGE_PMD_NR; i++) {
struct page *subpage = head + i;
Expand Down Expand Up @@ -3418,7 +3280,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
}

mlocked = PageMlocked(page);
freeze_page(anon_vma, head);
freeze_page(head);
VM_BUG_ON_PAGE(compound_mapcount(head), head);

/* Make sure the page is not on per-CPU pagevec as it takes pin */
Expand Down Expand Up @@ -3447,7 +3309,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
BUG();
} else {
spin_unlock_irqrestore(&pgdata->split_queue_lock, flags);
unfreeze_page(anon_vma, head);
unfreeze_page(head);
ret = -EBUSY;
}

Expand Down
10 changes: 8 additions & 2 deletions mm/rmap.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1431,8 +1431,14 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
if ((flags & TTU_MUNLOCK) && !(vma->vm_flags & VM_LOCKED))
goto out;

if (flags & TTU_SPLIT_HUGE_PMD)
split_huge_pmd_address(vma, address);
if (flags & TTU_SPLIT_HUGE_PMD) {
split_huge_pmd_address(vma, address,
flags & TTU_MIGRATION, page);
/* check if we have anything to do after split */
if (page_mapcount(page) == 0)
goto out;
}

pte = page_check_address(page, mm, address, &ptl, 0);
if (!pte)
goto out;
Expand Down

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