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thp: optimize away unnecessary page table locking
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Currently when we check if we can handle thp as it is or we need to split
it into regular sized pages, we hold page table lock prior to check
whether a given pmd is mapping thp or not.  Because of this, when it's not
"huge pmd" we suffer from unnecessary lock/unlock overhead.  To remove it,
this patch introduces a optimized check function and replace several
similar logics with it.

[akpm@linux-foundation.org: checkpatch fixes]
Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Naoya Horiguchi authored and Linus Torvalds committed Mar 22, 2012
1 parent 5aaabe8 commit 025c5b2
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Showing 3 changed files with 101 additions and 114 deletions.
73 changes: 25 additions & 48 deletions fs/proc/task_mmu.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -394,20 +394,11 @@ static int smaps_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
pte_t *pte;
spinlock_t *ptl;

spin_lock(&walk->mm->page_table_lock);
if (pmd_trans_huge(*pmd)) {
if (pmd_trans_splitting(*pmd)) {
spin_unlock(&walk->mm->page_table_lock);
wait_split_huge_page(vma->anon_vma, pmd);
} else {
smaps_pte_entry(*(pte_t *)pmd, addr,
HPAGE_PMD_SIZE, walk);
spin_unlock(&walk->mm->page_table_lock);
mss->anonymous_thp += HPAGE_PMD_SIZE;
return 0;
}
} else {
if (pmd_trans_huge_lock(pmd, vma) == 1) {
smaps_pte_entry(*(pte_t *)pmd, addr, HPAGE_PMD_SIZE, walk);
spin_unlock(&walk->mm->page_table_lock);
mss->anonymous_thp += HPAGE_PMD_SIZE;
return 0;
}

if (pmd_trans_unstable(pmd))
Expand Down Expand Up @@ -705,26 +696,19 @@ static int pagemap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
/* find the first VMA at or above 'addr' */
vma = find_vma(walk->mm, addr);
spin_lock(&walk->mm->page_table_lock);
if (pmd_trans_huge(*pmd)) {
if (pmd_trans_splitting(*pmd)) {
spin_unlock(&walk->mm->page_table_lock);
wait_split_huge_page(vma->anon_vma, pmd);
} else {
for (; addr != end; addr += PAGE_SIZE) {
unsigned long offset;

offset = (addr & ~PAGEMAP_WALK_MASK) >>
PAGE_SHIFT;
pfn = thp_pmd_to_pagemap_entry(*pmd, offset);
err = add_to_pagemap(addr, pfn, pm);
if (err)
break;
}
spin_unlock(&walk->mm->page_table_lock);
return err;
if (pmd_trans_huge_lock(pmd, vma) == 1) {
for (; addr != end; addr += PAGE_SIZE) {
unsigned long offset;

offset = (addr & ~PAGEMAP_WALK_MASK) >>
PAGE_SHIFT;
pfn = thp_pmd_to_pagemap_entry(*pmd, offset);
err = add_to_pagemap(addr, pfn, pm);
if (err)
break;
}
} else {
spin_unlock(&walk->mm->page_table_lock);
return err;
}

for (; addr != end; addr += PAGE_SIZE) {
Expand Down Expand Up @@ -992,24 +976,17 @@ static int gather_pte_stats(pmd_t *pmd, unsigned long addr,
pte_t *pte;

md = walk->private;
spin_lock(&walk->mm->page_table_lock);
if (pmd_trans_huge(*pmd)) {
if (pmd_trans_splitting(*pmd)) {
spin_unlock(&walk->mm->page_table_lock);
wait_split_huge_page(md->vma->anon_vma, pmd);
} else {
pte_t huge_pte = *(pte_t *)pmd;
struct page *page;

page = can_gather_numa_stats(huge_pte, md->vma, addr);
if (page)
gather_stats(page, md, pte_dirty(huge_pte),
HPAGE_PMD_SIZE/PAGE_SIZE);
spin_unlock(&walk->mm->page_table_lock);
return 0;
}
} else {

if (pmd_trans_huge_lock(pmd, md->vma) == 1) {
pte_t huge_pte = *(pte_t *)pmd;
struct page *page;

page = can_gather_numa_stats(huge_pte, md->vma, addr);
if (page)
gather_stats(page, md, pte_dirty(huge_pte),
HPAGE_PMD_SIZE/PAGE_SIZE);
spin_unlock(&walk->mm->page_table_lock);
return 0;
}

if (pmd_trans_unstable(pmd))
Expand Down
17 changes: 17 additions & 0 deletions include/linux/huge_mm.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -113,6 +113,18 @@ extern void __vma_adjust_trans_huge(struct vm_area_struct *vma,
unsigned long start,
unsigned long end,
long adjust_next);
extern int __pmd_trans_huge_lock(pmd_t *pmd,
struct vm_area_struct *vma);
/* mmap_sem must be held on entry */
static inline int pmd_trans_huge_lock(pmd_t *pmd,
struct vm_area_struct *vma)
{
VM_BUG_ON(!rwsem_is_locked(&vma->vm_mm->mmap_sem));
if (pmd_trans_huge(*pmd))
return __pmd_trans_huge_lock(pmd, vma);
else
return 0;
}
static inline void vma_adjust_trans_huge(struct vm_area_struct *vma,
unsigned long start,
unsigned long end,
Expand Down Expand Up @@ -176,6 +188,11 @@ static inline void vma_adjust_trans_huge(struct vm_area_struct *vma,
long adjust_next)
{
}
static inline int pmd_trans_huge_lock(pmd_t *pmd,
struct vm_area_struct *vma)
{
return 0;
}
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */

#endif /* _LINUX_HUGE_MM_H */
125 changes: 59 additions & 66 deletions mm/huge_memory.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1031,32 +1031,23 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
{
int ret = 0;

spin_lock(&tlb->mm->page_table_lock);
if (likely(pmd_trans_huge(*pmd))) {
if (unlikely(pmd_trans_splitting(*pmd))) {
spin_unlock(&tlb->mm->page_table_lock);
wait_split_huge_page(vma->anon_vma,
pmd);
} else {
struct page *page;
pgtable_t pgtable;
pgtable = get_pmd_huge_pte(tlb->mm);
page = pmd_page(*pmd);
pmd_clear(pmd);
tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
page_remove_rmap(page);
VM_BUG_ON(page_mapcount(page) < 0);
add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PMD_NR);
VM_BUG_ON(!PageHead(page));
tlb->mm->nr_ptes--;
spin_unlock(&tlb->mm->page_table_lock);
tlb_remove_page(tlb, page);
pte_free(tlb->mm, pgtable);
ret = 1;
}
} else
if (__pmd_trans_huge_lock(pmd, vma) == 1) {
struct page *page;
pgtable_t pgtable;
pgtable = get_pmd_huge_pte(tlb->mm);
page = pmd_page(*pmd);
pmd_clear(pmd);
tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
page_remove_rmap(page);
VM_BUG_ON(page_mapcount(page) < 0);
add_mm_counter(tlb->mm, MM_ANONPAGES, -HPAGE_PMD_NR);
VM_BUG_ON(!PageHead(page));
tlb->mm->nr_ptes--;
spin_unlock(&tlb->mm->page_table_lock);

tlb_remove_page(tlb, page);
pte_free(tlb->mm, pgtable);
ret = 1;
}
return ret;
}

Expand All @@ -1066,21 +1057,15 @@ int mincore_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
{
int ret = 0;

spin_lock(&vma->vm_mm->page_table_lock);
if (likely(pmd_trans_huge(*pmd))) {
ret = !pmd_trans_splitting(*pmd);
spin_unlock(&vma->vm_mm->page_table_lock);
if (unlikely(!ret))
wait_split_huge_page(vma->anon_vma, pmd);
else {
/*
* All logical pages in the range are present
* if backed by a huge page.
*/
memset(vec, 1, (end - addr) >> PAGE_SHIFT);
}
} else
if (__pmd_trans_huge_lock(pmd, vma) == 1) {
/*
* All logical pages in the range are present
* if backed by a huge page.
*/
spin_unlock(&vma->vm_mm->page_table_lock);
memset(vec, 1, (end - addr) >> PAGE_SHIFT);
ret = 1;
}

return ret;
}
Expand Down Expand Up @@ -1110,20 +1095,11 @@ int move_huge_pmd(struct vm_area_struct *vma, struct vm_area_struct *new_vma,
goto out;
}

spin_lock(&mm->page_table_lock);
if (likely(pmd_trans_huge(*old_pmd))) {
if (pmd_trans_splitting(*old_pmd)) {
spin_unlock(&mm->page_table_lock);
wait_split_huge_page(vma->anon_vma, old_pmd);
ret = -1;
} else {
pmd = pmdp_get_and_clear(mm, old_addr, old_pmd);
VM_BUG_ON(!pmd_none(*new_pmd));
set_pmd_at(mm, new_addr, new_pmd, pmd);
spin_unlock(&mm->page_table_lock);
ret = 1;
}
} else {
ret = __pmd_trans_huge_lock(old_pmd, vma);
if (ret == 1) {
pmd = pmdp_get_and_clear(mm, old_addr, old_pmd);
VM_BUG_ON(!pmd_none(*new_pmd));
set_pmd_at(mm, new_addr, new_pmd, pmd);
spin_unlock(&mm->page_table_lock);
}
out:
Expand All @@ -1136,24 +1112,41 @@ int change_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
struct mm_struct *mm = vma->vm_mm;
int ret = 0;

spin_lock(&mm->page_table_lock);
if (__pmd_trans_huge_lock(pmd, vma) == 1) {
pmd_t entry;
entry = pmdp_get_and_clear(mm, addr, pmd);
entry = pmd_modify(entry, newprot);
set_pmd_at(mm, addr, pmd, entry);
spin_unlock(&vma->vm_mm->page_table_lock);
ret = 1;
}

return ret;
}

/*
* Returns 1 if a given pmd maps a stable (not under splitting) thp.
* Returns -1 if it maps a thp under splitting. Returns 0 otherwise.
*
* Note that if it returns 1, this routine returns without unlocking page
* table locks. So callers must unlock them.
*/
int __pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma)
{
spin_lock(&vma->vm_mm->page_table_lock);
if (likely(pmd_trans_huge(*pmd))) {
if (unlikely(pmd_trans_splitting(*pmd))) {
spin_unlock(&mm->page_table_lock);
spin_unlock(&vma->vm_mm->page_table_lock);
wait_split_huge_page(vma->anon_vma, pmd);
return -1;
} else {
pmd_t entry;

entry = pmdp_get_and_clear(mm, addr, pmd);
entry = pmd_modify(entry, newprot);
set_pmd_at(mm, addr, pmd, entry);
spin_unlock(&vma->vm_mm->page_table_lock);
ret = 1;
/* Thp mapped by 'pmd' is stable, so we can
* handle it as it is. */
return 1;
}
} else
spin_unlock(&vma->vm_mm->page_table_lock);

return ret;
}
spin_unlock(&vma->vm_mm->page_table_lock);
return 0;
}

pmd_t *page_check_address_pmd(struct page *page,
Expand Down

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