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khugepaged: allow to collapse PTE-mapped compound pages
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We can collapse PTE-mapped compound pages.  We only need to avoid handling
them more than once: lock/unlock page only once if it's present in the PMD
range multiple times as it handled on compound level.  The same goes for
LRU isolation and putback.

Signed-off-by: Kirill A. Shutemov <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Tested-by: Zi Yan <[email protected]>
Reviewed-by: William Kucharski <[email protected]>
Reviewed-by: Zi Yan <[email protected]>
Acked-by: Yang Shi <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: John Hubbard <[email protected]>
Cc: Mike Kravetz <[email protected]>
Cc: Ralph Campbell <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Linus Torvalds <[email protected]>
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@kiryl @torvalds
kiryl authored and torvalds committed Jun 4, 2020
1 parent 9445689 commit 5503fbf
Showing 1 changed file with 65 additions and 34 deletions.
99 changes: 65 additions & 34 deletions mm/khugepaged.c
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Original file line number Diff line number Diff line change
Expand Up @@ -512,17 +512,30 @@ void __khugepaged_exit(struct mm_struct *mm)

static void release_pte_page(struct page *page)
{
dec_node_page_state(page, NR_ISOLATED_ANON + page_is_file_lru(page));
mod_node_page_state(page_pgdat(page),
NR_ISOLATED_ANON + page_is_file_lru(page),
-compound_nr(page));
unlock_page(page);
putback_lru_page(page);
}

static void release_pte_pages(pte_t *pte, pte_t *_pte)
static void release_pte_pages(pte_t *pte, pte_t *_pte,
struct list_head *compound_pagelist)
{
struct page *page, *tmp;

while (--_pte >= pte) {
pte_t pteval = *_pte;
if (!pte_none(pteval) && !is_zero_pfn(pte_pfn(pteval)))
release_pte_page(pte_page(pteval));

page = pte_page(pteval);
if (!pte_none(pteval) && !is_zero_pfn(pte_pfn(pteval)) &&
!PageCompound(page))
release_pte_page(page);
}

list_for_each_entry_safe(page, tmp, compound_pagelist, lru) {
list_del(&page->lru);
release_pte_page(page);
}
}

Expand All @@ -539,7 +552,8 @@ static bool is_refcount_suitable(struct page *page)

static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
unsigned long address,
pte_t *pte)
pte_t *pte,
struct list_head *compound_pagelist)
{
struct page *page = NULL;
pte_t *_pte;
Expand Down Expand Up @@ -569,13 +583,21 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
goto out;
}

/* TODO: teach khugepaged to collapse THP mapped with pte */
VM_BUG_ON_PAGE(!PageAnon(page), page);

if (PageCompound(page)) {
result = SCAN_PAGE_COMPOUND;
goto out;
}
struct page *p;
page = compound_head(page);

VM_BUG_ON_PAGE(!PageAnon(page), page);
/*
* Check if we have dealt with the compound page
* already
*/
list_for_each_entry(p, compound_pagelist, lru) {
if (page == p)
goto next;
}
}

/*
* We can do it before isolate_lru_page because the
Expand Down Expand Up @@ -604,19 +626,15 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
result = SCAN_PAGE_COUNT;
goto out;
}
if (pte_write(pteval)) {
writable = true;
} else {
if (PageSwapCache(page) &&
!reuse_swap_page(page, NULL)) {
unlock_page(page);
result = SCAN_SWAP_CACHE_PAGE;
goto out;
}
if (!pte_write(pteval) && PageSwapCache(page) &&
!reuse_swap_page(page, NULL)) {
/*
* Page is not in the swap cache. It can be collapsed
* into a THP.
* Page is in the swap cache and cannot be re-used.
* It cannot be collapsed into a THP.
*/
unlock_page(page);
result = SCAN_SWAP_CACHE_PAGE;
goto out;
}

/*
Expand All @@ -628,16 +646,23 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
result = SCAN_DEL_PAGE_LRU;
goto out;
}
inc_node_page_state(page,
NR_ISOLATED_ANON + page_is_file_lru(page));
mod_node_page_state(page_pgdat(page),
NR_ISOLATED_ANON + page_is_file_lru(page),
compound_nr(page));
VM_BUG_ON_PAGE(!PageLocked(page), page);
VM_BUG_ON_PAGE(PageLRU(page), page);

if (PageCompound(page))
list_add_tail(&page->lru, compound_pagelist);
next:
/* There should be enough young pte to collapse the page */
if (pte_young(pteval) ||
page_is_young(page) || PageReferenced(page) ||
mmu_notifier_test_young(vma->vm_mm, address))
referenced++;

if (pte_write(pteval))
writable = true;
}
if (likely(writable)) {
if (likely(referenced)) {
Expand All @@ -651,7 +676,7 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
}

out:
release_pte_pages(pte, _pte);
release_pte_pages(pte, _pte, compound_pagelist);
trace_mm_collapse_huge_page_isolate(page, none_or_zero,
referenced, writable, result);
return 0;
Expand All @@ -660,13 +685,14 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
struct vm_area_struct *vma,
unsigned long address,
spinlock_t *ptl)
spinlock_t *ptl,
struct list_head *compound_pagelist)
{
struct page *src_page, *tmp;
pte_t *_pte;
for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
_pte++, page++, address += PAGE_SIZE) {
pte_t pteval = *_pte;
struct page *src_page;

if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
clear_user_highpage(page, address);
Expand All @@ -686,7 +712,8 @@ static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
} else {
src_page = pte_page(pteval);
copy_user_highpage(page, src_page, address, vma);
release_pte_page(src_page);
if (!PageCompound(src_page))
release_pte_page(src_page);
/*
* ptl mostly unnecessary, but preempt has to
* be disabled to update the per-cpu stats
Expand All @@ -703,6 +730,11 @@ static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
free_page_and_swap_cache(src_page);
}
}

list_for_each_entry_safe(src_page, tmp, compound_pagelist, lru) {
list_del(&src_page->lru);
release_pte_page(src_page);
}
}

static void khugepaged_alloc_sleep(void)
Expand Down Expand Up @@ -961,6 +993,7 @@ static void collapse_huge_page(struct mm_struct *mm,
struct page **hpage,
int node, int referenced, int unmapped)
{
LIST_HEAD(compound_pagelist);
pmd_t *pmd, _pmd;
pte_t *pte;
pgtable_t pgtable;
Expand Down Expand Up @@ -1061,7 +1094,8 @@ static void collapse_huge_page(struct mm_struct *mm,
mmu_notifier_invalidate_range_end(&range);

spin_lock(pte_ptl);
isolated = __collapse_huge_page_isolate(vma, address, pte);
isolated = __collapse_huge_page_isolate(vma, address, pte,
&compound_pagelist);
spin_unlock(pte_ptl);

if (unlikely(!isolated)) {
Expand All @@ -1086,7 +1120,8 @@ static void collapse_huge_page(struct mm_struct *mm,
*/
anon_vma_unlock_write(vma->anon_vma);

__collapse_huge_page_copy(pte, new_page, vma, address, pte_ptl);
__collapse_huge_page_copy(pte, new_page, vma, address, pte_ptl,
&compound_pagelist);
pte_unmap(pte);
__SetPageUptodate(new_page);
pgtable = pmd_pgtable(_pmd);
Expand Down Expand Up @@ -1205,11 +1240,7 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
goto out_unmap;
}

/* TODO: teach khugepaged to collapse THP mapped with pte */
if (PageCompound(page)) {
result = SCAN_PAGE_COMPOUND;
goto out_unmap;
}
page = compound_head(page);

/*
* Record which node the original page is from and save this
Expand Down

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