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Commit b9773199 authored by Kirill A. Shutemov's avatar Kirill A. Shutemov Committed by Linus Torvalds
Browse files

rmap: introduce rmap_walk_locked() 



This patchset rewrites freeze_page() and unfreeze_page() using
try_to_unmap() and remove_migration_ptes().  Result is much simpler, but
somewhat slower.

Migration 8GiB worth of PMD-mapped THP:

  Baseline	20.21 +/- 0.393
  Patched	20.73 +/- 0.082
  Slowdown	1.03x

It's 3% slower, comparing to 14% in v1.  I don't it should be a stopper.

Splitting of PTE-mapped pages slowed more.  But this is not a common
case.

Migration 8GiB worth of PMD-mapped THP:

  Baseline	20.39 +/- 0.225
  Patched	22.43 +/- 0.496
  Slowdown	1.10x

rmap_walk_locked() is the same as rmap_walk(), but the caller takes care
of the relevant rmap lock.

This is preparation for switching THP splitting from custom rmap walk in
freeze_page()/unfreeze_page() to the generic one.

There is no support for KSM pages for now: not clear which lock is
implied.

Signed-off-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 99490f16

include/linux/rmap.h

+1 −0
Original line number Diff line number Diff line
@@ -266,6 +266,7 @@ struct rmap_walk_control { 
};



int rmap_walk(struct page *page, struct rmap_walk_control *rwc);

int rmap_walk_locked(struct page *page, struct rmap_walk_control *rwc);



#else	/* !CONFIG_MMU */

mm/rmap.c

+32 −9
Original line number Diff line number Diff line
@@ -1715,14 +1715,21 @@ static struct anon_vma *rmap_walk_anon_lock(struct page *page, 
 * vm_flags for that VMA.  That should be OK, because that vma shouldn't be

 * LOCKED.

 */

static int rmap_walk_anon(struct page *page, struct rmap_walk_control *rwc)

static int rmap_walk_anon(struct page *page, struct rmap_walk_control *rwc,

		bool locked)

{

	struct anon_vma *anon_vma;

	pgoff_t pgoff;

	struct anon_vma_chain *avc;

	int ret = SWAP_AGAIN;



	if (locked) {

		anon_vma = page_anon_vma(page);

		/* anon_vma disappear under us? */

		VM_BUG_ON_PAGE(!anon_vma, page);

	} else {

		anon_vma = rmap_walk_anon_lock(page, rwc);

	}

	if (!anon_vma)

		return ret;
@@ -1742,6 +1749,8 @@ static int rmap_walk_anon(struct page *page, struct rmap_walk_control *rwc) 
		if (rwc->done && rwc->done(page))

			break;

	}



	if (!locked)

		anon_vma_unlock_read(anon_vma);

	return ret;

}
@@ -1759,9 +1768,10 @@ static int rmap_walk_anon(struct page *page, struct rmap_walk_control *rwc) 
 * vm_flags for that VMA.  That should be OK, because that vma shouldn't be

 * LOCKED.

 */

static int rmap_walk_file(struct page *page, struct rmap_walk_control *rwc)

static int rmap_walk_file(struct page *page, struct rmap_walk_control *rwc,

		bool locked)

{

	struct address_space *mapping = page->mapping;

	struct address_space *mapping = page_mapping(page);

	pgoff_t pgoff;

	struct vm_area_struct *vma;

	int ret = SWAP_AGAIN;
@@ -1778,6 +1788,7 @@ static int rmap_walk_file(struct page *page, struct rmap_walk_control *rwc) 
		return ret;



	pgoff = page_to_pgoff(page);

	if (!locked)

		i_mmap_lock_read(mapping);

	vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {

		unsigned long address = vma_address(page, vma);
@@ -1795,6 +1806,7 @@ static int rmap_walk_file(struct page *page, struct rmap_walk_control *rwc) 
	}



done:

	if (!locked)

		i_mmap_unlock_read(mapping);

	return ret;

}
@@ -1804,9 +1816,20 @@ int rmap_walk(struct page *page, struct rmap_walk_control *rwc) 
	if (unlikely(PageKsm(page)))

		return rmap_walk_ksm(page, rwc);

	else if (PageAnon(page))

		return rmap_walk_anon(page, rwc);

		return rmap_walk_anon(page, rwc, false);

	else

		return rmap_walk_file(page, rwc, false);

}



/* Like rmap_walk, but caller holds relevant rmap lock */

int rmap_walk_locked(struct page *page, struct rmap_walk_control *rwc)

{

	/* no ksm support for now */

	VM_BUG_ON_PAGE(PageKsm(page), page);

	if (PageAnon(page))

		return rmap_walk_anon(page, rwc, true);

	else

		return rmap_walk_file(page, rwc);

		return rmap_walk_file(page, rwc, true);

}



#ifdef CONFIG_HUGETLB_PAGE