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Commit 7db7671f authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
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mm: page migration trylock newpage at same level as oldpage 



Clean up page migration a little by moving the trylock of newpage from
move_to_new_page() into __unmap_and_move(), where the old page has been
locked.  Adjust unmap_and_move_huge_page() and balloon_page_migrate()
accordingly.

But make one kind-of-functional change on the way: whereas trylock of
newpage used to BUG() if it failed, now simply return -EAGAIN if so.
Cutting out BUG()s is good, right?  But, to be honest, this is really to
extend the usefulness of the custom put_new_page feature, allowing a pool
of new pages to be shared perhaps with racing uses.

Use an "else" instead of that "skip_unmap" label.

Signed-off-by: default avatarHugh Dickins <hughd@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Acked-by: default avatarRafael Aquini <aquini@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 2def7424

mm/balloon_compaction.c

+2 −8
Original line number Diff line number Diff line
@@ -199,23 +199,17 @@ int balloon_page_migrate(struct page *newpage, 
	struct balloon_dev_info *balloon = balloon_page_device(page);

	int rc = -EAGAIN;



	/*

	 * Block others from accessing the 'newpage' when we get around to

	 * establishing additional references. We should be the only one

	 * holding a reference to the 'newpage' at this point.

	 */

	BUG_ON(!trylock_page(newpage));

	VM_BUG_ON_PAGE(!PageLocked(page), page);

	VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);



	if (WARN_ON(!__is_movable_balloon_page(page))) {

		dump_page(page, "not movable balloon page");

		unlock_page(newpage);

		return rc;

	}



	if (balloon && balloon->migratepage)

		rc = balloon->migratepage(balloon, newpage, page, mode);



	unlock_page(newpage);

	return rc;

}

#endif /* CONFIG_BALLOON_COMPACTION */

mm/migrate.c

+26 −20
Original line number Diff line number Diff line
@@ -727,13 +727,8 @@ static int move_to_new_page(struct page *newpage, struct page *page, 
	struct address_space *mapping;

	int rc;



	/*

	 * Block others from accessing the page when we get around to

	 * establishing additional references. We are the only one

	 * holding a reference to the new page at this point.

	 */

	if (!trylock_page(newpage))

		BUG();

	VM_BUG_ON_PAGE(!PageLocked(page), page);

	VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);



	/* Prepare mapping for the new page.*/

	newpage->index = page->index;
@@ -774,9 +769,6 @@ static int move_to_new_page(struct page *newpage, struct page *page, 
			remove_migration_ptes(page, newpage);

		page->mapping = NULL;

	}



	unlock_page(newpage);



	return rc;

}
@@ -861,6 +853,17 @@ static int __unmap_and_move(struct page *page, struct page *newpage, 
		}

	}



	/*

	 * Block others from accessing the new page when we get around to

	 * establishing additional references. We are usually the only one

	 * holding a reference to newpage at this point. We used to have a BUG

	 * here if trylock_page(newpage) fails, but would like to allow for

	 * cases where there might be a race with the previous use of newpage.

	 * This is much like races on refcount of oldpage: just don't BUG().

	 */

	if (unlikely(!trylock_page(newpage)))

		goto out_unlock;



	if (unlikely(isolated_balloon_page(page))) {

		/*

		 * A ballooned page does not need any special attention from
@@ -870,7 +873,7 @@ static int __unmap_and_move(struct page *page, struct page *newpage, 
		 * the page migration right away (proteced by page lock).

		 */

		rc = balloon_page_migrate(newpage, page, mode);

		goto out_unlock;

		goto out_unlock_both;

	}



	/*
@@ -889,30 +892,27 @@ static int __unmap_and_move(struct page *page, struct page *newpage, 
		VM_BUG_ON_PAGE(PageAnon(page), page);

		if (page_has_private(page)) {

			try_to_free_buffers(page);

			goto out_unlock;

		}

		goto skip_unmap;

			goto out_unlock_both;

		}



	/* Establish migration ptes or remove ptes */

	if (page_mapped(page)) {

	} else if (page_mapped(page)) {

		/* Establish migration ptes */

		try_to_unmap(page,

			TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);

		page_was_mapped = 1;

	}



skip_unmap:

	if (!page_mapped(page))

		rc = move_to_new_page(newpage, page, page_was_mapped, mode);



	if (rc && page_was_mapped)

		remove_migration_ptes(page, page);



out_unlock_both:

	unlock_page(newpage);

out_unlock:

	/* Drop an anon_vma reference if we took one */

	if (anon_vma)

		put_anon_vma(anon_vma);



out_unlock:

	unlock_page(page);

out:

	return rc;
@@ -1056,6 +1056,9 @@ static int unmap_and_move_huge_page(new_page_t get_new_page, 
	if (PageAnon(hpage))

		anon_vma = page_get_anon_vma(hpage);



	if (unlikely(!trylock_page(new_hpage)))

		goto put_anon;



	if (page_mapped(hpage)) {

		try_to_unmap(hpage,

			TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
@@ -1068,6 +1071,9 @@ static int unmap_and_move_huge_page(new_page_t get_new_page, 
	if (rc != MIGRATEPAGE_SUCCESS && page_was_mapped)

		remove_migration_ptes(hpage, hpage);



	unlock_page(new_hpage);



put_anon:

	if (anon_vma)

		put_anon_vma(anon_vma);