Commit c3fcf8a5 authored by Christoph Lameter's avatar Christoph Lameter Committed by Linus Torvalds
Browse files

[PATCH] page migration cleanup: extract try_to_unmap from migration functions 



Extract try_to_unmap and rename remove_references -> move_mapping

try_to_unmap() may significantly change the page state by for example setting
the dirty bit.  It is therefore best to unmap in migrate_pages() before
calling any migration functions.

migrate_page_remove_references() will then only move the new page in place of
the old page in the mapping.  Rename the function to
migrate_page_move_mapping().

This allows us to get rid of the special unmapping for the fallback path.

Signed-off-by: default avatarChristoph Lameter <clameter@sgi.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 5b5c7120

mm/migrate.c

+31 −45
Original line number Diff line number Diff line
@@ -166,15 +166,14 @@ retry: 
}



/*

 * Remove references for a page and establish the new page with the correct

 * basic settings to be able to stop accesses to the page.

 * Replace the page in the mapping.

 *

 * The number of remaining references must be:

 * 1 for anonymous pages without a mapping

 * 2 for pages with a mapping

 * 3 for pages with a mapping and PagePrivate set.

 */

static int migrate_page_remove_references(struct page *newpage,

static int migrate_page_move_mapping(struct page *newpage,

				struct page *page)

{

	struct address_space *mapping = page_mapping(page);
@@ -183,35 +182,6 @@ static int migrate_page_remove_references(struct page *newpage, 
	if (!mapping)

		return -EAGAIN;



	/*

	 * Establish swap ptes for anonymous pages or destroy pte

	 * maps for files.

	 *

	 * In order to reestablish file backed mappings the fault handlers

	 * will take the radix tree_lock which may then be used to stop

  	 * processses from accessing this page until the new page is ready.

	 *

	 * A process accessing via a swap pte (an anonymous page) will take a

	 * page_lock on the old page which will block the process until the

	 * migration attempt is complete. At that time the PageSwapCache bit

	 * will be examined. If the page was migrated then the PageSwapCache

	 * bit will be clear and the operation to retrieve the page will be

	 * retried which will find the new page in the radix tree. Then a new

	 * direct mapping may be generated based on the radix tree contents.

	 *

	 * If the page was not migrated then the PageSwapCache bit

	 * is still set and the operation may continue.

	 */

	if (try_to_unmap(page, 1) == SWAP_FAIL)

		/* A vma has VM_LOCKED set -> permanent failure */

		return -EPERM;



	/*

	 * Give up if we were unable to remove all mappings.

	 */

	if (page_mapcount(page))

		return -EAGAIN;



	write_lock_irq(&mapping->tree_lock);



	radix_pointer = (struct page **)radix_tree_lookup_slot(
@@ -310,7 +280,7 @@ int migrate_page(struct page *newpage, struct page *page) 


	BUG_ON(PageWriteback(page));	/* Writeback must be complete */



	rc = migrate_page_remove_references(newpage, page);

	rc = migrate_page_move_mapping(newpage, page);



	if (rc)

		return rc;
@@ -349,7 +319,7 @@ int buffer_migrate_page(struct page *newpage, struct page *page) 


	head = page_buffers(page);



	rc = migrate_page_remove_references(newpage, page);

	rc = migrate_page_move_mapping(newpage, page);



	if (rc)

		return rc;
@@ -481,6 +451,33 @@ redo: 
		newpage = lru_to_page(to);

		lock_page(newpage);



		/*

		 * Establish swap ptes for anonymous pages or destroy pte

		 * maps for files.

		 *

		 * In order to reestablish file backed mappings the fault handlers

		 * will take the radix tree_lock which may then be used to stop

	  	 * processses from accessing this page until the new page is ready.

		 *

		 * A process accessing via a swap pte (an anonymous page) will take a

		 * page_lock on the old page which will block the process until the

		 * migration attempt is complete. At that time the PageSwapCache bit

		 * will be examined. If the page was migrated then the PageSwapCache

		 * bit will be clear and the operation to retrieve the page will be

		 * retried which will find the new page in the radix tree. Then a new

		 * direct mapping may be generated based on the radix tree contents.

		 *

		 * If the page was not migrated then the PageSwapCache bit

		 * is still set and the operation may continue.

		 */

		rc = -EPERM;

		if (try_to_unmap(page, 1) == SWAP_FAIL)

			/* A vma has VM_LOCKED set -> permanent failure */

			goto unlock_both;



		rc = -EAGAIN;

		if (page_mapped(page))

			goto unlock_both;

		/*

		 * Pages are properly locked and writeback is complete.

		 * Try to migrate the page.
@@ -501,17 +498,6 @@ redo: 
			goto unlock_both;

                }



		/* Make sure the dirty bit is up to date */

		if (try_to_unmap(page, 1) == SWAP_FAIL) {

			rc = -EPERM;

			goto unlock_both;

		}



		if (page_mapcount(page)) {

			rc = -EAGAIN;

			goto unlock_both;

		}



		/*

		 * Default handling if a filesystem does not provide

		 * a migration function. We can only migrate clean

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