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[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: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Christoph Lameter 2006-06-23 02:03:32 -07:00 committed by Linus Torvalds
parent 5b5c7120e2
commit c3fcf8a5da
1 changed files with 31 additions and 45 deletions
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76
mm/migrate.c
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@ -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