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[PATCH] Swapless page migration: modify core logic

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Use the migration entries for page migration

This modifies the migration code to use the new migration entries.  It now
becomes possible to migrate anonymous pages without having to add a swap
entry.

We add a couple of new functions to replace migration entries with the proper
ptes.

We cannot take the tree_lock for migrating anonymous pages anymore.  However,
we know that we hold the only remaining reference to the page when the page
count reaches 1.

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 02:03:37 -07:00 committed by Linus Torvalds
parent d75a0fcda2
commit 6c5240ae7f
2 changed files with 23 additions and 34 deletions
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4
mm/Kconfig
View file

@ -138,8 +138,8 @@ config SPLIT_PTLOCK_CPUS
#
config MIGRATION
bool "Page migration"
def_bool y if NUMA
depends on SWAP && NUMA
def_bool y
depends on NUMA
help
Allows the migration of the physical location of pages of processes
while the virtual addresses are not changed. This is useful for

53
mm/migrate.c
View file

@ -254,14 +254,20 @@ static int migrate_page_move_mapping(struct address_space *mapping,
{
struct page **radix_pointer;
if (!mapping) {
/* Anonymous page */
if (page_count(page) != 1)
return -EAGAIN;
return 0;
}
write_lock_irq(&mapping->tree_lock);
radix_pointer = (struct page **)radix_tree_lookup_slot(
&mapping->page_tree,
page_index(page));
if (!page_mapping(page) ||
page_count(page) != 2 + !!PagePrivate(page) ||
if (page_count(page) != 2 + !!PagePrivate(page) ||
*radix_pointer != page) {
write_unlock_irq(&mapping->tree_lock);
return -EAGAIN;
@ -271,10 +277,12 @@ static int migrate_page_move_mapping(struct address_space *mapping,
* Now we know that no one else is looking at the page.
*/
get_page(newpage);
#ifdef CONFIG_SWAP
if (PageSwapCache(page)) {
SetPageSwapCache(newpage);
set_page_private(newpage, page_private(page));
}
#endif
*radix_pointer = newpage;
__put_page(page);
@ -308,7 +316,9 @@ static void migrate_page_copy(struct page *newpage, struct page *page)
set_page_dirty(newpage);
}
#ifdef CONFIG_SWAP
ClearPageSwapCache(page);
#endif
ClearPageActive(page);
ClearPagePrivate(page);
set_page_private(page, 0);
@ -353,16 +363,6 @@ int migrate_page(struct address_space *mapping,
return rc;
migrate_page_copy(newpage, page);
/*
* Remove auxiliary swap entries and replace
* them with real ptes.
*
* Note that a real pte entry will allow processes that are not
* waiting on the page lock to use the new page via the page tables
* before the new page is unlocked.
*/
remove_from_swap(newpage);
return 0;
}
EXPORT_SYMBOL(migrate_page);
@ -530,23 +530,7 @@ int migrate_pages(struct list_head *from, struct list_head *to,
goto unlock_page;
/*
* 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.
* Establish migration ptes or remove ptes
*/
rc = -EPERM;
if (try_to_unmap(page, 1) == SWAP_FAIL)
@ -569,9 +553,9 @@ int migrate_pages(struct list_head *from, struct list_head *to,
*/
mapping = page_mapping(page);
if (!mapping)
goto unlock_both;
rc = migrate_page(mapping, newpage, page);
if (mapping->a_ops->migratepage)
else if (mapping->a_ops->migratepage)
/*
* Most pages have a mapping and most filesystems
* should provide a migration function. Anonymous
@ -584,10 +568,15 @@ int migrate_pages(struct list_head *from, struct list_head *to,
else
rc = fallback_migrate_page(mapping, newpage, page);
unlock_both:
if (!rc)
remove_migration_ptes(page, newpage);
unlock_page(newpage);
unlock_page:
if (rc)
remove_migration_ptes(page, page);
unlock_page(page);
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