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Subject[PATCH 3/7] Introduce isolate_lru_page_nolock() as a lockless version of isolate_lru_page()
Date

Migration uses isolate_lru_page() to isolate an LRU page. This acquires
the zone->lru_lock to safely remove the page and place it on a private
list. However, this prevents the caller from batching up isolation of
multiple pages. This patch introduces a nolock version of isolate_lru_page()
for callers that are aware of the locking requirements.

Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Acked-by: Andy Whitcroft <apw@shadowen.org>
---
include/linux/migrate.h | 8 +++++++-
mm/migrate.c | 36 +++++++++++++++++++++++++++---------
2 files changed, 34 insertions(+), 10 deletions(-)
diff -rup -X /usr/src/patchset-0.6/bin//dontdiff linux-2.6.22-rc4-mm2-015_migration_flatmem/include/linux/migrate.h linux-2.6.22-rc4-mm2-020_isolate_nolock/include/linux/migrate.h
--- linux-2.6.22-rc4-mm2-015_migration_flatmem/include/linux/migrate.h 2007-06-15 16:25:37.000000000 +0100
+++ linux-2.6.22-rc4-mm2-020_isolate_nolock/include/linux/migrate.h 2007-06-15 16:25:46.000000000 +0100
@@ -27,6 +27,8 @@ static inline int vma_migratable(struct
#endif

#ifdef CONFIG_MIGRATION
+extern int locked_isolate_lru_page(struct zone *zone, struct page *p,
+ struct list_head *pagelist);
extern int isolate_lru_page(struct page *p, struct list_head *pagelist);
extern int putback_lru_pages(struct list_head *l);
extern int migrate_page(struct address_space *,
@@ -41,7 +43,11 @@ extern int migrate_vmas(struct mm_struct
const nodemask_t *from, const nodemask_t *to,
unsigned long flags);
#else
-
+static inline int locked_isolate_lru_page(struct zone *zone, struct page *p,
+ struct list_head *list)
+{
+ return -ENOSYS;
+}
static inline int isolate_lru_page(struct page *p, struct list_head *list)
{ return -ENOSYS; }
static inline int putback_lru_pages(struct list_head *l) { return 0; }
diff -rup -X /usr/src/patchset-0.6/bin//dontdiff linux-2.6.22-rc4-mm2-015_migration_flatmem/mm/migrate.c linux-2.6.22-rc4-mm2-020_isolate_nolock/mm/migrate.c
--- linux-2.6.22-rc4-mm2-015_migration_flatmem/mm/migrate.c 2007-06-15 16:25:31.000000000 +0100
+++ linux-2.6.22-rc4-mm2-020_isolate_nolock/mm/migrate.c 2007-06-15 16:25:46.000000000 +0100
@@ -41,6 +41,32 @@
* -EBUSY: page not on LRU list
* 0: page removed from LRU list and added to the specified list.
*/
+int locked_isolate_lru_page(struct zone *zone, struct page *page,
+ struct list_head *pagelist)
+{
+ int ret = -EBUSY;
+
+ if (PageLRU(page) && get_page_unless_zero(page)) {
+ ret = 0;
+ ClearPageLRU(page);
+ if (PageActive(page))
+ del_page_from_active_list(zone, page);
+ else
+ del_page_from_inactive_list(zone, page);
+ list_add_tail(&page->lru, pagelist);
+ }
+
+ return ret;
+}
+
+/*
+ * Acquire the zone->lru_lock and isolate one page from the LRU lists. If
+ * successful put it onto the indicated list with elevated page count.
+ *
+ * Result:
+ * -EBUSY: page not on LRU list
+ * 0: page removed from LRU list and added to the specified list.
+ */
int isolate_lru_page(struct page *page, struct list_head *pagelist)
{
int ret = -EBUSY;
@@ -49,15 +75,7 @@ int isolate_lru_page(struct page *page,
struct zone *zone = page_zone(page);

spin_lock_irq(&zone->lru_lock);
- if (PageLRU(page) && get_page_unless_zero(page)) {
- ret = 0;
- ClearPageLRU(page);
- if (PageActive(page))
- del_page_from_active_list(zone, page);
- else
- del_page_from_inactive_list(zone, page);
- list_add_tail(&page->lru, pagelist);
- }
+ ret = locked_isolate_lru_page(zone, page, pagelist);
spin_unlock_irq(&zone->lru_lock);
}
return ret;
-
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