Re: [RFC][PATCH 0/1] Node-based reclaim/migration

Christoph Lameter
2006-12-01T02:44:30Z

Fixed up patch with more comments and a check that the migration_count is
zero before freeing.

Index: linux-2.6.19-rc6-mm2/include/linux/rmap.h
===================================================================
--- linux-2.6.19-rc6-mm2.orig/include/linux/rmap.h 2006-11-15 22:03:40.000000000 -0600
+++ linux-2.6.19-rc6-mm2/include/linux/rmap.h 2006-11-30 17:39:17.643728656 -0600
@@ -26,6 +26,7 @@
struct anon_vma {
spinlock_t lock; /* Serialize access to vma list */
struct list_head head; /* List of private "related" vmas */
+ int migration_count; /* # processes migrating pages */
};

#ifdef CONFIG_MMU
Index: linux-2.6.19-rc6-mm2/mm/migrate.c
===================================================================
--- linux-2.6.19-rc6-mm2.orig/mm/migrate.c 2006-11-29 18:37:17.797934398 -0600
+++ linux-2.6.19-rc6-mm2/mm/migrate.c 2006-11-30 20:41:13.810836561 -0600
@@ -209,15 +209,12 @@ static void remove_file_migration_ptes(s
spin_unlock(&mapping->i_mmap_lock);
}

-/*
- * Must hold mmap_sem lock on at least one of the vmas containing
- * the page so that the anon_vma cannot vanish.
- */
static void remove_anon_migration_ptes(struct page *old, struct page *new)
{
struct anon_vma *anon_vma;
struct vm_area_struct *vma;
unsigned long mapping;
+ int empty;

mapping = (unsigned long)new->mapping;

@@ -225,15 +222,20 @@ static void remove_anon_migration_ptes(s
return;

/*
- * We hold the mmap_sem lock. So no need to call page_lock_anon_vma.
+ * We have increased migration_count So no need to call
+ * page_lock_anon_vma.
*/
anon_vma = (struct anon_vma *) (mapping - PAGE_MAPPING_ANON);
spin_lock(&anon_vma->lock);
+ anon_vma->migration_count--;

list_for_each_entry(vma, &anon_vma->head, anon_vma_node)
remove_migration_pte(vma, old, new);

+ empty = list_empty(&anon_vma->head) && !anon_vma->migration_count;
spin_unlock(&anon_vma->lock);
+ if (empty)
+ anon_vma_free(anon_vma);
}

/*
Index: linux-2.6.19-rc6-mm2/mm/rmap.c
===================================================================
--- linux-2.6.19-rc6-mm2.orig/mm/rmap.c 2006-11-15 22:03:40.000000000 -0600
+++ linux-2.6.19-rc6-mm2/mm/rmap.c 2006-11-30 20:39:52.266554217 -0600
@@ -150,8 +150,8 @@ void anon_vma_unlink(struct vm_area_stru
validate_anon_vma(vma);
list_del(&vma->anon_vma_node);

- /* We must garbage collect the anon_vma if it's empty */
- empty = list_empty(&anon_vma->head);
+ /* We must garbage collect the anon_vma if it's unused */
+ empty = list_empty(&anon_vma->head) && !anon_vma->migration_count;
spin_unlock(&anon_vma->lock);

if (empty)
@@ -787,6 +787,10 @@ static int try_to_unmap_anon(struct page
if (!anon_vma)
return ret;

+ if (migration)
+ /* Prevent freeing while migrating pages */
+ anon_vma->migration_count++;
+
list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {
ret = try_to_unmap_one(page, vma, migration);
if (ret == SWAP_FAIL || !page_mapped(page))