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

Christoph Lameter
2006-11-30T23:41:48Z

I think you initial suggestion of adding a counter to the anon_vma may
work. Here is a patch that may allow us to keep the anon_vma around
without holding mmap_sem. Seems to be simple.

Hugh?

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 17:39:48.429639786 -0600
@@ -218,6 +218,7 @@ static void remove_anon_migration_ptes(s
struct anon_vma *anon_vma;
struct vm_area_struct *vma;
unsigned long mapping;
+ int empty;

mapping = (unsigned long)new->mapping;

@@ -229,11 +230,15 @@ static void remove_anon_migration_ptes(s
*/
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);
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 17:39:17.795109159 -0600
@@ -151,7 +151,7 @@ void anon_vma_unlink(struct vm_area_stru
list_del(&vma->anon_vma_node);

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

if (empty)
@@ -787,6 +787,9 @@ static int try_to_unmap_anon(struct page
if (!anon_vma)
return ret;

+ if (migration)
+ 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))