This is a patch from KAMEZAWA Hiroyuki for using page migration on remote
processes without races. This patch is still undergoing development and
is expected to be a pre-requisite for both memory hot-remove and memory
compaction.
Changelog from KAMEZAWA Hiroyuki version
o Removed the MIGRATION_BY_KERNEL as a compile-time option
=====
This patch adds a feature that the kernel can migrate user pages by its own
context.
Now, sys_migrate(), a system call to migrate pages, works well.
When we want to migrate pages by some kernel codes, we have 2 approachs.
(a) acquire some mm->sem of a mapper of the target page.
(b) avoid race condition by additional check codes.
This patch implements (b) and adds following 2 codes.
1. delay freeing anon_vma while a page which belongs to it is migrated.
2. check page_mapped() before calling try_to_unmap().
Maybe more check will be needed. At least, this patch's migration_nocntext()
works well under heavy memory pressure on my environment.
From: KAMEZAWA Hiroyuki <[email protected]>
Signed-off-by: Yasonori Goto <[email protected]>
Signed-off-by: KAMEZAWA Hiroyuki <[email protected]>
Signed-off-by: Mel Gorman <[email protected]>
---
include/linux/migrate.h | 3 ++-
include/linux/rmap.h | 24 ++++++++++++++++++++++++
mm/migrate.c | 42 +++++++++++++++++++++++++++++++++---------
mm/rmap.c | 23 +++++++++++++++++++++++
4 files changed, 82 insertions(+), 10 deletions(-)
diff -rup -X /usr/src/patchset-0.6/bin//dontdiff linux-2.6.22-rc2-mm1-001_lameter-v4r4/include/linux/migrate.h linux-2.6.22-rc2-mm1-005_migrate_nocontext/include/linux/migrate.h
--- linux-2.6.22-rc2-mm1-001_lameter-v4r4/include/linux/migrate.h 2007-05-19 05:06:17.000000000 +0100
+++ linux-2.6.22-rc2-mm1-005_migrate_nocontext/include/linux/migrate.h 2007-05-28 14:11:32.000000000 +0100
@@ -30,7 +30,8 @@ extern int putback_lru_pages(struct list
extern int migrate_page(struct address_space *,
struct page *, struct page *);
extern int migrate_pages(struct list_head *l, new_page_t x, unsigned long);
-
+extern int migrate_pages_nocontext(struct list_head *l, new_page_t x,
+ unsigned long);
extern int fail_migrate_page(struct address_space *,
struct page *, struct page *);
diff -rup -X /usr/src/patchset-0.6/bin//dontdiff linux-2.6.22-rc2-mm1-001_lameter-v4r4/include/linux/rmap.h linux-2.6.22-rc2-mm1-005_migrate_nocontext/include/linux/rmap.h
--- linux-2.6.22-rc2-mm1-001_lameter-v4r4/include/linux/rmap.h 2007-05-19 05:06:17.000000000 +0100
+++ linux-2.6.22-rc2-mm1-005_migrate_nocontext/include/linux/rmap.h 2007-05-28 14:11:32.000000000 +0100
@@ -26,12 +26,16 @@
struct anon_vma {
spinlock_t lock; /* Serialize access to vma list */
struct list_head head; /* List of private "related" vmas */
+#ifdef CONFIG_MIGRATION
+ atomic_t ref; /* special refcnt for migration */
+#endif
};
#ifdef CONFIG_MMU
extern struct kmem_cache *anon_vma_cachep;
+#ifndef CONFIG_MIGRATION
static inline struct anon_vma *anon_vma_alloc(void)
{
return kmem_cache_alloc(anon_vma_cachep, GFP_KERNEL);
@@ -41,6 +45,26 @@ static inline void anon_vma_free(struct
{
kmem_cache_free(anon_vma_cachep, anon_vma);
}
+#define anon_vma_hold(page) do{}while(0)
+#define anon_vma_release(anon) do{}while(0)
+
+#else /* CONFIG_MIGRATION */
+static inline struct anon_vma *anon_vma_alloc(void)
+{
+ struct anon_vma *ret = kmem_cache_alloc(anon_vma_cachep, GFP_KERNEL);
+ if (ret)
+ atomic_set(&ret->ref, 0);
+ return ret;
+}
+static inline void anon_vma_free(struct anon_vma *anon_vma)
+{
+ if (atomic_read(&anon_vma->ref) == 0)
+ kmem_cache_free(anon_vma_cachep, anon_vma);
+}
+extern struct anon_vma *anon_vma_hold(struct page *page);
+extern void anon_vma_release(struct anon_vma *anon_vma);
+
+#endif /* CONFIG_MIGRATION */
static inline void anon_vma_lock(struct vm_area_struct *vma)
{
diff -rup -X /usr/src/patchset-0.6/bin//dontdiff linux-2.6.22-rc2-mm1-001_lameter-v4r4/mm/migrate.c linux-2.6.22-rc2-mm1-005_migrate_nocontext/mm/migrate.c
--- linux-2.6.22-rc2-mm1-001_lameter-v4r4/mm/migrate.c 2007-05-24 10:13:34.000000000 +0100
+++ linux-2.6.22-rc2-mm1-005_migrate_nocontext/mm/migrate.c 2007-05-28 14:11:32.000000000 +0100
@@ -607,11 +607,12 @@ static int move_to_new_page(struct page
* to the newly allocated page in newpage.
*/
static int unmap_and_move(new_page_t get_new_page, unsigned long private,
- struct page *page, int force)
+ struct page *page, int force, int context)
{
int rc = 0;
int *result = NULL;
struct page *newpage = get_new_page(page, private, &result);
+ struct anon_vma *anon_vma = NULL;
if (!newpage)
return -ENOMEM;
@@ -633,15 +634,22 @@ static int unmap_and_move(new_page_t get
wait_on_page_writeback(page);
}
- /*
- * Establish migration ptes or remove ptes
- */
- try_to_unmap(page, 1);
+ if (PageAnon(page) && context)
+ /* hold this anon_vma until page migration ends */
+ anon_vma = anon_vma_hold(page);
+
+ if (page_mapped(page))
+ try_to_unmap(page, 1);
+
if (!page_mapped(page))
rc = move_to_new_page(newpage, page);
- if (rc)
+ if (rc) {
remove_migration_ptes(page, page);
+ }
+
+ if (anon_vma)
+ anon_vma_release(anon_vma);
unlock:
unlock_page(page);
@@ -686,8 +694,8 @@ move_newpage:
*
* Return: Number of pages not migrated or error code.
*/
-int migrate_pages(struct list_head *from,
- new_page_t get_new_page, unsigned long private)
+int __migrate_pages(struct list_head *from,
+ new_page_t get_new_page, unsigned long private, int context)
{
int retry = 1;
int nr_failed = 0;
@@ -707,7 +715,7 @@ int migrate_pages(struct list_head *from
cond_resched();
rc = unmap_and_move(get_new_page, private,
- page, pass > 2);
+ page, pass > 2, context);
switch(rc) {
case -ENOMEM:
@@ -737,6 +745,22 @@ out:
return nr_failed + retry;
}
+int migrate_pages(struct list_head *from,
+ new_page_t get_new_page, unsigned long private)
+{
+ return __migrate_pages(from, get_new_page, private, 0);
+}
+
+/*
+ * When page migration is issued by the kernel itself without page mapper's
+ * mm->sem, we have to be more careful to do page migration.
+ */
+int migrate_pages_nocontext(struct list_head *from,
+ new_page_t get_new_page, unsigned long private)
+{
+ return __migrate_pages(from, get_new_page, private, 1);
+}
+
#ifdef CONFIG_NUMA
/*
* Move a list of individual pages
diff -rup -X /usr/src/patchset-0.6/bin//dontdiff linux-2.6.22-rc2-mm1-001_lameter-v4r4/mm/rmap.c linux-2.6.22-rc2-mm1-005_migrate_nocontext/mm/rmap.c
--- linux-2.6.22-rc2-mm1-001_lameter-v4r4/mm/rmap.c 2007-05-24 10:13:34.000000000 +0100
+++ linux-2.6.22-rc2-mm1-005_migrate_nocontext/mm/rmap.c 2007-05-28 14:11:32.000000000 +0100
@@ -204,6 +204,29 @@ static void page_unlock_anon_vma(struct
rcu_read_unlock();
}
+#ifdef CONFIG_MIGRATION
+struct anon_vma *anon_vma_hold(struct page *page) {
+ struct anon_vma *anon_vma;
+ anon_vma = page_lock_anon_vma(page);
+ if (!anon_vma)
+ return NULL;
+ atomic_set(&anon_vma->ref, 1);
+ spin_unlock(&anon_vma->lock);
+ return anon_vma;
+}
+
+void anon_vma_release(struct anon_vma *anon_vma)
+{
+ int empty;
+ spin_lock(&anon_vma->lock);
+ atomic_set(&anon_vma->ref, 0);
+ empty = list_empty(&anon_vma->head);
+ spin_unlock(&anon_vma->lock);
+ if (empty)
+ anon_vma_free(anon_vma);
+}
+#endif /* CONFIG_MIGRATION */
+
/*
* At what user virtual address is page expected in vma?
*/
-
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