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SubjectRe: [RFC] memory hotremove patch take 2 [07/10] (delay freeing anon_vma)
Delaying freeing anon_vma until migration finishes.

We cannot trust page->mapping (of ANON) when page_mapcount(page) ==0.

page migration puts page_mocount(page) to be 0. So we have to
guarantee anon_vma pointed by page->mapping is valid by some hook.

Usual page migration guarantees this by mm->sem. but we can't do it.
So, just delaying freeing anon_vma.

Signed-Off-By: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Yasunori Goto <y-goto@jp.fujitsu.com>

include/linux/migrate.h | 2 ++
include/linux/page_isolation.h | 14 ++++++++++++++
include/linux/rmap.h | 22 ++++++++++++++++++++++
mm/Kconfig | 12 ++++++++++++
mm/memory_hotplug.c | 4 ++--
mm/migrate.c | 37 +++++++++++++++++++++++++++++++------
mm/rmap.c | 36 +++++++++++++++++++++++++++++++++++-
7 files changed, 118 insertions(+), 9 deletions(-)

Index: current_test/mm/migrate.c
===================================================================
--- current_test.orig/mm/migrate.c 2007-05-08 15:06:50.000000000 +0900
+++ current_test/mm/migrate.c 2007-05-08 15:08:24.000000000 +0900
@@ -28,6 +28,7 @@
#include <linux/mempolicy.h>
#include <linux/vmalloc.h>
#include <linux/security.h>
+#include <linux/page_isolation.h>

#include "internal.h"

@@ -607,7 +608,7 @@ 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 flag)
{
int rc = 0;
int *result = NULL;
@@ -632,7 +633,10 @@ static int unmap_and_move(new_page_t get
goto unlock;
wait_on_page_writeback(page);
}
-
+ if (PageAnon(page) && is_migrate_nocontext(flag)) {
+ /* hold this anon_vma until remove_migration_ptes() finishes */
+ anon_vma_hold(page);
+ }
/*
* Establish migration ptes or remove ptes
*/
@@ -640,8 +644,14 @@ static int unmap_and_move(new_page_t get
if (!page_mapped(page))
rc = move_to_new_page(newpage, page);

- if (rc)
+ if (rc) {
remove_migration_ptes(page, page);
+ if (PageAnon(page) && is_migrate_nocontext(flag))
+ anon_vma_release(page);
+ } else {
+ if (PageAnon(newpage) && is_migrate_nocontext(flag))
+ anon_vma_release(page);
+ }

unlock:
unlock_page(page);
@@ -686,8 +696,8 @@ 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)
+static int __migrate_pages(struct list_head *from,
+ new_page_t get_new_page, unsigned long private, int flag)
{
int retry = 1;
int nr_failed = 0;
@@ -707,7 +717,7 @@ int migrate_pages(struct list_head *from
cond_resched();

rc = unmap_and_move(get_new_page, private,
- page, pass > 2);
+ page, pass > 2, flag);

switch(rc) {
case -ENOMEM:
@@ -737,6 +747,21 @@ 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);
+}
+
+#ifdef CONFIG_MIGRATION_REMOVE
+int migrate_pages_and_remove(struct list_head *from,
+ new_page_t get_new_page, unsigned long private)
+{
+ return __migrate_pages(from, get_new_page, private,
+ MIGRATE_NOCONTEXT);
+}
+#endif
+
#ifdef CONFIG_NUMA
/*
* Move a list of individual pages
Index: current_test/include/linux/rmap.h
===================================================================
--- current_test.orig/include/linux/rmap.h 2007-05-08 15:06:49.000000000 +0900
+++ current_test/include/linux/rmap.h 2007-05-08 15:08:07.000000000 +0900
@@ -26,6 +26,9 @@
struct anon_vma {
spinlock_t lock; /* Serialize access to vma list */
struct list_head head; /* List of private "related" vmas */
+#ifdef CONFIG_MIGRATION_REMOVE
+ atomic_t hold; /* == 0 if we can free this immediately */
+#endif
};

#ifdef CONFIG_MMU
@@ -37,10 +40,14 @@ static inline struct anon_vma *anon_vma_
return kmem_cache_alloc(anon_vma_cachep, GFP_KERNEL);
}

+#ifndef CONFIG_MIGRATION_REMOVE
static inline void anon_vma_free(struct anon_vma *anon_vma)
{
kmem_cache_free(anon_vma_cachep, anon_vma);
}
+#else
+extern void anon_vma_free(struct anon_vma *anon_vma);
+#endif

static inline void anon_vma_lock(struct vm_area_struct *vma)
{
@@ -75,6 +82,21 @@ void page_add_file_rmap(struct page *);
void page_dup_rmap(struct page *page, struct vm_area_struct *vma, unsigned long address);
void page_remove_rmap(struct page *, struct vm_area_struct *);

+#ifdef CONFIG_MIGRATION_REMOVE
+/*
+ * While Page migration without any process context, we doesn't have
+ * mm->sem. Because page->mapcount goes down to 0 while migration,
+ * we cannot trust page->mapping value.
+ * These two functions prevents anon_vma from being freed while
+ * migration.
+ */
+void anon_vma_hold(struct page *page);
+void anon_vma_release(struct page *page);
+#else /* !CONFIG_MIGRATION_REMOVE */
+#define anon_vma_hold(page) do{}while(0)
+#define anon_vma_release(page) do{}while(0)
+#endif /* CONFIG_MIGRATION_REMOVE */
+
/*
* Called from mm/vmscan.c to handle paging out
*/
Index: current_test/mm/rmap.c
===================================================================
--- current_test.orig/mm/rmap.c 2007-05-08 15:06:50.000000000 +0900
+++ current_test/mm/rmap.c 2007-05-08 15:08:07.000000000 +0900
@@ -155,8 +155,9 @@ void anon_vma_unlink(struct vm_area_stru
empty = list_empty(&anon_vma->head);
spin_unlock(&anon_vma->lock);

- if (empty)
+ if (empty) {
anon_vma_free(anon_vma);
+ }
}

static void anon_vma_ctor(void *data, struct kmem_cache *cachep,
@@ -1003,3 +1004,36 @@ int try_to_unmap(struct page *page, int
return ret;
}

+#ifdef CONFIG_MIGRATION_REMOVE
+
+void anon_vma_free(struct anon_vma *anon)
+{
+ if (atomic_read(&anon->hold) == 0) {
+ kmem_cache_free(anon_vma_cachep, anon);
+ }
+}
+
+void anon_vma_hold(struct page *page)
+{
+ struct anon_vma *anon_vma;
+ anon_vma = page_lock_anon_vma(page);
+ if (!anon_vma)
+ return;
+ atomic_set(&anon_vma->hold, 1);
+ spin_unlock(&anon_vma->lock);
+}
+
+void anon_vma_release(struct page *page)
+{
+ struct anon_vma *anon_vma;
+ int empty;
+ anon_vma = page_lock_anon_vma(page);
+ if (!anon_vma)
+ return;
+ atomic_set(&anon_vma->hold, 0);
+ empty = list_empty(&anon_vma->head);
+ spin_unlock(&anon_vma->lock);
+ if (empty)
+ anon_vma_free(anon_vma);
+}
+#endif
Index: current_test/mm/Kconfig
===================================================================
--- current_test.orig/mm/Kconfig 2007-05-08 15:08:06.000000000 +0900
+++ current_test/mm/Kconfig 2007-05-08 15:08:24.000000000 +0900
@@ -131,6 +131,7 @@ config MEMORY_HOTREMOVE
depends on MEMORY_HOTPLUG_SPARSE
select MIGRATION
select PAGE_ISOLATION
+ select MIGRATION_REMOVE

# Heavily threaded applications may benefit from splitting the mm-wide
# page_table_lock, so that faults on different parts of the user address
@@ -158,6 +159,17 @@ config MIGRATION
example on NUMA systems to put pages nearer to the processors accessing
the page.

+config MIGRATION_REMOVE
+ bool "Page migration for memory remove"
+ def_bool y
+ depends on MEMORY_HOTREMOVE
+ help
+ When Memory-Hotremove is executed, page migraion runs.
+ But a process which does page migraion doesn't have context of
+ migration target pages. This has a small race condition.
+ If this config is selected, some workaround for fix them is enabled.
+ This may be add slight performance influence.
+
config RESOURCES_64BIT
bool "64 bit Memory and IO resources (EXPERIMENTAL)" if (!64BIT && EXPERIMENTAL)
default 64BIT
Index: current_test/include/linux/migrate.h
===================================================================
--- current_test.orig/include/linux/migrate.h 2007-05-08 15:06:49.000000000 +0900
+++ current_test/include/linux/migrate.h 2007-05-08 15:08:07.000000000 +0900
@@ -30,6 +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_and_remove(struct list_head *l,
+ new_page_t x, unsigned long);

extern int fail_migrate_page(struct address_space *,
struct page *, struct page *);
Index: current_test/mm/memory_hotplug.c
===================================================================
--- current_test.orig/mm/memory_hotplug.c 2007-05-08 15:08:06.000000000 +0900
+++ current_test/mm/memory_hotplug.c 2007-05-08 15:08:07.000000000 +0900
@@ -345,7 +345,7 @@ static int do_migrate_and_isolate_pages(
if (!pfn_valid(pfn)) /* never happens in sparsemem */
continue;
page = pfn_to_page(pfn);
- if (is_page_isolated(info,page))
+ if (PageReserved(page))
continue;
ret = isolate_lru_page(page, &source);

@@ -367,7 +367,7 @@ static int do_migrate_and_isolate_pages(
if (list_empty(&source))
goto out;
/* this function returns # of failed pages */
- ret = migrate_pages(&source, hotremove_migrate_alloc,
+ ret = migrate_pages_and_remove(&source, hotremove_migrate_alloc,
(unsigned long)info);
out:
return ret;
Index: current_test/include/linux/page_isolation.h
===================================================================
--- current_test.orig/include/linux/page_isolation.h 2007-05-08 15:08:05.000000000 +0900
+++ current_test/include/linux/page_isolation.h 2007-05-08 15:08:24.000000000 +0900
@@ -32,6 +32,13 @@ is_page_isolated(struct isolation_info *
return 0;
}

+#define MIGRATE_NOCONTEXT 0x1
+static inline int
+is_migrate_nocontext(int flag)
+{
+ return (flag & MIGRATE_NOCONTEXT) == MIGRATE_NOCONTEXT;
+}
+
extern struct isolation_info *
register_isolation(unsigned long start, unsigned long end);

@@ -50,5 +57,12 @@ page_under_isolation(struct zone *zone,
return 0;
}

+
+static inline int
+is_migrate_nocontext(int flag)
+{
+ return 0;
+}
+
#endif
#endif
--
Yasunori Goto


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