[PATCH v4 03/12] mm: balloon: use general non-lru movable page feature

From: Minchan Kim
Date: Wed Apr 27 2016 - 03:49:59 EST

Now, VM has a feature to migrate non-lru movable pages so
balloon doesn't need custom migration hooks in migrate.c
and compaction.c. Instead, this patch implements
page->mapping->a_ops->{isolate|migrate|putback} functions.

With that, we could remove hooks for ballooning in general
migration functions and make balloon compaction simple.

Cc: virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
Cc: Rafael Aquini <aquini@xxxxxxxxxx>
Cc: Konstantin Khlebnikov <koct9i@xxxxxxxxx>
Signed-off-by: Gioh Kim <gi-oh.kim@xxxxxxxxxxxxxxxx>
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
---
drivers/virtio/virtio_balloon.c | 52 +++++++++++++++++++--
include/linux/balloon_compaction.h | 51 ++++++---------------
include/uapi/linux/magic.h | 1 +
mm/balloon_compaction.c | 94 +++++++-------------------------------
mm/compaction.c | 7 ---
mm/migrate.c | 19 +-------
mm/vmscan.c | 2 +-
7 files changed, 83 insertions(+), 143 deletions(-)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 7b6d74f0c72f..04fc63b4a735 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -30,6 +30,7 @@
#include <linux/oom.h>
#include <linux/wait.h>
#include <linux/mm.h>
+#include <linux/mount.h>

/*
* Balloon device works in 4K page units. So each page is pointed to by
@@ -45,6 +46,10 @@ static int oom_pages = OOM_VBALLOON_DEFAULT_PAGES;
module_param(oom_pages, int, S_IRUSR | S_IWUSR);
MODULE_PARM_DESC(oom_pages, "pages to free on OOM");

+#ifdef CONFIG_BALLOON_COMPACTION
+static struct vfsmount *balloon_mnt;
+#endif
+
struct virtio_balloon {
struct virtio_device *vdev;
struct virtqueue *inflate_vq, *deflate_vq, *stats_vq;
@@ -486,6 +491,24 @@ static int virtballoon_migratepage(struct balloon_dev_info *vb_dev_info,

return MIGRATEPAGE_SUCCESS;
}
+
+static struct dentry *balloon_mount(struct file_system_type *fs_type,
+ int flags, const char *dev_name, void *data)
+{
+ static const struct dentry_operations ops = {
+ .d_dname = simple_dname,
+ };
+
+ return mount_pseudo(fs_type, "balloon-kvm:", NULL, &ops,
+ BALLOON_KVM_MAGIC);
+}
+
+static struct file_system_type balloon_fs = {
+ .name = "balloon-kvm",
+ .mount = balloon_mount,
+ .kill_sb = kill_anon_super,
+};
+
#endif /* CONFIG_BALLOON_COMPACTION */

static int virtballoon_probe(struct virtio_device *vdev)
@@ -515,9 +538,6 @@ static int virtballoon_probe(struct virtio_device *vdev)
vb->vdev = vdev;

balloon_devinfo_init(&vb->vb_dev_info);
-#ifdef CONFIG_BALLOON_COMPACTION
- vb->vb_dev_info.migratepage = virtballoon_migratepage;
-#endif

err = init_vqs(vb);
if (err)
@@ -527,13 +547,33 @@ static int virtballoon_probe(struct virtio_device *vdev)
vb->nb.priority = VIRTBALLOON_OOM_NOTIFY_PRIORITY;
err = register_oom_notifier(&vb->nb);
if (err < 0)
- goto out_oom_notify;
+ goto out_del_vqs;
+
+#ifdef CONFIG_BALLOON_COMPACTION
+ balloon_mnt = kern_mount(&balloon_fs);
+ if (IS_ERR(balloon_mnt)) {
+ err = PTR_ERR(balloon_mnt);
+ unregister_oom_notifier(&vb->nb);
+ goto out_del_vqs;
+ }
+
+ vb->vb_dev_info.migratepage = virtballoon_migratepage;
+ vb->vb_dev_info.inode = alloc_anon_inode(balloon_mnt->mnt_sb);
+ if (IS_ERR(vb->vb_dev_info.inode)) {
+ err = PTR_ERR(vb->vb_dev_info.inode);
+ kern_unmount(balloon_mnt);
+ unregister_oom_notifier(&vb->nb);
+ vb->vb_dev_info.inode = NULL;
+ goto out_del_vqs;
+ }
+ vb->vb_dev_info.inode->i_mapping->a_ops = &balloon_aops;
+#endif

virtio_device_ready(vdev);

return 0;

-out_oom_notify:
+out_del_vqs:
vdev->config->del_vqs(vdev);
out_free_vb:
kfree(vb);
@@ -567,6 +607,8 @@ static void virtballoon_remove(struct virtio_device *vdev)
cancel_work_sync(&vb->update_balloon_stats_work);

remove_common(vb);
+ if (vb->vb_dev_info.inode)
+ iput(vb->vb_dev_info.inode);
kfree(vb);
}

diff --git a/include/linux/balloon_compaction.h b/include/linux/balloon_compaction.h
index 9b0a15d06a4f..79542b2698ec 100644
--- a/include/linux/balloon_compaction.h
+++ b/include/linux/balloon_compaction.h
@@ -48,6 +48,7 @@
#include <linux/migrate.h>
#include <linux/gfp.h>
#include <linux/err.h>
+#include <linux/fs.h>

/*
* Balloon device information descriptor.
@@ -62,6 +63,7 @@ struct balloon_dev_info {
struct list_head pages; /* Pages enqueued & handled to Host */
int (*migratepage)(struct balloon_dev_info *, struct page *newpage,
struct page *page, enum migrate_mode mode);
+ struct inode *inode;
};

extern struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info);
@@ -73,45 +75,19 @@ static inline void balloon_devinfo_init(struct balloon_dev_info *balloon)
spin_lock_init(&balloon->pages_lock);
INIT_LIST_HEAD(&balloon->pages);
balloon->migratepage = NULL;
+ balloon->inode = NULL;
}

#ifdef CONFIG_BALLOON_COMPACTION
-extern bool balloon_page_isolate(struct page *page);
+extern const struct address_space_operations balloon_aops;
+extern bool balloon_page_isolate(struct page *page,
+ isolate_mode_t mode);
extern void balloon_page_putback(struct page *page);
-extern int balloon_page_migrate(struct page *newpage,
+extern int balloon_page_migrate(struct address_space *mapping,
+ struct page *newpage,
struct page *page, enum migrate_mode mode);

/*
- * __is_movable_balloon_page - helper to perform @page PageBalloon tests
- */
-static inline bool __is_movable_balloon_page(struct page *page)
-{
- return PageBalloon(page);
-}
-
-/*
- * balloon_page_movable - test PageBalloon to identify balloon pages
- * and PagePrivate to check that the page is not
- * isolated and can be moved by compaction/migration.
- *
- * As we might return false positives in the case of a balloon page being just
- * released under us, this need to be re-tested later, under the page lock.
- */
-static inline bool balloon_page_movable(struct page *page)
-{
- return PageBalloon(page) && PagePrivate(page);
-}
-
-/*
- * isolated_balloon_page - identify an isolated balloon page on private
- * compaction/migration page lists.
- */
-static inline bool isolated_balloon_page(struct page *page)
-{
- return PageBalloon(page);
-}
-
-/*
* balloon_page_insert - insert a page into the balloon's page list and make
* the page->private assignment accordingly.
* @balloon : pointer to balloon device
@@ -124,7 +100,7 @@ static inline void balloon_page_insert(struct balloon_dev_info *balloon,
struct page *page)
{
__SetPageBalloon(page);
- SetPagePrivate(page);
+ __SetPageMovable(page, balloon->inode->i_mapping);
set_page_private(page, (unsigned long)balloon);
list_add(&page->lru, &balloon->pages);
}
@@ -140,11 +116,14 @@ static inline void balloon_page_insert(struct balloon_dev_info *balloon,
static inline void balloon_page_delete(struct page *page)
{
__ClearPageBalloon(page);
+ __ClearPageMovable(page);
set_page_private(page, 0);
- if (PagePrivate(page)) {
- ClearPagePrivate(page);
+ /*
+ * No touch page.lru field once @page has been isolated
+ * because VM is using the field.
+ */
+ if (!PageIsolated(page))
list_del(&page->lru);
- }
}

/*
diff --git a/include/uapi/linux/magic.h b/include/uapi/linux/magic.h
index 0de181ad73d5..e1fbe72c39c0 100644
--- a/include/uapi/linux/magic.h
+++ b/include/uapi/linux/magic.h
@@ -78,5 +78,6 @@
#define BTRFS_TEST_MAGIC 0x73727279
#define NSFS_MAGIC 0x6e736673
#define BPF_FS_MAGIC 0xcafe4a11
+#define BALLOON_KVM_MAGIC 0x13661366

#endif /* __LINUX_MAGIC_H__ */
diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c
index 57b3e9bd6bc5..da91df50ba31 100644
--- a/mm/balloon_compaction.c
+++ b/mm/balloon_compaction.c
@@ -70,7 +70,7 @@ struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info)
*/
if (trylock_page(page)) {
#ifdef CONFIG_BALLOON_COMPACTION
- if (!PagePrivate(page)) {
+ if (PageIsolated(page)) {
/* raced with isolation */
unlock_page(page);
continue;
@@ -106,110 +106,50 @@ EXPORT_SYMBOL_GPL(balloon_page_dequeue);

#ifdef CONFIG_BALLOON_COMPACTION

-static inline void __isolate_balloon_page(struct page *page)
+bool balloon_page_isolate(struct page *page, isolate_mode_t mode)
+
{
struct balloon_dev_info *b_dev_info = balloon_page_device(page);
unsigned long flags;

spin_lock_irqsave(&b_dev_info->pages_lock, flags);
- ClearPagePrivate(page);
list_del(&page->lru);
b_dev_info->isolated_pages++;
spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
+
+ return true;
}

-static inline void __putback_balloon_page(struct page *page)
+void balloon_page_putback(struct page *page)
{
struct balloon_dev_info *b_dev_info = balloon_page_device(page);
unsigned long flags;

spin_lock_irqsave(&b_dev_info->pages_lock, flags);
- SetPagePrivate(page);
list_add(&page->lru, &b_dev_info->pages);
b_dev_info->isolated_pages--;
spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
}

-/* __isolate_lru_page() counterpart for a ballooned page */
-bool balloon_page_isolate(struct page *page)
-{
- /*
- * Avoid burning cycles with pages that are yet under __free_pages(),
- * or just got freed under us.
- *
- * In case we 'win' a race for a balloon page being freed under us and
- * raise its refcount preventing __free_pages() from doing its job
- * the put_page() at the end of this block will take care of
- * release this page, thus avoiding a nasty leakage.
- */
- if (likely(get_page_unless_zero(page))) {
- /*
- * As balloon pages are not isolated from LRU lists, concurrent
- * compaction threads can race against page migration functions
- * as well as race against the balloon driver releasing a page.
- *
- * In order to avoid having an already isolated balloon page
- * being (wrongly) re-isolated while it is under migration,
- * or to avoid attempting to isolate pages being released by
- * the balloon driver, lets be sure we have the page lock
- * before proceeding with the balloon page isolation steps.
- */
- if (likely(trylock_page(page))) {
- /*
- * A ballooned page, by default, has PagePrivate set.
- * Prevent concurrent compaction threads from isolating
- * an already isolated balloon page by clearing it.
- */
- if (balloon_page_movable(page)) {
- __isolate_balloon_page(page);
- unlock_page(page);
- return true;
- }
- unlock_page(page);
- }
- put_page(page);
- }
- return false;
-}
-
-/* putback_lru_page() counterpart for a ballooned page */
-void balloon_page_putback(struct page *page)
-{
- /*
- * 'lock_page()' stabilizes the page and prevents races against
- * concurrent isolation threads attempting to re-isolate it.
- */
- lock_page(page);
-
- if (__is_movable_balloon_page(page)) {
- __putback_balloon_page(page);
- /* drop the extra ref count taken for page isolation */
- put_page(page);
- } else {
- WARN_ON(1);
- dump_page(page, "not movable balloon page");
- }
- unlock_page(page);
-}

/* move_to_new_page() counterpart for a ballooned page */
-int balloon_page_migrate(struct page *newpage,
- struct page *page, enum migrate_mode mode)
+int balloon_page_migrate(struct address_space *mapping,
+ struct page *newpage, struct page *page,
+ enum migrate_mode mode)
{
struct balloon_dev_info *balloon = balloon_page_device(page);
- int rc = -EAGAIN;

VM_BUG_ON_PAGE(!PageLocked(page), page);
VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);

- if (WARN_ON(!__is_movable_balloon_page(page))) {
- dump_page(page, "not movable balloon page");
- return rc;
- }
+ return balloon->migratepage(balloon, newpage, page, mode);
+}

- if (balloon && balloon->migratepage)
- rc = balloon->migratepage(balloon, newpage, page, mode);
+const struct address_space_operations balloon_aops = {
+ .migratepage = balloon_page_migrate,
+ .isolate_page = balloon_page_isolate,
+ .putback_page = balloon_page_putback,
+};
+EXPORT_SYMBOL_GPL(balloon_aops);

- return rc;
-}
#endif /* CONFIG_BALLOON_COMPACTION */
diff --git a/mm/compaction.c b/mm/compaction.c
index 01789ebc4b10..adb805b01119 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -762,13 +762,6 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
*/
is_lru = PageLRU(page);
if (!is_lru) {
- if (unlikely(balloon_page_movable(page))) {
- if (balloon_page_isolate(page)) {
- /* Successfully isolated */
- goto isolate_success;
- }
- }
-
/*
* __PageMovable can return false positive so we need
* to verify it under page_lock.
diff --git a/mm/migrate.c b/mm/migrate.c
index b2ababa21440..df258cf38070 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -200,14 +200,12 @@ void putback_movable_pages(struct list_head *l)
list_del(&page->lru);
dec_zone_page_state(page, NR_ISOLATED_ANON +
page_is_file_cache(page));
- if (unlikely(isolated_balloon_page(page))) {
- balloon_page_putback(page);
/*
* We isolated non-lru movable page so here we can use
* __PageMovable because LRU page's mapping cannot have
* PAGE_MAPPING_MOVABLE.
*/
- } else if (unlikely(__PageMovable(page))) {
+ if (unlikely(__PageMovable(page))) {
VM_BUG_ON_PAGE(!PageIsolated(page), page);
lock_page(page);
if (PageMovable(page))
@@ -1036,18 +1034,6 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
if (unlikely(!trylock_page(newpage)))
goto out_unlock;

- if (unlikely(isolated_balloon_page(page))) {
- /*
- * A ballooned page does not need any special attention from
- * physical to virtual reverse mapping procedures.
- * Skip any attempt to unmap PTEs or to remap swap cache,
- * in order to avoid burning cycles at rmap level, and perform
- * the page migration right away (proteced by page lock).
- */
- rc = balloon_page_migrate(newpage, page, mode);
- goto out_unlock_both;
- }
-
if (unlikely(!is_lru)) {
rc = move_to_new_page(newpage, page, mode);
goto out_unlock_both;
@@ -1102,8 +1088,7 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
* list in here.
*/
if (rc == MIGRATEPAGE_SUCCESS) {
- if (unlikely(__is_movable_balloon_page(newpage) ||
- __PageMovable(newpage)))
+ if (unlikely(__PageMovable(newpage)))
put_page(newpage);
else
putback_lru_page(newpage);
diff --git a/mm/vmscan.c b/mm/vmscan.c
index fa36dd09eaa5..693ae62d236e 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1257,7 +1257,7 @@ unsigned long reclaim_clean_pages_from_list(struct zone *zone,

list_for_each_entry_safe(page, next, page_list, lru) {
if (page_is_file_cache(page) && !PageDirty(page) &&
- !isolated_balloon_page(page)) {
+ !__PageMovable(page)) {
ClearPageActive(page);
list_move(&page->lru, &clean_pages);
}
--
1.9.1