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Date: Thu, 9 Jul 2015 11:07:05 +0300
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Gioh Kim <gioh.kim@....com>
Cc: jlayton@...chiereds.net, bfields@...ldses.org, vbabka@...e.cz,
iamjoonsoo.kim@....com, viro@...iv.linux.org.uk, koct9i@...il.com,
minchan@...nel.org, aquini@...hat.com,
linux-fsdevel@...r.kernel.org,
virtualization@...ts.linux-foundation.org,
linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
linux-mm@...ck.org, gunho.lee@....com, akpm@...ux-foundation.org,
Gioh Kim <gurugio@...mail.net>
Subject: Re: [RFCv3 3/5] mm/balloon: apply mobile page migratable into balloon
On Tue, Jul 07, 2015 at 01:36:23PM +0900, Gioh Kim wrote:
> From: Gioh Kim <gurugio@...mail.net>
>
> Apply mobile page migration into balloon driver.
> The balloong driver has an anonymous inode that manages
> address_space_operation for page migration.
>
> Signed-off-by: Gioh Kim <gioh.kim@....com>
> ---
> drivers/virtio/virtio_balloon.c | 3 ++
> include/linux/balloon_compaction.h | 15 +++++++--
> mm/balloon_compaction.c | 65 +++++++++++++-------------------------
> mm/compaction.c | 2 +-
> mm/migrate.c | 2 +-
> 5 files changed, 39 insertions(+), 48 deletions(-)
>
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 82e80e0..ef5b9b5 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -30,6 +30,7 @@
> #include <linux/balloon_compaction.h>
> #include <linux/oom.h>
> #include <linux/wait.h>
> +#include <linux/anon_inodes.h>
>
> /*
> * Balloon device works in 4K page units. So each page is pointed to by
> @@ -505,6 +506,8 @@ static int virtballoon_probe(struct virtio_device *vdev)
> balloon_devinfo_init(&vb->vb_dev_info);
> #ifdef CONFIG_BALLOON_COMPACTION
> vb->vb_dev_info.migratepage = virtballoon_migratepage;
> + vb->vb_dev_info.inode = anon_inode_new();
> + vb->vb_dev_info.inode->i_mapping->a_ops = &balloon_aops;
> #endif
>
> err = init_vqs(vb);
> diff --git a/include/linux/balloon_compaction.h b/include/linux/balloon_compaction.h
> index 9b0a15d..a9e0bde 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);
> @@ -73,12 +75,16 @@ 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);
>
> /*
> @@ -124,6 +130,7 @@ static inline void balloon_page_insert(struct balloon_dev_info *balloon,
> struct page *page)
> {
> __SetPageBalloon(page);
> + page->mapping = balloon->inode->i_mapping;
> SetPagePrivate(page);
> set_page_private(page, (unsigned long)balloon);
> list_add(&page->lru, &balloon->pages);
> @@ -140,6 +147,7 @@ static inline void balloon_page_insert(struct balloon_dev_info *balloon,
> static inline void balloon_page_delete(struct page *page)
> {
> __ClearPageBalloon(page);
> + page->mapping = NULL;
> set_page_private(page, 0);
> if (PagePrivate(page)) {
> ClearPagePrivate(page);
Order of cleanup here is not the reverse of the order of initialization.
Better make it exactly the reverse.
Also, I have a question: is it enough to lock the page to make changing
the mapping safe? Do all users lock the page too?
> @@ -191,7 +199,8 @@ static inline bool isolated_balloon_page(struct page *page)
> return false;
> }
>
> -static inline bool balloon_page_isolate(struct page *page)
> +static inline bool balloon_page_isolate(struct page *page,
> + isolate_mode_t mode)
> {
> return false;
> }
> diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c
> index fcad832..0dd0b0d 100644
> --- a/mm/balloon_compaction.c
> +++ b/mm/balloon_compaction.c
> @@ -131,43 +131,16 @@ static inline void __putback_balloon_page(struct page *page)
> }
>
> /* __isolate_lru_page() counterpart for a ballooned page */
> -bool balloon_page_isolate(struct page *page)
> +bool balloon_page_isolate(struct page *page, isolate_mode_t mode)
> {
> /*
> - * 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.
> + * A ballooned page, by default, has PagePrivate set.
> + * Prevent concurrent compaction threads from isolating
> + * an already isolated balloon page by clearing it.
> */
> - 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);
> + if (balloon_page_movable(page)) {
> + __isolate_balloon_page(page);
> + return true;
> }
> return false;
> }
> @@ -175,30 +148,28 @@ bool balloon_page_isolate(struct page *page)
> /* 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 (!isolated_balloon_page(page))
> + return;
>
> 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,
> +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;
>
> + if (!isolated_balloon_page(page))
> + return rc;
> +
> /*
> * Block others from accessing the 'newpage' when we get around to
> * establishing additional references. We should be the only one
> @@ -218,4 +189,12 @@ int balloon_page_migrate(struct page *newpage,
> unlock_page(newpage);
> return rc;
> }
> +
> +/* define the balloon_mapping->a_ops callback to allow balloon page migration */
> +const struct address_space_operations balloon_aops = {
> + .migratepage = balloon_page_migrate,
> + .isolatepage = balloon_page_isolate,
> + .putbackpage = balloon_page_putback,
> +};
> +EXPORT_SYMBOL_GPL(balloon_aops);
> #endif /* CONFIG_BALLOON_COMPACTION */
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 018f08d..81bafaf 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -719,7 +719,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
> */
> if (!PageLRU(page)) {
> if (unlikely(balloon_page_movable(page))) {
> - if (balloon_page_isolate(page)) {
> + if (balloon_page_isolate(page, isolate_mode)) {
> /* Successfully isolated */
> goto isolate_success;
> }
> diff --git a/mm/migrate.c b/mm/migrate.c
> index f53838f..c94038e 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -852,7 +852,7 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
> * 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);
> + rc = balloon_page_migrate(page->mapping, newpage, page, mode);
> goto out_unlock;
> }
>
> --
> 2.1.4
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