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SubjectRe: [PATCH] add generic callbacks into compaction
Hello Gioh,

I wanted to have such feature for zsmalloc.
Thanks for the work.

On Wed, Apr 01, 2015 at 08:11:30AM +0900, Gioh Kim wrote:
> I sent a patch about page allocation for less fragmentation.
> http://permalink.gmane.org/gmane.linux.kernel.mm/130599
>
> It proposes a page allocator allocates pages in the same pageblock
> for the drivers to move their unmovable pages. Some drivers which comsumes many pages
> and increases system fragmentation use the allocator to move their pages to
> decrease fragmentation.
>
> I think I can try another approach.
> There is a compaction code for balloon pages.
> But the compaction code cannot migrate pages of other drivers.
> If there is a generic migration framework applicable to any drivers,
> drivers can register their migration functions.
> And the compaction can migrate movable pages and also driver's pages.
>
> I'm not familiar with virtualization so I couldn't test this patch yet.
> But if mm developers agree with this approach, I will complete this patch.
>
> I would do appreciate any feedback.

Could you separate introducing migrate core patchset and balloon patchset for
using the feature?

>
> Signed-off-by: Gioh Kim <gioh.kim@lge.com>
> ---
> drivers/virtio/virtio_balloon.c | 2 ++
> include/linux/balloon_compaction.h | 23 +++++++++---
> include/linux/fs.h | 3 ++
> include/linux/pagemap.h | 26 ++++++++++++++
> mm/balloon_compaction.c | 68 ++++++++++++++++++++++++++++++++++--
> mm/compaction.c | 7 ++--
> mm/migrate.c | 24 ++++++-------
> 7 files changed, 129 insertions(+), 24 deletions(-)
>
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 0413157..cd9b8e4 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -486,6 +486,8 @@ static int virtballoon_probe(struct virtio_device *vdev)
>
> balloon_devinfo_init(&vb->vb_dev_info);
> #ifdef CONFIG_BALLOON_COMPACTION
> + vb->vb_dev_info.mapping = balloon_mapping_alloc(&vb->vb_dev_info,
> + &balloon_aops);
> vb->vb_dev_info.migratepage = virtballoon_migratepage;
> #endif
>
> diff --git a/include/linux/balloon_compaction.h b/include/linux/balloon_compaction.h
> index 9b0a15d..0af32b3 100644
> --- a/include/linux/balloon_compaction.h
> +++ b/include/linux/balloon_compaction.h
> @@ -62,6 +62,7 @@ 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 address_space *mapping;
> };
>
> extern struct page *balloon_page_enqueue(struct balloon_dev_info *b_dev_info);
> @@ -76,10 +77,22 @@ static inline void balloon_devinfo_init(struct balloon_dev_info *balloon)
> }
>
> #ifdef CONFIG_BALLOON_COMPACTION
> -extern bool balloon_page_isolate(struct page *page);
> -extern void balloon_page_putback(struct page *page);
> -extern int balloon_page_migrate(struct page *newpage,
> - struct page *page, enum migrate_mode mode);
> +extern const struct address_space_operations balloon_aops;
> +extern int balloon_page_isolate(struct page *page);
> +extern int balloon_page_putback(struct page *page);
> +extern int balloon_page_migrate(struct address_space *mapping,
> + struct page *newpage,
> + struct page *page,
> + enum migrate_mode mode);
> +
> +extern struct address_space
> +*balloon_mapping_alloc(struct balloon_dev_info *b_dev_info,
> + const struct address_space_operations *a_ops);
> +
> +static inline void balloon_mapping_free(struct address_space *balloon_mapping)
> +{
> + kfree(balloon_mapping);
> +}
>
> /*
> * __is_movable_balloon_page - helper to perform @page PageBalloon tests
> @@ -123,6 +136,7 @@ static inline bool isolated_balloon_page(struct page *page)
> static inline void balloon_page_insert(struct balloon_dev_info *balloon,
> struct page *page)
> {
> + page->mapping = balloon->mapping;
> __SetPageBalloon(page);
> SetPagePrivate(page);
> set_page_private(page, (unsigned long)balloon);
> @@ -139,6 +153,7 @@ static inline void balloon_page_insert(struct balloon_dev_info *balloon,
> */
> static inline void balloon_page_delete(struct page *page)
> {
> + page->mapping = NULL;
> __ClearPageBalloon(page);
> set_page_private(page, 0);
> if (PagePrivate(page)) {
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index b4d71b5..de463b9 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -368,6 +368,9 @@ struct address_space_operations {
> */
> int (*migratepage) (struct address_space *,
> struct page *, struct page *, enum migrate_mode);
> + int (*isolatepage)(struct page *);

It would be useful if isolatepage is aware of migrate_mode and address_space
For exmaple, if it is MIGRATE_SYNC, driver could wait some of work to finish.
From address_space, driver can get private data registered when isolate/putback
happens.


> + int (*putbackpage)(struct page *);

Ditto.

> +
> int (*launder_page) (struct page *);
> int (*is_partially_uptodate) (struct page *, unsigned long,
> unsigned long);
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index 4b3736f..715b5b2 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -25,6 +25,7 @@ enum mapping_flags {
> AS_MM_ALL_LOCKS = __GFP_BITS_SHIFT + 2, /* under mm_take_all_locks() */
> AS_UNEVICTABLE = __GFP_BITS_SHIFT + 3, /* e.g., ramdisk, SHM_LOCK */
> AS_EXITING = __GFP_BITS_SHIFT + 4, /* final truncate in progress */
> + AS_MIGRATABLE = __GFP_BITS_SHIFT + 5,
> };
>
> static inline void mapping_set_error(struct address_space *mapping, int error)
> @@ -54,6 +55,31 @@ static inline int mapping_unevictable(struct address_space *mapping)
> return !!mapping;
> }
>
> +static inline void mapping_set_migratable(struct address_space *mapping)
> +{
> + set_bit(AS_MIGRATABLE, &mapping->flags);
> +}

It means every address_space which want to migrate pages mapped the address space
should call this function?

> +
> +static inline void mapping_clear_migratable(struct address_space *mapping)
> +{
> + clear_bit(AS_MIGRATABLE, &mapping->flags);
> +}
> +
> +static inline int __mapping_ops(struct address_space *mapping)

The naming of __mapping_ops is awkward. How about "bool is_migratable(...)"?
Another question:
Why should they support all fucntions of migrate(ie, migratepage, isolatepage, putbackpage).
I mean currently inode of regular file supports only migratepage.
By your rule, they are not migratable?

> +{
> + return mapping->a_ops &&
> + mapping->a_ops->migratepage &&
> + mapping->a_ops->isolatepage &&
> + mapping->a_ops->putbackpage;
> +}
> +
> +static inline int mapping_migratable(struct address_space *mapping)
> +{
> + if (mapping && __mapping_ops(mapping))

Why do we need mapping NULL check in here?
It's role of caller?

> + return test_bit(AS_MIGRATABLE, &mapping->flags);

It means some of address_space has migratepage, isolatepage, putbackpage but
it doesn't set AS_MIGRATABLE? Why do we need it?

> + return !!mapping;
> +}
> +
> static inline void mapping_set_exiting(struct address_space *mapping)
> {
> set_bit(AS_EXITING, &mapping->flags);
> diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c
> index fcad832..2e9d635 100644
> --- a/mm/balloon_compaction.c
> +++ b/mm/balloon_compaction.c
> @@ -131,8 +131,11 @@ static inline void __putback_balloon_page(struct page *page)
> }
>
> /* __isolate_lru_page() counterpart for a ballooned page */
> -bool balloon_page_isolate(struct page *page)
> +int balloon_page_isolate(struct page *page)
> {
> + if (!balloon_page_movable(page))
> + return false;
> +
> /*
> * Avoid burning cycles with pages that are yet under __free_pages(),
> * or just got freed under us.
> @@ -173,8 +176,11 @@ bool balloon_page_isolate(struct page *page)
> }
>
> /* putback_lru_page() counterpart for a ballooned page */
> -void balloon_page_putback(struct page *page)
> +int balloon_page_putback(struct page *page)
> {
> + if (!isolated_balloon_page(page))
> + return 0;
> +
> /*
> * 'lock_page()' stabilizes the page and prevents races against
> * concurrent isolation threads attempting to re-isolate it.
> @@ -190,15 +196,20 @@ void balloon_page_putback(struct page *page)
> dump_page(page, "not movable balloon page");
> }
> unlock_page(page);
> + return 0;
> }
>
> /* 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 0;
> +
> /*
> * Block others from accessing the 'newpage' when we get around to
> * establishing additional references. We should be the only one
> @@ -218,4 +229,55 @@ 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);
> +
> +struct address_space *balloon_mapping_alloc(struct balloon_dev_info *b_dev_info,
> + const struct address_space_operations *a_ops)
> +{
> + struct address_space *mapping;
> +
> + mapping = kmalloc(sizeof(*mapping), GFP_KERNEL);
> + if (!mapping)
> + return ERR_PTR(-ENOMEM);
> +
> + /*
> + * Give a clean 'zeroed' status to all elements of this special
> + * balloon page->mapping struct address_space instance.
> + */
> + address_space_init_once(mapping);
> +
> + /*
> + * Set mapping->flags appropriately, to allow balloon pages
> + * ->mapping identification.
> + */
> + mapping_set_migratable(mapping);
> + mapping_set_gfp_mask(mapping, balloon_mapping_gfp_mask());
> +
> + /* balloon's page->mapping->a_ops callback descriptor */
> + mapping->a_ops = a_ops;
> +
> + /*
> + * Establish a pointer reference back to the balloon device descriptor
> + * this particular page->mapping will be servicing.
> + * This is used by compaction / migration procedures to identify and
> + * access the balloon device pageset while isolating / migrating pages.
> + *
> + * As some balloon drivers can register multiple balloon devices
> + * for a single guest, this also helps compaction / migration to
> + * properly deal with multiple balloon pagesets, when required.
> + */
> + mapping->private_data = b_dev_info;
> + b_dev_info->mapping = mapping;
> +
> + return mapping;
> +}
> +EXPORT_SYMBOL_GPL(balloon_mapping_alloc);
> +
> #endif /* CONFIG_BALLOON_COMPACTION */
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 8c0d945..9fbcb7b 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -740,12 +740,9 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
> * Skip any other type of page
> */
> if (!PageLRU(page)) {
> - if (unlikely(balloon_page_movable(page))) {
> - if (balloon_page_isolate(page)) {
> - /* Successfully isolated */
> + if (mapping_migratable(page->mapping))

I see. Do you want to support this feature for only "non-LRU pages"?
Hmm, your term for functions was too generic so I got confused.
At least, it needs prefix like "special_xxx" so that we could classify
regular inode migrate and special driver migrate.

Otherwise, we could make logic more general so every address_space
want to migrate their page has all of migrate functions(ie, migrate,isolate,putback)
and we support default functions so addresss_space of regular inode will
have default functions while special driver overrides it by own functions.
With it, compact/migrate just calls registered function of each subsystem and
pass many role to them.


> + if (page->mapping->a_ops->isolatepage(page))
> goto isolate_success;
> - }
> - }
> continue;
> }
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 85e0426..37cb366 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -71,6 +71,12 @@ int migrate_prep_local(void)
> return 0;
> }
>
> +static bool isolated_migratable_page(struct page *page)
> +{
> + return page_mapped(page) == 0 &&
> + mapping_migratable(page->mapping);
> +}

Why does we need to check like this?
Whether isolate was successful or not depends on the driver.
We cannot expect it with only page_mapped.

> +
> /*
> * Put previously isolated pages back onto the appropriate lists
> * from where they were once taken off for compaction/migration.
> @@ -91,9 +97,9 @@ 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);
> + page_is_file_cache(page));
> + if (unlikely(isolated_migratable_page(page)))
> + page->mapping->a_ops->putbackpage(page);
> else
> putback_lru_page(page);

As I said, how about having putback_lru_page for page->mapping->a_ops->putbackpage
for regular inode? With it, we may remove some of branch in migrate/compact.c to
separate special driver and regular address_space.
Hope to enhance readability and make more flexible.

> }
> @@ -843,15 +849,9 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
> }
> }
>
> - 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);
> + if (unlikely(isolated_migratable_page(page))) {
> + rc = page->mapping->a_ops->migratepage(page->mapping,
> + newpage, page, mode);
> goto out_unlock;
> }
>
> --
> 1.7.9.5
>

--
Kind regards,
Minchan Kim


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