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SubjectRe: [PATCH] add generic callbacks into compaction


2015-04-07 오전 9:59에 Minchan Kim 이(가) 쓴 글:
> 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?

Sure.

>
>>
>> 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.

OK. v2 will be:
int (*isolatepage)(struct address_space *, struct page *, enum migrate_mode);
int (*putbackpage)(struct address_space *, struct page *, enum migrate_mode);

>
>> +
>> 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?

Yes, it does. It is the common function to check the page migratable.

>
>> +
>> +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(...)"?

OK. What about __check_migrate_ops?

> 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?

I want to make a common framework to be able to support migrate/isolate/putback.
If you doesn't need any of it, you can make it empty function.
Is it irrational?

>
>> +{
>> + 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?

This is some depense code to check error.

>
>> + 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?

This also depense code.
I think depense code should check every case, doesn't 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.

OK. What about "mapping_driver_migratable"?
I will change other names like mapping_set_driver_migratable/mapping_clear_driver_migratable.

>
> 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.
>
>

I consider it as the second step.

>> + 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.

I assume that pages of driver without CPU mapping can be migratable.
So I add checking page_mapped zero.

>
>> +
>> /*
>> * 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.

I agree.
I'll test this patch enough and then proceed to it.

I do appreciate your feedback.

>
>> }
>> @@ -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
>>
>


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