Re: [PATCH 2/4] mm/compaction: enable mobile-page migration

[Vlastimil Babka <vbabka@suse.cz>]

On 07/13/2015 10:35 AM, Gioh Kim wrote:
> From: Gioh Kim <gurugio@hanmail.net>
>
> Add framework to register callback functions and check page mobility.
> There are some modes for page isolation so that isolate interface
> has arguments of page address and isolation mode while putback
> interface has only page address as argument.

Note that unlike what subject suggest, this doesn't really enable 
mobile-page migration inside compaction, since that only happens with 
patch 3. This might theoretically affect some cherry-pick backports that 
don't care about balloon pages. I can imagine that can easily happen in 
the world of mobile devices?
It would thus be somewhat cleaner if this patch was complete in that sense.

> Signed-off-by: Gioh Kim <gioh.kim@lge.com>
> Acked-by: Rafael Aquini <aquini@redhat.com>
> ---
>   fs/proc/page.c                         |  3 ++
>   include/linux/compaction.h             | 80 ++++++++++++++++++++++++++++++++++
>   include/linux/fs.h                     |  2 +
>   include/linux/page-flags.h             | 19 ++++++++
>   include/uapi/linux/kernel-page-flags.h |  1 +
>   5 files changed, 105 insertions(+)
>
> diff --git a/fs/proc/page.c b/fs/proc/page.c
> index 7eee2d8..a4f5a00 100644
> --- a/fs/proc/page.c
> +++ b/fs/proc/page.c
> @@ -146,6 +146,9 @@ u64 stable_page_flags(struct page *page)
>   	if (PageBalloon(page))
>   		u |= 1 << KPF_BALLOON;
>
> +	if (PageMobile(page))
> +		u |= 1 << KPF_MOBILE;

PageMovable() would probably be as good a name and correspond to 
MIGRATE_MOVABLE somewhat, unlike a completely new term. Whatever driver 
starts to using this should probably change allocation flags to allocate 
MIGRATE_MOVABLE, so that it works fine with what fragmentation avoidance 
expects. Guess I should have said that earlier, but can you still 
reconsider?

> +
>   	u |= kpf_copy_bit(k, KPF_LOCKED,	PG_locked);
>
>   	u |= kpf_copy_bit(k, KPF_SLAB,		PG_slab);
> diff --git a/include/linux/compaction.h b/include/linux/compaction.h
> index aa8f61c..f693072 100644
> --- a/include/linux/compaction.h
> +++ b/include/linux/compaction.h
> @@ -1,6 +1,9 @@
>   #ifndef _LINUX_COMPACTION_H
>   #define _LINUX_COMPACTION_H
>
> +#include <linux/page-flags.h>
> +#include <linux/pagemap.h>
> +
>   /* Return values for compact_zone() and try_to_compact_pages() */
>   /* compaction didn't start as it was deferred due to past failures */
>   #define COMPACT_DEFERRED	0
> @@ -51,6 +54,70 @@ extern void compaction_defer_reset(struct zone *zone, int order,
>   				bool alloc_success);
>   extern bool compaction_restarting(struct zone *zone, int order);
>
> +static inline bool mobile_page(struct page *page)
> +{
> +	return page->mapping &&	(PageMobile(page) || PageBalloon(page));
> +}

I would put this definition to linux/page-flags.h and rename it to 
page_mobile (or better page_movable()), which is more common ordering.

> +
> +static inline bool isolate_mobilepage(struct page *page, isolate_mode_t mode)

Does this have to be in compaction.h? The only user is compaction.c so 
probably move it there, and if there ever is another module using this 
in the future, we can move it to a more appropriate place and declare it 
in e.g. mm/internal.h.

> +{
> +	bool ret = false;
> +
> +	/*
> +	 * 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 mobile 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 (unlikely(!get_page_unless_zero(page)))
> +		goto out;
> +
> +	/*
> +	 * As mobile pages are not isolated from LRU lists, concurrent
> +	 * compaction threads can race against page migration functions
> +	 * as well as race against the releasing a page.
> +	 *
> +	 * In order to avoid having an already isolated mobile page
> +	 * being (wrongly) re-isolated while it is under migration,
> +	 * or to avoid attempting to isolate pages being released,
> +	 * lets be sure we have the page lock
> +	 * before proceeding with the mobile page isolation steps.
> +	 */
> +	if (unlikely(!trylock_page(page)))
> +		goto out_putpage;
> +
> +	if (!(mobile_page(page) && page->mapping->a_ops->isolatepage))
> +		goto out_not_isolated;
> +	ret = page->mapping->a_ops->isolatepage(page, mode);
> +	if (!ret)
> +		goto out_not_isolated;
> +	unlock_page(page);
> +	return ret;
> +
> +out_not_isolated:
> +	unlock_page(page);
> +out_putpage:
> +	put_page(page);
> +out:
> +	return ret;
> +}
> +
> +static inline void putback_mobilepage(struct page *page)

Likewise, this could go to migrate.c. Or maybe together with 
isolate_mobilepage() if you don't want to split them.

> +{
> +	/*
> +	 * 'lock_page()' stabilizes the page and prevents races against
> +	 * concurrent isolation threads attempting to re-isolate it.
> +	 */
> +	lock_page(page);
> +	if (page->mapping && page->mapping->a_ops->putbackpage)
> +		page->mapping->a_ops->putbackpage(page);
> +	unlock_page(page);
> +	/* drop the extra ref count taken for mobile page isolation */
> +	put_page(page);
> +}
>   #else
>   static inline unsigned long try_to_compact_pages(gfp_t gfp_mask,
>   			unsigned int order, int alloc_flags,
> @@ -83,6 +150,19 @@ static inline bool compaction_deferred(struct zone *zone, int order)
>   	return true;
>   }
>
> +static inline bool mobile_page(struct page *page)
> +{
> +	return false;
> +}
> +
> +static inline bool isolate_mobilepage(struct page *page, isolate_mode_t mode)
> +{
> +	return false;
> +}
> +
> +static inline void putback_mobilepage(struct page *page)
> +{
> +}
>   #endif /* CONFIG_COMPACTION */
>
>   #if defined(CONFIG_COMPACTION) && defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index a0653e5..2cc4b24 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -396,6 +396,8 @@ struct address_space_operations {
>   	 */
>   	int (*migratepage) (struct address_space *,
>   			struct page *, struct page *, enum migrate_mode);
> +	bool (*isolatepage) (struct page *, isolate_mode_t);
> +	void (*putbackpage) (struct page *);
>   	int (*launder_page) (struct page *);
>   	int (*is_partially_uptodate) (struct page *, unsigned long,
>   					unsigned long);
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index f34e040..abef145 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -582,6 +582,25 @@ static inline void __ClearPageBalloon(struct page *page)
>   	atomic_set(&page->_mapcount, -1);
>   }
>
> +#define PAGE_MOBILE_MAPCOUNT_VALUE (-255)
> +
> +static inline int PageMobile(struct page *page)
> +{
> +	return atomic_read(&page->_mapcount) == PAGE_MOBILE_MAPCOUNT_VALUE;
> +}
> +
> +static inline void __SetPageMobile(struct page *page)
> +{
> +	VM_BUG_ON_PAGE(atomic_read(&page->_mapcount) != -1, page);
> +	atomic_set(&page->_mapcount, PAGE_MOBILE_MAPCOUNT_VALUE);
> +}
> +
> +static inline void __ClearPageMobile(struct page *page)
> +{
> +	VM_BUG_ON_PAGE(!PageMobile(page), page);
> +	atomic_set(&page->_mapcount, -1);
> +}
> +
>   /*
>    * If network-based swap is enabled, sl*b must keep track of whether pages
>    * were allocated from pfmemalloc reserves.
> diff --git a/include/uapi/linux/kernel-page-flags.h b/include/uapi/linux/kernel-page-flags.h
> index a6c4962..d50d9e8 100644
> --- a/include/uapi/linux/kernel-page-flags.h
> +++ b/include/uapi/linux/kernel-page-flags.h
> @@ -33,6 +33,7 @@
>   #define KPF_THP			22
>   #define KPF_BALLOON		23
>   #define KPF_ZERO_PAGE		24
> +#define KPF_MOBILE		25
>
>
>   #endif /* _UAPILINUX_KERNEL_PAGE_FLAGS_H */
>

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>