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

[Gioh Kim <gioh.kim@lge.com>]

> On Mon, Jul 27, 2015 at 4:55 PM, Vlastimil Babka <vbabka@suse.cz> wrote:
>> 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.

You have a point.
Current 2/4 patch is lack of calling migrate/isolate.
It is not complete without 3/4.

I'll add calling migrate/isolate() at next spin.


>>
>>> 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?
>
> Well, I've suggested to name it "mobile" because there's already a lot of things
> called "movable". Mobile pages are special subset of movable pages: they
> are non-lru pages and define their own rules of moving in address
> space operations.
>
> Also there's a little pun: I guess main user will zram which is used
> mostly in embedded/mobile devices.

I like "mobile".
"movable" is for pages allocated with GFP_MOVABLE.
I think "movable" is a little ambiguous in this situation.

>
>>
>>> +
>>>          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.

I think compaction.c is suitable.

>>
>>
>>> +{
>>> +       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.
I got it.

>>
>>
>>> +{
>>> +       /*
>>> +        * '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>