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Date: Tue, 28 Jul 2015 09:21:32 +0900
From: Gioh Kim <gioh.kim@....com>
To: Konstantin Khlebnikov <koct9i@...il.com>,
Vlastimil Babka <vbabka@...e.cz>
CC: Jeff Layton <jlayton@...chiereds.net>,
Bruce Fields <bfields@...ldses.org>,
Joonsoo Kim <iamjoonsoo.kim@....com>,
Al Viro <viro@...iv.linux.org.uk>,
"Michael S. Tsirkin" <mst@...hat.com>,
Minchan Kim <minchan@...nel.org>,
Rafael Aquini <aquini@...hat.com>,
linux-fsdevel <linux-fsdevel@...r.kernel.org>,
virtualization@...ts.linux-foundation.org,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Linux API <linux-api@...r.kernel.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
dri-devel <dri-devel@...ts.freedesktop.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Gioh Kim <gurugio@...mail.net>
Subject: Re: [PATCH 2/4] mm/compaction: enable mobile-page migration
> On Mon, Jul 27, 2015 at 4:55 PM, Vlastimil Babka <vbabka@...e.cz> wrote:
>> On 07/13/2015 10:35 AM, Gioh Kim wrote:
>>>
>>> From: Gioh Kim <gurugio@...mail.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@....com>
>>> Acked-by: Rafael Aquini <aquini@...hat.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 */
>>>
>>
>
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