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Message-ID: <CALYGNiMJ79HmLkoV_c2BR+ENig0h5aNzeY5YdS7kEYpFbLe=xA@mail.gmail.com>
Date: Mon, 27 Jul 2015 21:56:53 +0300
From: Konstantin Khlebnikov <koct9i@...il.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Gioh Kim <gioh.kim@....com>, 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.
>
>> 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.
>
>> +
>> 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 */
>>
>
--
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