Re: [PATCH 05/11] mm: mmzone: MIGRATE_CMA migration type added

["Michal Nazarewicz" <mina86@mina86.com>]

On Tue, 10 Jan 2012 15:38:36 +0100, Mel Gorman <mel@csn.ul.ie> wrote:

> On Thu, Dec 29, 2011 at 01:39:06PM +0100, Marek Szyprowski wrote:
>> From: Michal Nazarewicz <mina86@mina86.com>

>> @@ -35,13 +35,35 @@
>>   */
>>  #define PAGE_ALLOC_COSTLY_ORDER 3
>>
>> -#define MIGRATE_UNMOVABLE     0
>> -#define MIGRATE_RECLAIMABLE   1
>> -#define MIGRATE_MOVABLE       2
>> -#define MIGRATE_PCPTYPES      3 /* the number of types on the pcp lists */
>> -#define MIGRATE_RESERVE       3
>> -#define MIGRATE_ISOLATE       4 /* can't allocate from here */
>> -#define MIGRATE_TYPES         5
>> +enum {
>> +	MIGRATE_UNMOVABLE,
>> +	MIGRATE_RECLAIMABLE,
>> +	MIGRATE_MOVABLE,
>> +	MIGRATE_PCPTYPES,	/* the number of types on the pcp lists */
>> +	MIGRATE_RESERVE = MIGRATE_PCPTYPES,
>> +	/*
>> +	 * MIGRATE_CMA migration type is designed to mimic the way
>> +	 * ZONE_MOVABLE works.  Only movable pages can be allocated
>> +	 * from MIGRATE_CMA pageblocks and page allocator never
>> +	 * implicitly change migration type of MIGRATE_CMA pageblock.
>> +	 *
>> +	 * The way to use it is to change migratetype of a range of
>> +	 * pageblocks to MIGRATE_CMA which can be done by
>> +	 * __free_pageblock_cma() function.  What is important though
>> +	 * is that a range of pageblocks must be aligned to
>> +	 * MAX_ORDER_NR_PAGES should biggest page be bigger then
>> +	 * a single pageblock.
>> +	 */
>> +	MIGRATE_CMA,
>> +	MIGRATE_ISOLATE,	/* can't allocate from here */
>> +	MIGRATE_TYPES
>> +};
>
> MIGRATE_CMA is being added whether or not CONFIG_CMA is set. This
> increases the size of the pageblock bitmap and where that is just 1 bit
> per pageblock in the system, it may be noticable on large machines.

Wasn't aware of that, will do.  In fact, in earlier versions in was done this way,
but resulted in more #ifdefs.

>
>> +
>> +#ifdef CONFIG_CMA
>> +#  define is_migrate_cma(migratetype) unlikely((migratetype) == MIGRATE_CMA)
>> +#else
>> +#  define is_migrate_cma(migratetype) false
>> +#endif

> Use static inlines.

I decide to use #define for the sake of situations like
is_migrate_cma(get_pageblock_migratetype(page)).  With a static inline it will have
to read pageblock's migrate type even if !CONFIG_CMA.  A macro gets rid of this
operation all together.

>>  #define for_each_migratetype_order(order, type) \
>>  	for (order = 0; order < MAX_ORDER; order++) \
>> @@ -54,6 +76,11 @@ static inline int get_pageblock_migratetype(struct page *page)
>>  	return get_pageblock_flags_group(page, PB_migrate, PB_migrate_end);
>>  }
>>
>> +static inline bool is_pageblock_cma(struct page *page)
>> +{
>> +	return is_migrate_cma(get_pageblock_migratetype(page));
>> +}
>> +
>
> This allows additional calls to get_pageblock_migratetype() even if
> CONFIG_CMA is not set.
>
>>  struct free_area {
>>  	struct list_head	free_list[MIGRATE_TYPES];
>>  	unsigned long		nr_free;
>> diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h
>> index d305080..af650db 100644
>> --- a/include/linux/page-isolation.h
>> +++ b/include/linux/page-isolation.h
>> @@ -37,4 +37,7 @@ extern void unset_migratetype_isolate(struct page *page);
>>  int alloc_contig_range(unsigned long start, unsigned long end);
>>  void free_contig_range(unsigned long pfn, unsigned nr_pages);
>>
>> +/* CMA stuff */
>> +extern void init_cma_reserved_pageblock(struct page *page);
>> +
>>  #endif
>> diff --git a/mm/Kconfig b/mm/Kconfig
>> index 011b110..e080cac 100644
>> --- a/mm/Kconfig
>> +++ b/mm/Kconfig
>> @@ -192,7 +192,7 @@ config COMPACTION
>>  config MIGRATION
>>  	bool "Page migration"
>>  	def_bool y
>> -	depends on NUMA || ARCH_ENABLE_MEMORY_HOTREMOVE || COMPACTION
>> +	depends on NUMA || ARCH_ENABLE_MEMORY_HOTREMOVE || COMPACTION || CMA
>>  	help
>>  	  Allows the migration of the physical location of pages of processes
>>  	  while the virtual addresses are not changed. This is useful in
>> diff --git a/mm/compaction.c b/mm/compaction.c
>> index 8733441..46783b4 100644
>> --- a/mm/compaction.c
>> +++ b/mm/compaction.c
>> @@ -21,6 +21,11 @@
>>  #define CREATE_TRACE_POINTS
>>  #include <trace/events/compaction.h>
>>
>> +static inline bool is_migrate_cma_or_movable(int migratetype)
>> +{
>> +	return is_migrate_cma(migratetype) || migratetype == MIGRATE_MOVABLE;
>> +}
>> +
>
> That is not a name that helps any. migrate_async_suitable() would be
> marginally better.
>
>>  /**
>>   * isolate_freepages_range() - isolate free pages, must hold zone->lock.
>>   * @zone:	Zone pages are in.
>> @@ -213,7 +218,7 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
>>  		 */
>>  		pageblock_nr = low_pfn >> pageblock_order;
>>  		if (!cc->sync && last_pageblock_nr != pageblock_nr &&
>> -				get_pageblock_migratetype(page) != MIGRATE_MOVABLE) {
>> +		    is_migrate_cma_or_movable(get_pageblock_migratetype(page))) {
>>  			low_pfn += pageblock_nr_pages;
>>  			low_pfn = ALIGN(low_pfn, pageblock_nr_pages) - 1;
>>  			last_pageblock_nr = pageblock_nr;
>
> I know I suggested migrate_async_suitable() here but the check may
> not even happen if CMA uses sync migration.

For CMA, we know that pageblock's migrate type is MIGRATE_CMA.

>
>> @@ -295,8 +300,8 @@ static bool suitable_migration_target(struct page *page)
>>  	if (PageBuddy(page) && page_order(page) >= pageblock_order)
>>  		return true;
>>
>> -	/* If the block is MIGRATE_MOVABLE, allow migration */
>> -	if (migratetype == MIGRATE_MOVABLE)
>> +	/* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
>> +	if (is_migrate_cma_or_movable(migratetype))
>>  		return true;
>>
>>  	/* Otherwise skip the block */
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 47b0a85..06a7861 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -722,6 +722,26 @@ void __meminit __free_pages_bootmem(struct page *page, unsigned int order)
>>  	}
>>  }
>>
>> +#ifdef CONFIG_CMA
>> +/*
>> + * Free whole pageblock and set it's migration type to MIGRATE_CMA.
>> + */
>> +void __init init_cma_reserved_pageblock(struct page *page)
>> +{
>> +	unsigned i = pageblock_nr_pages;
>> +	struct page *p = page;
>> +
>> +	do {
>> +		__ClearPageReserved(p);
>> +		set_page_count(p, 0);
>> +	} while (++p, --i);
>> +
>> +	set_page_refcounted(page);
>> +	set_pageblock_migratetype(page, MIGRATE_CMA);
>> +	__free_pages(page, pageblock_order);
>> +	totalram_pages += pageblock_nr_pages;
>> +}
>> +#endif
>>
>>  /*
>>   * The order of subdivision here is critical for the IO subsystem.
>> @@ -830,11 +850,10 @@ struct page *__rmqueue_smallest(struct zone *zone, unsigned int order,
>>   * This array describes the order lists are fallen back to when
>>   * the free lists for the desirable migrate type are depleted
>>   */
>> -static int fallbacks[MIGRATE_TYPES][MIGRATE_TYPES-1] = {
>> +static int fallbacks[MIGRATE_PCPTYPES][4] = {
>>  	[MIGRATE_UNMOVABLE]   = { MIGRATE_RECLAIMABLE, MIGRATE_MOVABLE,   MIGRATE_RESERVE },
>>  	[MIGRATE_RECLAIMABLE] = { MIGRATE_UNMOVABLE,   MIGRATE_MOVABLE,   MIGRATE_RESERVE },
>> -	[MIGRATE_MOVABLE]     = { MIGRATE_RECLAIMABLE, MIGRATE_UNMOVABLE, MIGRATE_RESERVE },
>> -	[MIGRATE_RESERVE]     = { MIGRATE_RESERVE,     MIGRATE_RESERVE,   MIGRATE_RESERVE }, /* Never used */
>> +	[MIGRATE_MOVABLE]     = { MIGRATE_RECLAIMABLE, MIGRATE_UNMOVABLE, MIGRATE_CMA    , MIGRATE_RESERVE },
>
> Why did you delete [MIGRATE_RESERVE] here?

It is never used anyway.

> It changes the array from being expressed in terms of MIGRATE_TYPES to
> being a hard-coded value.

I don't follow.  This is only used in code path that fills in pcp lists, so only
the first MIGRATE_PCPTYPES rows are used.

> I do not see the advantage and it's not clear how it is related to the patch.

No real advantages, I can revert that change.

-- 
Best regards,                                         _     _
.o. | Liege of Serenely Enlightened Majesty of      o' \,=./ `o
..o | Computer Science,  Michał “mina86” Nazarewicz    (o o)
ooo +----<email/xmpp: mpn@google.com>--------------ooO--(_)--Ooo--

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