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Commit 7cf91a98 authored by Joonsoo Kim's avatar Joonsoo Kim Committed by Linus Torvalds
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mm/compaction: speed up pageblock_pfn_to_page() when zone is contiguous 

There is a performance drop report due to hugepage allocation and in
there half of cpu time are spent on pageblock_pfn_to_page() in
compaction [1].

In that workload, compaction is triggered to make hugepage but most of
pageblocks are un-available for compaction due to pageblock type and
skip bit so compaction usually fails.  Most costly operations in this
case is to find valid pageblock while scanning whole zone range.  To
check if pageblock is valid to compact, valid pfn within pageblock is
required and we can obtain it by calling pageblock_pfn_to_page().  This
function checks whether pageblock is in a single zone and return valid
pfn if possible.  Problem is that we need to check it every time before
scanning pageblock even if we re-visit it and this turns out to be very
expensive in this workload.

Although we have no way to skip this pageblock check in the system where
hole exists at arbitrary position, we can use cached value for zone
continuity and just do pfn_to_page() in the system where hole doesn't
exist.  This optimization considerably speeds up in above workload.

Before vs After
  Max: 1096 MB/s vs 1325 MB/s
  Min: 635 MB/s 1015 MB/s
  Avg: 899 MB/s 1194 MB/s

Avg is improved by roughly 30% [2].

[1]: http://www.spinics.net/lists/linux-mm/msg97378.html
[2]: https://lkml.org/lkml/2015/12/9/23



[akpm@linux-foundation.org: don't forget to restore zone->contiguous on error path, per Vlastimil]
Signed-off-by: default avatarJoonsoo Kim <iamjoonsoo.kim@lge.com>
Reported-by: default avatarAaron Lu <aaron.lu@intel.com>
Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
Tested-by: default avatarAaron Lu <aaron.lu@intel.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent e1409c32

include/linux/gfp.h

+0 −6
Original line number Diff line number Diff line
@@ -519,13 +519,7 @@ void drain_zone_pages(struct zone *zone, struct per_cpu_pages *pcp); 
void drain_all_pages(struct zone *zone);

void drain_local_pages(struct zone *zone);



#ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT

void page_alloc_init_late(void);

#else

static inline void page_alloc_init_late(void)

{

}

#endif



/*

 * gfp_allowed_mask is set to GFP_BOOT_MASK during early boot to restrict what

include/linux/memory_hotplug.h

+3 −0
Original line number Diff line number Diff line
@@ -198,6 +198,9 @@ void put_online_mems(void); 
void mem_hotplug_begin(void);

void mem_hotplug_done(void);



extern void set_zone_contiguous(struct zone *zone);

extern void clear_zone_contiguous(struct zone *zone);



#else /* ! CONFIG_MEMORY_HOTPLUG */

/*

 * Stub functions for when hotplug is off

include/linux/mmzone.h

+2 −0
Original line number Diff line number Diff line
@@ -522,6 +522,8 @@ struct zone { 
	bool			compact_blockskip_flush;

#endif



	bool			contiguous;



	ZONE_PADDING(_pad3_)

	/* Zone statistics */

	atomic_long_t		vm_stat[NR_VM_ZONE_STAT_ITEMS];

mm/compaction.c

+0 −43
Original line number Diff line number Diff line
@@ -71,49 +71,6 @@ static inline bool migrate_async_suitable(int migratetype) 
	return is_migrate_cma(migratetype) || migratetype == MIGRATE_MOVABLE;

}



/*

 * Check that the whole (or subset of) a pageblock given by the interval of

 * [start_pfn, end_pfn) is valid and within the same zone, before scanning it

 * with the migration of free compaction scanner. The scanners then need to

 * use only pfn_valid_within() check for arches that allow holes within

 * pageblocks.

 *

 * Return struct page pointer of start_pfn, or NULL if checks were not passed.

 *

 * It's possible on some configurations to have a setup like node0 node1 node0

 * i.e. it's possible that all pages within a zones range of pages do not

 * belong to a single zone. We assume that a border between node0 and node1

 * can occur within a single pageblock, but not a node0 node1 node0

 * interleaving within a single pageblock. It is therefore sufficient to check

 * the first and last page of a pageblock and avoid checking each individual

 * page in a pageblock.

 */

static struct page *pageblock_pfn_to_page(unsigned long start_pfn,

				unsigned long end_pfn, struct zone *zone)

{

	struct page *start_page;

	struct page *end_page;



	/* end_pfn is one past the range we are checking */

	end_pfn--;



	if (!pfn_valid(start_pfn) || !pfn_valid(end_pfn))

		return NULL;



	start_page = pfn_to_page(start_pfn);



	if (page_zone(start_page) != zone)

		return NULL;



	end_page = pfn_to_page(end_pfn);



	/* This gives a shorter code than deriving page_zone(end_page) */

	if (page_zone_id(start_page) != page_zone_id(end_page))

		return NULL;



	return start_page;

}



#ifdef CONFIG_COMPACTION



/* Do not skip compaction more than 64 times */

mm/internal.h

+12 −0
Original line number Diff line number Diff line
@@ -132,6 +132,18 @@ __find_buddy_index(unsigned long page_idx, unsigned int order) 
	return page_idx ^ (1 << order);

}



extern struct page *__pageblock_pfn_to_page(unsigned long start_pfn,

				unsigned long end_pfn, struct zone *zone);



static inline struct page *pageblock_pfn_to_page(unsigned long start_pfn,

				unsigned long end_pfn, struct zone *zone)

{

	if (zone->contiguous)

		return pfn_to_page(start_pfn);



	return __pageblock_pfn_to_page(start_pfn, end_pfn, zone);

}



extern int __isolate_free_page(struct page *page, unsigned int order);

extern void __free_pages_bootmem(struct page *page, unsigned long pfn,

					unsigned int order);