Date:	Thu, 30 Jul 2015 16:08:20 +0200
From:	Michal Nazarewicz <mina86@...a86.com>
To:	Vlastimil Babka <vbabka@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org
Cc:	linux-kernel@...r.kernel.org,
	"minkyung88.kim" <minkyung88.kim@....com>, kmk3210@...il.com,
	Seungho Park <seungho1.park@....com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Minchan Kim <minchan@...nel.org>,
	Laura Abbott <lauraa@...eaurora.org>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Mel Gorman <mgorman@...e.de>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH 2/2] mm: rename and move get/set_freepage_migratetype

On Wed, Jul 22 2015, Vlastimil Babka wrote:
> Subject: mm: rename and move get/set_freepage_migratetype
>
> The pair of get/set_freepage_migratetype() functions are used to cache
> pageblock migratetype for a page put on a pcplist, so that it does not have
> to be retrieved again when the page is put on a free list (e.g. when pcplists
> become full). Historically it was also assumed that the value is accurate for
> pages on freelists (as the functions' names unfortunately suggest), but that
> cannot be guaranteed without affecting various allocator fast paths. It is in
> fact not needed and all such uses have been removed.
>
> The last two remaining (but pointless) usages related to pages of freelists
> are removed by this patch:
> - move_freepages() which operates on pages already on freelists
> - __free_pages_ok() which puts a page directly to freelist, bypassing pcplists
>
> To prevent further confusion, rename the functions to
> get/set_pcppage_migratetype() and expand their description. Since all the
> users are now in mm/page_alloc.c, move the functions there from the shared
> header.
>
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
> Acked-by: David Rientjes <rientjes@...gle.com>
> Cc: Joonsoo Kim <iamjoonsoo.kim@....com>
> Cc: Minchan Kim <minchan@...nel.org>
> Cc: Michal Nazarewicz <mina86@...a86.com>

Acked-by: Michal Nazarewicz <mina86@...a86.com>

> Cc: Laura Abbott <lauraa@...eaurora.org>
> Cc: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Cc: Mel Gorman <mgorman@...e.de>
> Cc: Johannes Weiner <hannes@...xchg.org>
> ---
>  include/linux/mm.h | 12 ------------
>  mm/page_alloc.c    | 41 ++++++++++++++++++++++++++++-------------
>  2 files changed, 28 insertions(+), 25 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index c3a2b37..ce36145 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -310,18 +310,6 @@ struct inode;
>  #define page_private(page)		((page)->private)
>  #define set_page_private(page, v)	((page)->private = (v))
>  
> -/* It's valid only if the page is free path or free_list */
> -static inline void set_freepage_migratetype(struct page *page, int migratetype)
> -{
> -	page->index = migratetype;
> -}
> -
> -/* It's valid only if the page is free path or free_list */
> -static inline int get_freepage_migratetype(struct page *page)
> -{
> -	return page->index;
> -}
> -
>  /*
>   * FIXME: take this include out, include page-flags.h in
>   * files which need it (119 of them)
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index c61fef8..4b220cb 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -125,6 +125,24 @@ unsigned long dirty_balance_reserve __read_mostly;
>  int percpu_pagelist_fraction;
>  gfp_t gfp_allowed_mask __read_mostly = GFP_BOOT_MASK;
>  
> +/*
> + * A cached value of the page's pageblock's migratetype, used when the page is
> + * put on a pcplist. Used to avoid the pageblock migratetype lookup when
> + * freeing from pcplists in most cases, at the cost of possibly becoming stale.
> + * Also the migratetype set in the page does not necessarily match the pcplist
> + * index, e.g. page might have MIGRATE_CMA set but be on a pcplist with any
> + * other index - this ensures that it will be put on the correct CMA freelist.
> + */
> +static inline int get_pcppage_migratetype(struct page *page)
> +{
> +	return page->index;
> +}
> +
> +static inline void set_pcppage_migratetype(struct page *page, int migratetype)
> +{
> +	page->index = migratetype;
> +}
> +
>  #ifdef CONFIG_PM_SLEEP
>  /*
>   * The following functions are used by the suspend/hibernate code to temporarily
> @@ -790,7 +808,7 @@ static void free_pcppages_bulk(struct zone *zone, int count,
>  			/* must delete as __free_one_page list manipulates */
>  			list_del(&page->lru);
>  
> -			mt = get_freepage_migratetype(page);
> +			mt = get_pcppage_migratetype(page);
>  			/* MIGRATE_ISOLATE page should not go to pcplists */
>  			VM_BUG_ON_PAGE(is_migrate_isolate(mt), page);
>  			/* Pageblock could have been isolated meanwhile */
> @@ -963,7 +981,6 @@ static void __free_pages_ok(struct page *page, unsigned int order)
>  	migratetype = get_pfnblock_migratetype(page, pfn);
>  	local_irq_save(flags);
>  	__count_vm_events(PGFREE, 1 << order);
> -	set_freepage_migratetype(page, migratetype);
>  	free_one_page(page_zone(page), page, pfn, order, migratetype);
>  	local_irq_restore(flags);
>  }
> @@ -1384,7 +1401,7 @@ struct page *__rmqueue_smallest(struct zone *zone, unsigned int order,
>  		rmv_page_order(page);
>  		area->nr_free--;
>  		expand(zone, page, order, current_order, area, migratetype);
> -		set_freepage_migratetype(page, migratetype);
> +		set_pcppage_migratetype(page, migratetype);
>  		return page;
>  	}
>  
> @@ -1461,7 +1478,6 @@ int move_freepages(struct zone *zone,
>  		order = page_order(page);
>  		list_move(&page->lru,
>  			  &zone->free_area[order].free_list[migratetype]);
> -		set_freepage_migratetype(page, migratetype);
>  		page += 1 << order;
>  		pages_moved += 1 << order;
>  	}
> @@ -1631,14 +1647,13 @@ __rmqueue_fallback(struct zone *zone, unsigned int order, int start_migratetype)
>  		expand(zone, page, order, current_order, area,
>  					start_migratetype);
>  		/*
> -		 * The freepage_migratetype may differ from pageblock's
> +		 * The pcppage_migratetype may differ from pageblock's
>  		 * migratetype depending on the decisions in
> -		 * try_to_steal_freepages(). This is OK as long as it
> -		 * does not differ for MIGRATE_CMA pageblocks. For CMA
> -		 * we need to make sure unallocated pages flushed from
> -		 * pcp lists are returned to the correct freelist.
> +		 * find_suitable_fallback(). This is OK as long as it does not
> +		 * differ for MIGRATE_CMA pageblocks. Those can be used as
> +		 * fallback only via special __rmqueue_cma_fallback() function
>  		 */
> -		set_freepage_migratetype(page, start_migratetype);
> +		set_pcppage_migratetype(page, start_migratetype);
>  
>  		trace_mm_page_alloc_extfrag(page, order, current_order,
>  			start_migratetype, fallback_mt);
> @@ -1714,7 +1729,7 @@ static int rmqueue_bulk(struct zone *zone, unsigned int order,
>  		else
>  			list_add_tail(&page->lru, list);
>  		list = &page->lru;
> -		if (is_migrate_cma(get_freepage_migratetype(page)))
> +		if (is_migrate_cma(get_pcppage_migratetype(page)))
>  			__mod_zone_page_state(zone, NR_FREE_CMA_PAGES,
>  					      -(1 << order));
>  	}
> @@ -1911,7 +1926,7 @@ void free_hot_cold_page(struct page *page, bool cold)
>  		return;
>  
>  	migratetype = get_pfnblock_migratetype(page, pfn);
> -	set_freepage_migratetype(page, migratetype);
> +	set_pcppage_migratetype(page, migratetype);
>  	local_irq_save(flags);
>  	__count_vm_event(PGFREE);
>  
> @@ -2116,7 +2131,7 @@ struct page *buffered_rmqueue(struct zone *preferred_zone,
>  		if (!page)
>  			goto failed;
>  		__mod_zone_freepage_state(zone, -(1 << order),
> -					  get_freepage_migratetype(page));
> +					  get_pcppage_migratetype(page));
>  	}
>  
>  	__mod_zone_page_state(zone, NR_ALLOC_BATCH, -(1 << order));
> -- 
> 2.4.5
>
>
>

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