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Message-ID: <xa1tegjpeo17.fsf@mina86.com>
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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