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From: Michal Hocko <mhocko@suse.com>
To: David Hildenbrand <david@redhat.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	linux-hyperv@vger.kernel.org, xen-devel@lists.xenproject.org,
	linux-acpi@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>,
	Matthew Wilcox <willy@infradead.org>,
	Oscar Salvador <osalvador@suse.de>,
	Pankaj Gupta <pankaj.gupta.linux@gmail.com>,
	Wei Yang <richard.weiyang@linux.alibaba.com>,
	Alexander Duyck <alexander.h.duyck@linux.intel.com>,
	Mel Gorman <mgorman@techsingularity.net>,
	Dave Hansen <dave.hansen@intel.com>,
	Vlastimil Babka <vbabka@suse.cz>, Mike Rapoport <rppt@kernel.org>,
	Scott Cheloha <cheloha@linux.ibm.com>,
	Michael Ellerman <mpe@ellerman.id.au>
Subject: Re: [PATCH v2 3/5] mm/page_alloc: move pages to tail in move_to_free_list()
Date: Tue, 6 Oct 2020 14:12:24 +0200	[thread overview]
Message-ID: <20201006121224.GE29020@dhcp22.suse.cz> (raw)
In-Reply-To: <20201005121534.15649-4-david@redhat.com>

On Mon 05-10-20 14:15:32, David Hildenbrand wrote:
> Whenever we move pages between freelists via move_to_free_list()/
> move_freepages_block(), we don't actually touch the pages:
> 1. Page isolation doesn't actually touch the pages, it simply isolates
>    pageblocks and moves all free pages to the MIGRATE_ISOLATE freelist.
>    When undoing isolation, we move the pages back to the target list.
> 2. Page stealing (steal_suitable_fallback()) moves free pages directly
>    between lists without touching them.
> 3. reserve_highatomic_pageblock()/unreserve_highatomic_pageblock() moves
>    free pages directly between freelists without touching them.
> 
> We already place pages to the tail of the freelists when undoing isolation
> via __putback_isolated_page(), let's do it in any case (e.g., if order <=
> pageblock_order) and document the behavior. To simplify, let's move the
> pages to the tail for all move_to_free_list()/move_freepages_block() users.
> 
> In 2., the target list is empty, so there should be no change. In 3.,
> we might observe a change, however, highatomic is more concerned about
> allocations succeeding than cache hotness - if we ever realize this
> change degrades a workload, we can special-case this instance and add a
> proper comment.
> 
> This change results in all pages getting onlined via online_pages() to
> be placed to the tail of the freelist.
> 
> Reviewed-by: Oscar Salvador <osalvador@suse.de>
> Acked-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
> Reviewed-by: Wei Yang <richard.weiyang@linux.alibaba.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>
> Cc: Mel Gorman <mgorman@techsingularity.net>
> Cc: Michal Hocko <mhocko@kernel.org>
> Cc: Dave Hansen <dave.hansen@intel.com>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: Mike Rapoport <rppt@kernel.org>
> Cc: Scott Cheloha <cheloha@linux.ibm.com>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Signed-off-by: David Hildenbrand <david@redhat.com>

Much simpler!
Acked-by: Michal Hocko <mhocko@suse.com>

Thanks!

> ---
>  mm/page_alloc.c     | 10 +++++++---
>  mm/page_isolation.c |  5 +++++
>  2 files changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index df5ff0cd6df1..b187e46cf640 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -901,13 +901,17 @@ static inline void add_to_free_list_tail(struct page *page, struct zone *zone,
>  	area->nr_free++;
>  }
>  
> -/* Used for pages which are on another list */
> +/*
> + * Used for pages which are on another list. Move the pages to the tail
> + * of the list - so the moved pages won't immediately be considered for
> + * allocation again (e.g., optimization for memory onlining).
> + */
>  static inline void move_to_free_list(struct page *page, struct zone *zone,
>  				     unsigned int order, int migratetype)
>  {
>  	struct free_area *area = &zone->free_area[order];
>  
> -	list_move(&page->lru, &area->free_list[migratetype]);
> +	list_move_tail(&page->lru, &area->free_list[migratetype]);
>  }
>  
>  static inline void del_page_from_free_list(struct page *page, struct zone *zone,
> @@ -2340,7 +2344,7 @@ static inline struct page *__rmqueue_cma_fallback(struct zone *zone,
>  #endif
>  
>  /*
> - * Move the free pages in a range to the free lists of the requested type.
> + * Move the free pages in a range to the freelist tail of the requested type.
>   * Note that start_page and end_pages are not aligned on a pageblock
>   * boundary. If alignment is required, use move_freepages_block()
>   */
> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> index abfe26ad59fd..83692b937784 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -106,6 +106,11 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype)
>  	 * If we isolate freepage with more than pageblock_order, there
>  	 * should be no freepage in the range, so we could avoid costly
>  	 * pageblock scanning for freepage moving.
> +	 *
> +	 * We didn't actually touch any of the isolated pages, so place them
> +	 * to the tail of the freelist. This is an optimization for memory
> +	 * onlining - just onlined memory won't immediately be considered for
> +	 * allocation.
>  	 */
>  	if (!isolated_page) {
>  		nr_pages = move_freepages_block(zone, page, migratetype, NULL);
> -- 
> 2.26.2

-- 
Michal Hocko
SUSE Labs

  reply	other threads:[~2020-10-06 12:12 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-05 12:15 [PATCH v2 0/5] mm: place pages to the freelist tail when onlining and undoing isolation David Hildenbrand
2020-10-05 12:15 ` [PATCH v2 1/5] mm/page_alloc: convert "report" flag of __free_one_page() to a proper flag David Hildenbrand
2020-10-05 12:15 ` [PATCH v2 2/5] mm/page_alloc: place pages to tail in __putback_isolated_page() David Hildenbrand
2020-10-20 17:18   ` Vlastimil Babka
2020-10-05 12:15 ` [PATCH v2 3/5] mm/page_alloc: move pages to tail in move_to_free_list() David Hildenbrand
2020-10-06 12:12   ` Michal Hocko [this message]
2020-10-20 17:20   ` Vlastimil Babka
2020-10-05 12:15 ` [PATCH v2 4/5] mm/page_alloc: place pages to tail in __free_pages_core() David Hildenbrand
2021-09-07 22:40   ` Sean Anderson
2021-09-08  6:21     ` David Hildenbrand
2021-09-10 23:06       ` Sean Anderson
2020-10-05 12:15 ` [PATCH v2 5/5] mm/memory_hotplug: update comment regarding zone shuffling David Hildenbrand
2020-10-20 17:21   ` Vlastimil Babka
2020-10-21 10:58   ` Pankaj Gupta

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