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Message-ID: <7ac7c0d8-4b7b-e362-08e7-6d62ee20f4c3@suse.cz>
Date: Fri, 7 Oct 2016 14:30:04 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Minchan Kim <minchan@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>
Cc: Mel Gorman <mgorman@...hsingularity.net>,
Joonsoo Kim <iamjoonsoo.kim@....com>,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
Sangseok Lee <sangseok.lee@....com>
Subject: Re: [PATCH 1/4] mm: adjust reserved highatomic count
On 10/07/2016 07:45 AM, Minchan Kim wrote:
> In page freeing path, migratetype is racy so that a highorderatomic
> page could free into non-highorderatomic free list.
Yes. If page from a pageblock went to a pcplist before that pageblock
was reserved as highatomic, free_pcppages_bulk() will misplace it.
> If that page
> is allocated, VM can change the pageblock from higorderatomic to
> something.
More specifically, steal_suitable_fallback(). Yes.
> In that case, we should adjust nr_reserved_highatomic.
> Otherwise, VM cannot reserve highorderatomic pageblocks any more
> although it doesn't reach 1% limit. It means highorder atomic
> allocation failure would be higher.
>
> So, this patch decreases the account as well as migratetype
> if it was MIGRATE_HIGHATOMIC.
>
> Signed-off-by: Minchan Kim <minchan@...nel.org>
Hm wouldn't it be simpler just to prevent the pageblock's migratetype to
be changed if it's highatomic? Possibly also not do
move_freepages_block() in that case. Most accurate would be to put such
misplaced page on the proper freelist and retry the fallback, but that
might be overkill.
> ---
> mm/page_alloc.c | 44 ++++++++++++++++++++++++++++++++++++++------
> 1 file changed, 38 insertions(+), 6 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 55ad0229ebf3..e7cbb3cc22fa 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -282,6 +282,9 @@ EXPORT_SYMBOL(nr_node_ids);
> EXPORT_SYMBOL(nr_online_nodes);
> #endif
>
> +static void dec_highatomic_pageblock(struct zone *zone, struct page *page,
> + int migratetype);
> +
> int page_group_by_mobility_disabled __read_mostly;
>
> #ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
> @@ -1935,7 +1938,14 @@ static void change_pageblock_range(struct page *pageblock_page,
> int nr_pageblocks = 1 << (start_order - pageblock_order);
>
> while (nr_pageblocks--) {
> - set_pageblock_migratetype(pageblock_page, migratetype);
> + if (get_pageblock_migratetype(pageblock_page) !=
> + MIGRATE_HIGHATOMIC)
> + set_pageblock_migratetype(pageblock_page,
> + migratetype);
> + else
> + dec_highatomic_pageblock(page_zone(pageblock_page),
> + pageblock_page,
> + migratetype);
> pageblock_page += pageblock_nr_pages;
> }
> }
> @@ -1996,8 +2006,14 @@ static void steal_suitable_fallback(struct zone *zone, struct page *page,
>
> /* Claim the whole block if over half of it is free */
> if (pages >= (1 << (pageblock_order-1)) ||
> - page_group_by_mobility_disabled)
> - set_pageblock_migratetype(page, start_type);
> + page_group_by_mobility_disabled) {
> + int mt = get_pageblock_migratetype(page);
> +
> + if (mt != MIGRATE_HIGHATOMIC)
> + set_pageblock_migratetype(page, start_type);
> + else
> + dec_highatomic_pageblock(zone, page, start_type);
> + }
> }
>
> /*
> @@ -2037,6 +2053,17 @@ int find_suitable_fallback(struct free_area *area, unsigned int order,
> return -1;
> }
>
> +static void dec_highatomic_pageblock(struct zone *zone, struct page *page,
> + int migratetype)
> +{
> + if (zone->nr_reserved_highatomic <= pageblock_nr_pages)
> + return;
> +
> + zone->nr_reserved_highatomic -= min(pageblock_nr_pages,
> + zone->nr_reserved_highatomic);
> + set_pageblock_migratetype(page, migratetype);
> +}
> +
> /*
> * Reserve a pageblock for exclusive use of high-order atomic allocations if
> * there are no empty page blocks that contain a page with a suitable order
> @@ -2555,9 +2582,14 @@ int __isolate_free_page(struct page *page, unsigned int order)
> struct page *endpage = page + (1 << order) - 1;
> for (; page < endpage; page += pageblock_nr_pages) {
> int mt = get_pageblock_migratetype(page);
> - if (!is_migrate_isolate(mt) && !is_migrate_cma(mt))
> - set_pageblock_migratetype(page,
> - MIGRATE_MOVABLE);
> + if (!is_migrate_isolate(mt) && !is_migrate_cma(mt)) {
> + if (mt != MIGRATE_HIGHATOMIC)
> + set_pageblock_migratetype(page,
> + MIGRATE_MOVABLE);
> + else
> + dec_highatomic_pageblock(zone, page,
> + MIGRATE_MOVABLE);
> + }
> }
> }
>
>
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