linux-kernel - Re: [PATCH 1/4] mm: adjust reserved highatomic count

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Message-ID: <20161012053602.GA22174@techsingularity.net>
Date:   Wed, 12 Oct 2016 06:36:03 +0100
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Vlastimil Babka <vbabka@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        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 Tue, Oct 11, 2016 at 01:19:16PM +0900, Minchan Kim wrote:
> From 4a0b6a74ebf1af7f90720b0028da49e2e2a2b679 Mon Sep 17 00:00:00 2001
> From: Minchan Kim <minchan@...nel.org>
> Date: Thu, 6 Oct 2016 13:38:35 +0900
> Subject: [PATCH] mm: don't steal highatomic pageblock
> 
> In page freeing path, migratetype is racy so that a highorderatomic
> page could free into non-highorderatomic free list. If that page
> is allocated, VM can change the pageblock from higorderatomic to
> something. In that case, highatomic pageblock accounting is broken
> so it doesn't work(e.g., VM cannot reserve highorderatomic pageblocks
> any more although it doesn't reach 1% limit).
> 
> So, this patch prohibits the changing from highatomic to other type.
> It's no problem because MIGRATE_HIGHATOMIC is not listed in fallback
> array so stealing will only happen due to unexpected races which is
> really rare. Also, such prohibiting keeps highatomic pageblock more
> longer so it would be better for highorderatomic page allocation.
> 
> Signed-off-by: Minchan Kim <minchan@...nel.org>
> ---
>  mm/page_alloc.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 55ad0229ebf3..79853b258211 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2154,7 +2154,8 @@ __rmqueue_fallback(struct zone *zone, unsigned int order, int start_migratetype)
>  
>  		page = list_first_entry(&area->free_list[fallback_mt],
>  						struct page, lru);
> -		if (can_steal)
> +		if (can_steal &&
> +			get_pageblock_migratetype(page) != MIGRATE_HIGHATOMIC)
>  			steal_suitable_fallback(zone, page, start_migratetype);
>  
>  		/* Remove the page from the freelists */
> @@ -2555,7 +2556,8 @@ 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))
> +			if (!is_migrate_isolate(mt) && !is_migrate_cma(mt)
> +				&& mt != MIGRATE_HIGHATOMIC)
>  				set_pageblock_migratetype(page,
>  							  MIGRATE_MOVABLE);
>  		}

Acked-by: Mel Gorman <mgorman@...hsingularity.net>

-- 
Mel Gorman
SUSE Labs