linux-kernel - Re: [PATCH v3 4/4] mm: make unreserve highatomic functions reliable

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Date:   Wed, 12 Oct 2016 10:36:53 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Vlastimil Babka <vbabka@...e.cz>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Sangseok Lee <sangseok.lee@....com>
Subject: Re: [PATCH v3 4/4] mm: make unreserve highatomic functions reliable

On Wed 12-10-16 17:03:49, Minchan Kim wrote:
> Currently, unreserve_highatomic_pageblock bails out if it found
> highatomic pageblock regardless of really moving free pages
> from the one so that it could mitigate unreserve logic's goal
> which saves OOM of a process.
> 
> This patch makes unreserve functions bail out only if it moves
> some pages out of !highatomic free list to avoid such false
> positive.
> 
> Another potential problem is that by race between page freeing and
> reserve highatomic function, pages could be in highatomic free list
> even though the pageblock is !high atomic migratetype. In that case,
> unreserve_highatomic_pageblock can be void if count of highatomic
> reserve is less than pageblock_nr_pages. We could solve it simply
> via draining all of reserved pages before the OOM. It would have
> a safeguard role to exhuast reserved pages before converging to OOM.
> 
> Signed-off-by: Minchan Kim <minchan@...nel.org>
> Signed-off-by: Michal Hocko <mhocko@...e.com>
> Acked-by: Vlastimil Babka <vbabka@...e.cz>

Looks good to me as well. If the previous one is agreed to go to stable
this one should go with it IMHO.

Thanks!

> ---
>  mm/page_alloc.c | 24 +++++++++++++++++-------
>  1 file changed, 17 insertions(+), 7 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index fd2f0e1bffc4..163d7fa759a2 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2079,8 +2079,12 @@ static void reserve_highatomic_pageblock(struct page *page, struct zone *zone,
>   * potentially hurts the reliability of high-order allocations when under
>   * intense memory pressure but failed atomic allocations should be easier
>   * to recover from than an OOM.
> + *
> + * If @force is true, try to unreserve a pageblock even though highatomic
> + * pageblock is exhausted.
>   */
> -static bool unreserve_highatomic_pageblock(const struct alloc_context *ac)
> +static bool unreserve_highatomic_pageblock(const struct alloc_context *ac,
> +						bool force)
>  {
>  	struct zonelist *zonelist = ac->zonelist;
>  	unsigned long flags;
> @@ -2092,8 +2096,12 @@ static bool unreserve_highatomic_pageblock(const struct alloc_context *ac)
>  
>  	for_each_zone_zonelist_nodemask(zone, z, zonelist, ac->high_zoneidx,
>  								ac->nodemask) {
> -		/* Preserve at least one pageblock */
> -		if (zone->nr_reserved_highatomic <= pageblock_nr_pages)
> +		/*
> +		 * Preserve at least one pageblock unless memory pressure
> +		 * is really high.
> +		 */
> +		if (!force && zone->nr_reserved_highatomic <=
> +					pageblock_nr_pages)
>  			continue;
>  
>  		spin_lock_irqsave(&zone->lock, flags);
> @@ -2138,8 +2146,10 @@ static bool unreserve_highatomic_pageblock(const struct alloc_context *ac)
>  			 */
>  			set_pageblock_migratetype(page, ac->migratetype);
>  			ret = move_freepages_block(zone, page, ac->migratetype);
> -			spin_unlock_irqrestore(&zone->lock, flags);
> -			return ret;
> +			if (ret) {
> +				spin_unlock_irqrestore(&zone->lock, flags);
> +				return ret;
> +			}
>  		}
>  		spin_unlock_irqrestore(&zone->lock, flags);
>  	}
> @@ -3343,7 +3353,7 @@ __alloc_pages_direct_reclaim(gfp_t gfp_mask, unsigned int order,
>  	 * Shrink them them and try again
>  	 */
>  	if (!page && !drained) {
> -		unreserve_highatomic_pageblock(ac);
> +		unreserve_highatomic_pageblock(ac, false);
>  		drain_all_pages(NULL);
>  		drained = true;
>  		goto retry;
> @@ -3462,7 +3472,7 @@ should_reclaim_retry(gfp_t gfp_mask, unsigned order,
>  	 */
>  	if (*no_progress_loops > MAX_RECLAIM_RETRIES) {
>  		/* Before OOM, exhaust highatomic_reserve */
> -		return unreserve_highatomic_pageblock(ac);
> +		return unreserve_highatomic_pageblock(ac, true);
>  	}
>  
>  	/*
> -- 
> 2.7.4
> 

-- 
Michal Hocko
SUSE Labs