Re: [PATCH 3/3] mm: page allocator: Drain per-cpu lists after direct reclaim allocation fails

[KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>]

> When under significant memory pressure, a process enters direct reclaim
> and immediately afterwards tries to allocate a page. If it fails and no
> further progress is made, it's possible the system will go OOM. However,
> on systems with large amounts of memory, it's possible that a significant
> number of pages are on per-cpu lists and inaccessible to the calling
> process. This leads to a process entering direct reclaim more often than
> it should increasing the pressure on the system and compounding the problem.
> 
> This patch notes that if direct reclaim is making progress but
> allocations are still failing that the system is already under heavy
> pressure. In this case, it drains the per-cpu lists and tries the
> allocation a second time before continuing.
> 
> Signed-off-by: Mel Gorman <mel@csn.ul.ie>
> Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
> Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> ---
>  mm/page_alloc.c |   20 ++++++++++++++++----
>  1 files changed, 16 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index bbaa959..750e1dc 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1847,6 +1847,7 @@ __alloc_pages_direct_reclaim(gfp_t gfp_mask, unsigned int order,
>  	struct page *page = NULL;
>  	struct reclaim_state reclaim_state;
>  	struct task_struct *p = current;
> +	bool drained = false;
>  
>  	cond_resched();
>  
> @@ -1865,14 +1866,25 @@ __alloc_pages_direct_reclaim(gfp_t gfp_mask, unsigned int order,
>  
>  	cond_resched();
>  
> -	if (order != 0)
> -		drain_all_pages();
> +	if (unlikely(!(*did_some_progress)))
> +		return NULL;
>  
> -	if (likely(*did_some_progress))
> -		page = get_page_from_freelist(gfp_mask, nodemask, order,
> +retry:
> +	page = get_page_from_freelist(gfp_mask, nodemask, order,
>  					zonelist, high_zoneidx,
>  					alloc_flags, preferred_zone,
>  					migratetype);
> +
> +	/*
> +	 * If an allocation failed after direct reclaim, it could be because
> +	 * pages are pinned on the per-cpu lists. Drain them and try again
> +	 */
> +	if (!page && !drained) {
> +		drain_all_pages();
> +		drained = true;
> +		goto retry;
> +	}
> +
>  	return page;

I haven't read all of this patch series. (iow, this mail is luckly on top
of my mail box now) but at least I think this one is correct and good.

	Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>







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