linux-kernel - Re: [PATCH 1/4] mm, page_alloc: Split buffered

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Date:   Tue, 17 Jan 2017 21:07:49 +0000
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Jesper Dangaard Brouer <brouer@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Hillf Danton <hillf.zj@...baba-inc.com>,
        Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH 1/4] mm, page_alloc: Split buffered_rmqueue

On Tue, Jan 17, 2017 at 08:20:08PM +0000, Mel Gorman wrote:
> It's late so I'm fairly tired but assuming I can reproduce this in the
> morning, the first thing I'll try is something like this to force a reread
> of mems_allowed;
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index ebea51cc0135..3fc2b3a8d301 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3774,13 +3774,6 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
>  		.migratetype = gfpflags_to_migratetype(gfp_mask),
>  	};
>  
> -	if (cpusets_enabled()) {
> -		alloc_mask |= __GFP_HARDWALL;
> -		alloc_flags |= ALLOC_CPUSET;
> -		if (!ac.nodemask)
> -			ac.nodemask = &cpuset_current_mems_allowed;
> -	}
> -
>  	gfp_mask &= gfp_allowed_mask;
>  
>  	lockdep_trace_alloc(gfp_mask);
> @@ -3802,6 +3795,13 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
>  		alloc_flags |= ALLOC_CMA;
>  
>  retry_cpuset:
> +	if (cpusets_enabled()) {
> +		alloc_mask |= __GFP_HARDWALL;
> +		alloc_flags |= ALLOC_CPUSET;
> +		if (!nodemask)
> +			ac.nodemask = &cpuset_current_mems_allowed;
> +	}
> +
>  	cpuset_mems_cookie = read_mems_allowed_begin();
>  
>  	/* Dirty zone balancing only done in the fast path */
> 

I later recalled that we looked at this before and didn't think a reinit
was necessary because the location of cpuset_current_mems_allowed doesn't
change so I came back and took another look.  The location doesn't change
but after the first attempt, we reset ac.nodemask to the given nodemask and
don't recheck current_mems_allowed if the cpuset changed. The application
of memory policies versus cpusets is a mess so it'll take time to pick
apart to see if this is even remotely in the right direction.

-- 
Mel Gorman
SUSE Labs