linux-kernel - Re: [PATCH] mm: avoid livelock on !__GFP

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Date:	Tue, 15 Nov 2011 13:40:42 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Mel Gorman <mgorman@...e.de>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Colin Cross <ccross@...roid.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH] mm: avoid livelock on !__GFP_FS allocations

On Mon, 14 Nov 2011, Mel Gorman wrote:

> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 9dd443d..5402897 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -127,6 +127,20 @@ void pm_restrict_gfp_mask(void)
>  	saved_gfp_mask = gfp_allowed_mask;
>  	gfp_allowed_mask &= ~GFP_IOFS;
>  }
> +
> +static bool pm_suspending(void)
> +{
> +	if ((gfp_allowed_mask & GFP_IOFS) == GFP_IOFS)
> +		return false;
> +	return true;
> +}
> +
> +#else
> +
> +static bool pm_suspending(void)
> +{
> +	return false;
> +}
>  #endif /* CONFIG_PM_SLEEP */
>  
>  #ifdef CONFIG_HUGETLB_PAGE_SIZE_VARIABLE
> @@ -2214,6 +2228,14 @@ rebalance:
>  
>  			goto restart;
>  		}
> +
> +		/*
> +		 * Suspend converts GFP_KERNEL to __GFP_WAIT which can
> +		 * prevent reclaim making forward progress without
> +		 * invoking OOM. Bail if we are suspending
> +		 */
> +		if (pm_suspending())
> +			goto nopage;
>  	}
>  
>  	/* Check if we should retry the allocation */

This allows all __GFP_NOFAIL allocations to fail while 
pm_restrict_gfp_mask() is in effect, so I disagree with this unless it is 
moved into the should_alloc_retry() logic.  If you pass did_some_progress 
into that function and then moved the check for __GFP_NOFAIL right under 
the check for __GFP_NORETRY and checked for pm_suspending() there (and 
before the check for PAGE_ALLOC_COSTLY_ORDER) then it would allow the 
infinite loop for __GFP_NOFAIL which is required if __GFP_WAIT.
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