Re: [PATCH] mm: stop kswapd's infinite loop at high order allocation

[Nick Piggin]

On Tue, Dec 30, 2008 at 07:55:47PM +0900, KOSAKI Motohiro wrote:
> 
> ok, wassim confirmed this patch works well.
> 
> 
> ==
> From: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
> Subject: [PATCH] mm: kswapd stop infinite loop at high order allocation
> 
> Wassim Dagash reported following kswapd infinite loop problem.
> 
>   kswapd runs in some infinite loop trying to swap until order 10 of zone
>   highmem is OK, While zone higmem (as I understand) has nothing to do
>   with contiguous memory (cause there is no 1-1 mapping) which means
>   kswapd will continue to try to balance order 10 of zone highmem
>   forever (or until someone release a very large chunk of highmem).
> 
> He proposed remove contenious checking on highmem at all.
> However hugepage on highmem need contenious highmem page.
> 
> To add infinite loop stopper is simple and good.
> 
> 
> 
> Reported-by: wassim dagash <wassim.dagash@xxxxxxxxx>
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>

Thanks,

Reviewed-by: Nick Piggin <npiggin@xxxxxxx>

> ---
>  mm/vmscan.c |   11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> Index: b/mm/vmscan.c
> ===================================================================
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1872,6 +1872,17 @@ out:
>  
>  		try_to_freeze();
>  
> +		/*
> +		 * When highmem is very fragmented,
> +		 * alloc_pages(GFP_KERNEL, very-high-order) can cause
> +		 * infinite loop because zone_watermark_ok(highmem) failed.
> +		 * However, alloc_pages(GFP_KERNEL..) indicate highmem memory
> +		 * continuousness isn't necessary.
> +		 * Therefore we don't want contenious check at 2nd loop.
> +		 */
> +		if (nr_reclaimed < SWAP_CLUSTER_MAX)
> +			order = sc.order = 0;
> +
>  		goto loop_again;
>  	}
>  
> 
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