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

From: Nick Piggin
Date: Tue Dec 30 2008 - 06:11:32 EST


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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