Re: [PATCH 1/2] page allocator: Always wake kswapd when restarting an allocation attempt after direct reclaim failed

[Pekka Enberg <penberg@cs.helsinki.fi>]

On Fri, Oct 16, 2009 at 1:37 PM, Mel Gorman <mel@csn.ul.ie> wrote:
> If a direct reclaim makes no forward progress, it considers whether it
> should go OOM or not. Whether OOM is triggered or not, it may retry the
> application afterwards. In times past, this would always wake kswapd as well
> but currently, kswapd is not woken up after direct reclaim fails. For order-0
> allocations, this makes little difference but if there is a heavy mix of
> higher-order allocations that direct reclaim is failing for, it might mean
> that kswapd is not rewoken for higher orders as much as it did previously.
>
> This patch wakes up kswapd when an allocation is being retried after a direct
> reclaim failure. It would be expected that kswapd is already awake, but
> this has the effect of telling kswapd to reclaim at the higher order as well.
>
> Signed-off-by: Mel Gorman <mel@csn.ul.ie>

Reviewed-by: Pekka Enberg <penberg@cs.helsinki.fi>

> ---
>  mm/page_alloc.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index bf72055..dfa4362 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1817,9 +1817,9 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>        if (NUMA_BUILD && (gfp_mask & GFP_THISNODE) == GFP_THISNODE)
>                goto nopage;
>
> +restart:
>        wake_all_kswapd(order, zonelist, high_zoneidx);
>
> -restart:
>        /*
>         * OK, we're below the kswapd watermark and have kicked background
>         * reclaim. Now things get more complex, so set up alloc_flags according
> --
> 1.6.3.3
>
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