Re: [PATCH 2/3] page allocator: Do not allow interrupts to use ALLOC_HARDER

[Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>]

On Tue, 27 Oct 2009 13:40:32 +0000
Mel Gorman <mel-wPRd99KPJ+uzQB+pC5nmwQ@public.gmane.org> wrote:

> Commit 341ce06f69abfafa31b9468410a13dbd60e2b237 altered watermark logic
> slightly by allowing rt_tasks that are handling an interrupt to set
> ALLOC_HARDER. This patch brings the watermark logic more in line with
> 2.6.30.
> 
> [rientjes-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org: Spotted the problem]
> Signed-off-by: Mel Gorman <mel-wPRd99KPJ+uzQB+pC5nmwQ@public.gmane.org>
> Reviewed-by: Pekka Enberg <penberg-bbCR+/B0CizivPeTLB3BmA@public.gmane.org>
> Reviewed-by: Rik van Riel <riel-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> Reviewed-by: KOSAKI Motohiro <kosaki.motohiro-+CUm20s59erQFUHtdCDX3A@public.gmane.org>
> ---
>  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 dfa4362..7f2aa3e 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1769,7 +1769,7 @@ gfp_to_alloc_flags(gfp_t gfp_mask)
>  		 * See also cpuset_zone_allowed() comment in kernel/cpuset.c.
>  		 */
>  		alloc_flags &= ~ALLOC_CPUSET;
> -	} else if (unlikely(rt_task(p)))
> +	} else if (unlikely(rt_task(p)) && !in_interrupt())
>  		alloc_flags |= ALLOC_HARDER;
>  
>  	if (likely(!(gfp_mask & __GFP_NOMEMALLOC))) {

What are the runtime-observeable effects of this change?

The description is a bit waffly-sounding for a -stable backportable
thing, IMO.  What reason do the -stable maintainers and users have to
believe that this patch is needed, and an improvement?