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

[David Rientjes <rientjes@google.com>]

On Tue, 27 Oct 2009, Andrew Morton wrote:

> > 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?
> 

Giving rt tasks access to memory reserves is necessary to reduce latency, 
the privilege does not apply to interrupts that subsequently get run on 
the same cpu.

> 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?
> 

Allowing interrupts to allocate below the low watermark when not 
GFP_ATOMIC depletes memory reserves; this fixes an inconsistency 
introduced by the page allocator refactoring patchset that went into 
2.6.31.

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