Re: [patch 3/3] mm: page_alloc: fair zone allocator policy

[Rik van Riel]

On 07/22/2013 05:04 PM, Johannes Weiner wrote:
> On Mon, Jul 22, 2013 at 04:21:07PM -0400, Rik van Riel wrote:
> > On 07/19/2013 04:55 PM, Johannes Weiner wrote:
> >
> > > @@ -1984,7 +1992,8 @@ this_zone_full:
> > >   		goto zonelist_scan;
> > >   	}
> > >
> > > -	if (page)
> > > +	if (page) {
> > > +		atomic_sub(1U << order, &zone->alloc_batch);
> > >   		/*
> > >   		 * page->pfmemalloc is set when ALLOC_NO_WATERMARKS was
> > >   		 * necessary to allocate the page. The expectation is
> >
> > Could this be moved into the slow path in buffered_rmqueue and
> > rmqueue_bulk, or would the effect of ignoring the pcp buffers be
> > too detrimental to keeping the balance between zones?
>
> What I'm worried about is not the inaccury that comes from the buffer
> size but the fact that there are no guaranteed buffer empty+refill
> cycles.  The reclaimer could end up feeding the pcp list that the
> allocator is using indefinitely, which brings us back to the original
> problem.  If you have >= NR_CPU jobs running, the kswapds are bound to
> share CPUs with the allocating tasks, so the scenario is not unlikely.

You are absolutely right.  Thinking about it some more,
I cannot think of a better way to do this than your patch.

Reviewed-by: Rik van Riel <riel@xxxxxxxxxx>

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