Re: [PATCH v3 4/5][RESEND] page_alloc: Make movablecore_map has higherpriority

[Tang Chen]

Hi Simon,

Thanks for reviewing. This logic is aimed at make movablecore_map
coexist with kernelcore/movablecore.

Please see below. :)

On 12/12/2012 09:33 AM, Simon Jeons wrote:
> > @@ -4839,9 +4839,17 @@ static void __init find_zone_movable_pfns_for_nodes(void)
> >   		required_kernelcore = max(required_kernelcore, corepages);
> >   	}
> >
> > -	/* If kernelcore was not specified, there is no ZONE_MOVABLE */
> > -	if (!required_kernelcore)
> > +	/*
> > +	 * If neither kernelcore/movablecore nor movablecore_map is specified,
> > +	 * there is no ZONE_MOVABLE. But if movablecore_map is specified, the
> > +	 * start pfn of ZONE_MOVABLE has been stored in zone_movable_limit[].
> > +	 */
> > +	if (!required_kernelcore) {
> > +		if (movablecore_map.nr_map)
> > +			memcpy(zone_movable_pfn, zone_movable_limit,
> > +				sizeof(zone_movable_pfn));

If users didn't specified kernelcore option, then zone_movable_pfn[]
and zone_movable_limit[] are all the same. We skip the logic.

> >   		goto out;
> > +	}
> >
> >   	/* usable_startpfn is the lowest possible pfn ZONE_MOVABLE can be at */
> >   	usable_startpfn = arch_zone_lowest_possible_pfn[movable_zone];
> > @@ -4871,10 +4879,24 @@ restart:
> >   		for_each_mem_pfn_range(i, nid,&start_pfn,&end_pfn, NULL) {
> >   			unsigned long size_pages;
> >
> > +			/*
> > +			 * Find more memory for kernelcore in
> > +			 * [zone_movable_pfn[nid], zone_movable_limit[nid]).
> > +			 */
> >   			start_pfn = max(start_pfn, zone_movable_pfn[nid]);
> >   			if (start_pfn>= end_pfn)
> >   				continue;
>
> Hi Chen,
>
> > +			if (zone_movable_limit[nid]) {

If users didn't give any limitation of ZONE_MOVABLE on node i, we could
skip the logic too.

> > +				end_pfn = min(end_pfn, zone_movable_limit[nid]);

In order to reuse the original kernelcore/movablecore logic, we keep
end_pfn <= zone_movable_limit[nid]. We device [start_pfn, end_pfn) into
two parts:
[start_pfn, zone_movable_limit[nid])
and
[zone_movable_limit[nid], end_pfn).

We just remove the second part, and go on to the original logic.

> > +				/* No range left for kernelcore in this node */
> > +				if (start_pfn>= end_pfn) {

Since we re-evaluated end_pfn, if we have crossed the limitation, we
should stop.

> > +					zone_movable_pfn[nid] =
> > +							zone_movable_limit[nid];

Here, we found the real limitation. That means, the lowest pfn of
ZONE_MOVABLE is either zone_movable_limit[nid] or the value the original
logic calculates out, which is below zone_movable_limit[nid].

> > +					break;

Then we break and go on to the next node.

> > +				}
> > +			}
> > +
>
> Could you explain this part of codes? hard to understand.
>
> >   			/* Account for what is only usable for kernelcore */
> >   			if (start_pfn<  usable_startpfn) {
> >   				unsigned long kernel_pages;
> > @@ -4934,12 +4956,12 @@ restart:
> >   	if (usable_nodes&&  required_kernelcore>  usable_nodes)
> >   		goto restart;
> >
> > +out:
> >   	/* Align start of ZONE_MOVABLE on all nids to MAX_ORDER_NR_PAGES */
> >   	for (nid = 0; nid<  MAX_NUMNODES; nid++)
> >   		zone_movable_pfn[nid] =
> >   			roundup(zone_movable_pfn[nid], MAX_ORDER_NR_PAGES);
> >
> > -out:
> >   	/* restore the node_state */
> >   	node_states[N_HIGH_MEMORY] = saved_node_state;
> >   }

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