linux-kernel - Re: [PATCH v3 4/5][RESEND] page_alloc: Make movablecore

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Date:	Wed, 12 Dec 2012 19:56:27 -0600
From:	Simon Jeons <simon.jeons@...il.com>
To:	Tang Chen <tangchen@...fujitsu.com>
Cc:	jiang.liu@...wei.com, wujianguo@...wei.com, hpa@...or.com,
	akpm@...ux-foundation.org, wency@...fujitsu.com,
	laijs@...fujitsu.com, linfeng@...fujitsu.com, yinghai@...nel.org,
	isimatu.yasuaki@...fujitsu.com, rob@...dley.net,
	kosaki.motohiro@...fujitsu.com, minchan.kim@...il.com,
	mgorman@...e.de, rientjes@...gle.com, rusty@...tcorp.com.au,
	lliubbo@...il.com, jaegeuk.hanse@...il.com, tony.luck@...el.com,
	glommer@...allels.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH v3 4/5][RESEND] page_alloc: Make movablecore_map has
 higher priority

On Wed, 2012-12-12 at 17:34 +0800, Tang Chen wrote:
> Hi Simon,
> 
> Thanks for reviewing. This logic is aimed at make movablecore_map
> coexist with kernelcore/movablecore.
> 
> Please see below. :)

Hi Chen,

Thanks for your detail explanation. The logic looks reasonable to me. Bu
t how you guarantee the below changlog in your patchset.
1) If the range is involved in a single node, then from ss to the end of
the node will be ZONE_MOVABLE.
2) If the range covers two or more nodes, then from ss to the end of the
node will be ZONE_MOVABLE, and all the other nodes will only have
ZONE_MOVABLE.

> 
> 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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