linux-kernel - Re: [UPDATE][PATCH v2 2/3] resource: Add release_mem_region

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Date:	Tue, 9 Apr 2013 12:51:41 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Toshi Kani <toshi.kani@...com>
Cc:	Ram Pai <linuxram@...ibm.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"guz.fnst@...fujitsu.com" <guz.fnst@...fujitsu.com>,
	"Makphaibulchoke, Thavatchai" <thavatchai.makpahibulchoke@...com>,
	"isimatu.yasuaki@...fujitsu.com" <isimatu.yasuaki@...fujitsu.com>,
	"wency@...fujitsu.com" <wency@...fujitsu.com>,
	"tangchen@...fujitsu.com" <tangchen@...fujitsu.com>,
	"jiang.liu@...wei.com" <jiang.liu@...wei.com>
Subject: Re: [UPDATE][PATCH v2 2/3] resource: Add
 release_mem_region_adjustable()

On Tue, 09 Apr 2013 13:02:30 -0600 Toshi Kani <toshi.kani@...com> wrote:

> > > +		/* look for the next resource if it does not fit into */
> > > +		if (res->start > start || res->end < end) {
> > > +			p = &res->sibling;
> > > +			continue;
> > > +		}
> > 
> > What if the resource overlaps. In other words, the res->start > start 
> > but res->end > end  ? 
> > 
> > Also do you handle the case where the range <start,end> spans
> > across multiple adjacent resources?
> 
> Good questions!  The two cases above are handled as error cases
> (-EINVAL) by design.  A requested region must either match exactly or
> fit into a single resource entry.  There are basically two design
> choices in release -- restrictive or non-restrictive.  Restrictive only
> releases under certain conditions, and non-restrictive releases under
> any conditions.  Since the existing release interfaces,
> __release_region() and __release_resource(), are restrictive, I intend
> to follow the same policy and made this new interface restrictive as
> well.  This new interface handles the common scenarios of memory
> hot-plug operations well.  I think your example cases are non-typical
> scenarios for memory hot-plug, and I am not sure if they happen under
> normal cases at this point.  Hence, they are handled as error cases for
> now.  We can always enhance this interface when we find them necessary
> to support as this interface is dedicated for memory hot-plug.  In other
> words, we should make such enhancement after we understand their
> scenarios well.  Does it make sense?

Can you please update the comment to describe the above?  Because if
one reviewer was wondering then later readers will also wonder.

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