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

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Message-ID: <20130407040136.GA13533@ram.oc3035372033.ibm.com>
Date:	Sun, 7 Apr 2013 12:01:36 +0800
From:	Ram Pai <linuxram@...ibm.com>
To:	Toshi Kani <toshi.kani@...com>
Cc:	akpm@...ux-foundation.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, tmac@...com,
	isimatu.yasuaki@...fujitsu.com, wency@...fujitsu.com,
	tangchen@...fujitsu.com, jiang.liu@...wei.com
Subject: Re: [PATCH 2/3] resource: Add release_mem_region_adjustable()

On Thu, Apr 04, 2013 at 08:07:44AM -0600, Toshi Kani wrote:
> On Thu, 2013-04-04 at 14:48 +0800, Ram Pai wrote:
> > On Wed, Apr 03, 2013 at 01:55:05PM -0600, Toshi Kani wrote:
> > > On Wed, 2013-04-03 at 13:37 +0800, Ram Pai wrote:
> > > > On Tue, Apr 02, 2013 at 10:17:29AM -0600, Toshi Kani wrote:
> > > > > +	while ((res = *p)) {
> > 
> > ...snip...
> > 
> > > > > +		if (res->start > start || res->end < end) {
> > > > 
> > > > This check looks sub-optimal; possbily wrong, to me.  if the res->start
> > > > is greater than 'start', then obviously its sibling's start will
> > > > also be greater than 'start'. So it will loop through all the
> > > > resources unnecesarily.
> > > 
> > > I think this check is necessary to check if the requested range fits
> > > into a resource.  It needs to check both sides to verify this.  I will
> > > add some comment on this check.
> > > 
> > > >   you might want something like
> > > > 
> > > > 		if (start >= res->end) {
> > > 
> > > I agree that this list is sorted, so we can optimize an error case (i.e.
> > > no matching entry is found) with an additional check.  I will add the
> > > following check at the beginning of the while loop.  
> > > 
> > >                 if (res->start >= end)
> > >                         break;
> > > 
> > > I also realized that the function returns 0 when no matching entry is
> > > found.  I will change it to return -EINVAL as well.  
> > 
> > ok. this will take care of it.
> > 
> > > 
> > > > 		
> > > > > +			p = &res->sibling;
> > > > > +			continue;
> > > > > +		}
> > > > > +
> > > > > +		if (!(res->flags & IORESOURCE_MEM)) {
> > > > > +			ret = -EINVAL;
> > > > > +			break;
> > > > > +		}
> > > > > +
> > > > > +		if (!(res->flags & IORESOURCE_BUSY)) {
> > > > > +			p = &res->child;
> > > > > +			continue;
> > > > > +		}
> > > > > +
> > > > > +		if (res->start == start && res->end == end) {
> > > > > +			/* free the whole entry */
> > > > > +			*p = res->sibling;
> > > > > +			kfree(res);
> > > > 
> > > > This is incomplete. the prev resource's sibling should now point to
> > > > this resource's sibling. The parent's child has to be updated if
> > > > this resource is the first child resource. no?
> > > 
> > > If this resource is the first child, *p is set to &parent->child.  So,
> > > it will update the parents' child.
> > 
> > But if the resource is not the parent's first child? will it update the
> > previous siblings ->sibling ?
> 
> Yes.  When it continues in the while loop, p is set to &res->sibling.
> So, it will update the previous sibling's ->sibling.

You are right. It does update the pointers correctly. I mis-read the
code.
RP

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