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

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Date:	Thu, 04 Apr 2013 08:07:44 -0600
From:	Toshi Kani <toshi.kani@...com>
To:	Ram Pai <linuxram@...ibm.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, 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.

Thanks,
-Toshi


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