linux-kernel - Re: [PATCH 18/39] lmb: Add lmb_reserve_area_overlap

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Message-ID: <4BC40336.4030902@oracle.com>
Date:	Mon, 12 Apr 2010 22:37:58 -0700
From:	Yinghai <yinghai.lu@...cle.com>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
CC:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Miller <davem@...emloft.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH 18/39] lmb: Add lmb_reserve_area_overlap_ok()

On 04/12/2010 10:10 PM, Benjamin Herrenschmidt wrote:
> On Mon, 2010-04-12 at 21:44 -0700, Yinghai wrote:
> 
>> that is only for some special cases about area that is reserved for fw region.
> 
> And ? From what I can see in the code, it will still not work properly
> unless all your special cases end up fitting right with the bug you
> effectively have..

not sure.

noticed there some overlapped, and with this patch, those overlapped area disappeared

> 
>> and even there is overlapped area, it the code still can go through when lmb_to_bootmem or create range list for slab.
>> because they are using range array subtract.
> 
> Well, either we just have overlapped areas or we don't ... we shouldn't
> have some kind of overlap_ok() thing that does the right thing ..
> sometimes, but maybe not, but we don't care anyways, which is what you
> seem to be saying.
yes.
> 
>>> Besides, lmb_reserve_area_overlap_ok() sucks as a name :-)
>>
>> any suggestion for better name?
> 
> Well, what you actually implemented is 
> 
> lmb_reserve_area_overlap_maybe_ok_not_too_sure_though()
> 
> What we should decide is once for all, is it ok to have lmb_reserve() be
> called for overlapping ranges. I think the answer is yes and in fact, we
> don't take special care in powerpc either there so overlap could happen
> in theory.
> 
> Now, do we want to avoid actually creating overlapping regions in the
> array ? I think we should look into it, but then we should fix
> lmb_reserve() to do the right thing here and coalesce all the overlaps.

not sure if is needed. lmb_free/lmb_reserve seems work.

YH
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