linux-kernel - Re: [PATCH] mm: make free_bootmem to loop bdata

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Message-Id: <20080314110451.b41712b4.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Fri, 14 Mar 2008 11:04:51 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	"Yinghai Lu" <yhlu.kernel@...il.com>
Cc:	"Andrew Morton" <akpm@...ux-foundation.org>, mingo@...e.hu,
	clameter@....com, linux-kernel@...r.kernel.org,
	"Andi Kleen" <ak@...e.de>, "Yasunori Goto" <y-goto@...fujitsu.com>
Subject: Re: [PATCH] mm: make free_bootmem to loop bdata_list

On Thu, 13 Mar 2008 18:39:34 -0700
"Yinghai Lu" <yhlu.kernel@...il.com> wrote:

> On Thu, Mar 13, 2008 at 6:39 PM, KAMEZAWA Hiroyuki
> <kamezawa.hiroyu@...fujitsu.com> wrote:
> > On Thu, 13 Mar 2008 11:53:31 -0700
> >  "Yinghai Lu" <yhlu.kernel@...il.com> wrote:
> >  > ===================================================================
> >  > --- linux-2.6.orig/mm/bootmem.c
> >  > +++ linux-2.6/mm/bootmem.c
> >  > @@ -427,7 +438,9 @@ int __init reserve_bootmem(unsigned long
> >  >
> >  >  void __init free_bootmem(unsigned long addr, unsigned long size)
> >  >  {
> >  > -     free_bootmem_core(NODE_DATA(0)->bdata, addr, size);
> >  > +     bootmem_data_t *bdata;
> >  > +     list_for_each_entry(bdata, &bdata_list, list)
> >  > +             free_bootmem_core(bdata, addr, size);
> >  >  }
> >
> >
> >  Just a confirmation.
> >  In above loop, boundary check in free_bootmem_core() hits two or more times ?
> >  If yes, it's ok.
> >  If no, please exit loop at hit.
> 
> yes. need that handle range cross node (RAMDISK case that is end
> beyond end_of_ram).
> 
Then, <addr, size> can spread across nodes. 

IMHO, there are *big* memory hole between nodes in some systems. 
This kind of interface, which allows alloc/free bootmem accross nodes,
will see terrible trouble when a programmer assumes  "alloc/free bootmem
always return contiguous size of memory" (This is guaranteed now,)

Does the new allocator (you changed ?) guarantee that returned <address, size>
is fully contiguous even if it spreads accross nodes ?

If no, NACK for this version.

Thanks,
-Kame


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