linux-kernel - Re: [PATCH] mm: bootmem: use phys_addr

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Date:	Wed, 12 Sep 2012 17:34:00 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Cyril Chemparathy <cyril@...com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	akpm@...ux-foundation.org, davem@...emloft.net,
	eric.dumazet@...il.com, hannes@...xchg.org,
	shangw@...ux.vnet.ibm.com, vitalya@...com
Subject: Re: [PATCH] mm: bootmem: use phys_addr_t for physical addresses

Hello,

On Wed, Sep 12, 2012 at 08:08:30PM -0400, Cyril Chemparathy wrote:
> >So, a function which takes phys_addr_t for goal and limit but returns
> >void * doesn't make much sense unless the function creates directly
> >addressable mapping somewhere.
> 
> On the 32-bit PAE platform in question, physical memory is located
> outside the 4GB range.  Therefore phys_to_virt takes a 64-bit
> physical address and returns a 32-bit kernel mapped lowmem pointer.

Yes but phys_to_virt() can return the vaddr only if the physical
address is already mapped in the kernel address space; otherwise, you
need one of the kmap*() calls which may not be online early in the
boot and consumes either the vmalloc area or fixmaps.  bootmem
interface can't handle unmapped memory.

Thanks.

-- 
tejun
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