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From: Tejun Heo <tj@kernel.org>
To: Cyril Chemparathy <cyril@ti.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	akpm@linux-foundation.org, davem@davemloft.net,
	eric.dumazet@gmail.com, hannes@cmpxchg.org,
	shangw@linux.vnet.ibm.com, vitalya@ti.com
Subject: Re: [PATCH] mm: bootmem: use phys_addr_t for physical addresses
Date: Wed, 12 Sep 2012 17:34:00 -0700	[thread overview]
Message-ID: <20120913003400.GA25889@localhost> (raw)
In-Reply-To: <505123FE.2090305@ti.com>

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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WARNING: multiple messages have this Message-ID (diff)
From: Tejun Heo <tj@kernel.org>
To: Cyril Chemparathy <cyril@ti.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	akpm@linux-foundation.org, davem@davemloft.net,
	eric.dumazet@gmail.com, hannes@cmpxchg.org,
	shangw@linux.vnet.ibm.com, vitalya@ti.com
Subject: Re: [PATCH] mm: bootmem: use phys_addr_t for physical addresses
Date: Wed, 12 Sep 2012 17:34:00 -0700	[thread overview]
Message-ID: <20120913003400.GA25889@localhost> (raw)
In-Reply-To: <505123FE.2090305@ti.com>

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

  reply	other threads:[~2012-09-13  0:34 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-09-12 16:06 [PATCH] mm: bootmem: use phys_addr_t for physical addresses Cyril Chemparathy
2012-09-12 16:06 ` Cyril Chemparathy
2012-09-12 20:39 ` Tejun Heo
2012-09-12 20:39   ` Tejun Heo
2012-09-13  0:08   ` Cyril Chemparathy
2012-09-13  0:08     ` Cyril Chemparathy
2012-09-13  0:34     ` Tejun Heo [this message]
2012-09-13  0:34       ` Tejun Heo
2012-09-13  0:40       ` Cyril Chemparathy
2012-09-13  0:40         ` Cyril Chemparathy
2012-09-13 19:32         ` Tejun Heo
2012-09-13 19:32           ` Tejun Heo

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