linux-kernel - Re: mmotm boot panic bootmem-avoid-dma32-zone-by-default.patch

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Message-ID: <4B91B4EF.5090502@kernel.org>
Date:	Fri, 05 Mar 2010 17:50:39 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Johannes Weiner <hannes@...xchg.org>
CC:	Greg Thelen <gthelen@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, linux-mm@...ck.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: mmotm boot panic bootmem-avoid-dma32-zone-by-default.patch

On 03/05/2010 03:58 PM, Johannes Weiner wrote:
> Hello Yinghai,
> 
> On Fri, Mar 05, 2010 at 10:41:56AM -0800, Yinghai Lu wrote:
>> On 03/04/2010 09:17 PM, Greg Thelen wrote:
>>> On Thu, Mar 4, 2010 at 7:21 PM, Johannes Weiner <hannes@...xchg.org> wrote:
>>>> On Thu, Mar 04, 2010 at 01:21:41PM -0800, Greg Thelen wrote:
>>>>> On several systems I am seeing a boot panic if I use mmotm
>>>>> (stamp-2010-03-02-18-38).  If I remove
>>>>> bootmem-avoid-dma32-zone-by-default.patch then no panic is seen.  I
>>>>> find that:
>>>>> * 2.6.33 boots fine.
>>>>> * 2.6.33 + mmotm w/o bootmem-avoid-dma32-zone-by-default.patch: boots fine.
>>>>> * 2.6.33 + mmotm (including
>>>>> bootmem-avoid-dma32-zone-by-default.patch): panics.
>> ...
>>>
>>> Note: mmotm has been recently updated to stamp-2010-03-04-18-05.  I
>>> re-tested with 'make defconfig' to confirm the panic with this later
>>> mmotm.
>>
>> please check
>>
>> [PATCH] early_res: double check with updated goal in alloc_memory_core_early
>>
>> Johannes Weiner pointed out that new early_res replacement for alloc_bootmem_node
>> change the behavoir about goal.
>> original bootmem one will try go further regardless of goal.
>>
>> and it will break his patch about default goal from MAX_DMA to MAX_DMA32...
>> also broke uncommon machines with <=16M of memory.
>> (really? our x86 kernel still can run on 16M system?)
>>
>> so try again with update goal.
> 
> Thanks for the patch, it seems to be correct.
> 
> However, I have a more generic question about it, regarding the future of the
> early_res allocator.
> 
> Did you plan on keeping the bootmem API for longer?  Because my impression was,
> emulating it is a temporary measure until all users are gone and bootmem can
> be finally dropped.

that depends on every arch maintainer.

user can compare them on x86 to check if...

next step will be make fw_mem_map to generiaized and combine them with lmb.

> 
> But then this would require some sort of handling of 'user does not need DMA[32]
> memory, so avoid it' and 'user can only use DMA[32] memory' in the early_res
> allocator as well.
> 
> I ask this specifically because you move this fix into the bootmem compatibility
> code while there is not yet a way to tell early_res the same thing, so switching
> a user that _needs_ to specify this requirement from bootmem to early_res is not
> yet possible, is it?

just let caller set the goal.

> 
>> Reported-by: Greg Thelen <gthelen@...gle.com>
>> Signed-off-by: Yinghai Lu <yinghai@...nel.org>
>>
>> ---
>>  mm/bootmem.c |   28 +++++++++++++++++++++++++---
>>  1 file changed, 25 insertions(+), 3 deletions(-)
>>
>> Index: linux-2.6/mm/bootmem.c
>> ===================================================================
>> --- linux-2.6.orig/mm/bootmem.c
>> +++ linux-2.6/mm/bootmem.c
>> @@ -170,6 +170,28 @@ void __init free_bootmem_late(unsigned l
>>  }
>>  
>>  #ifdef CONFIG_NO_BOOTMEM
>> +static void * __init ___alloc_memory_core_early(pg_data_t *pgdat, u64 size,
>> +						 u64 align, u64 goal, u64 limit)
>> +{
>> +	void *ptr;
>> +	unsigned long end_pfn;
>> +
>> +	ptr = __alloc_memory_core_early(pgdat->node_id, size, align,
>> +					 goal, limit);
>> +	if (ptr)
>> +		return ptr;
>> +
>> +	/* check goal according  */
>> +	end_pfn = pgdat->node_start_pfn + pgdat->node_spanned_pages;
>> +	if ((end_pfn << PAGE_SHIFT) < (goal + size)) {
>> +		goal = pgdat->node_start_pfn << PAGE_SHIFT;
>> +		ptr = __alloc_memory_core_early(pgdat->node_id, size, align,
>> +						 goal, limit);
>> +	}
>> +
>> +	return ptr;
> 
> I think it would make sense to move the parameter check before doing the
> allocation.  Then you save the second call.

I am trying to avoid the second call.
please check another patch about "introduce bootmem_default_goal : don't punish 64bit system without 4g ram"

> 
> And a second nitpick: naming the inner function __foo and the outer one ___foo seems
> confusing to me.  Could you maybe rename the wrapper? bootmem_compat_alloc_early() or
> something like that?

ok.

Thanks

Yinghai
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