linux-kernel - Re: [PATCH] mm: nobootmem: Correct alloc

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Message-Id: <20120503.130416.839732919427673590.davem@davemloft.net>
Date:	Thu, 03 May 2012 13:04:16 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	hannes@...xchg.org
Cc:	yinghai@...nel.org, linux-kernel@...r.kernel.org, tj@...nel.org,
	torvalds@...ux-foundation.org
Subject: Re: [PATCH] mm: nobootmem: Correct alloc_bootmem semantics.

From: Johannes Weiner <hannes@...xchg.org>
Date: Thu, 3 May 2012 17:28:41 +0200

> On Wed, Apr 25, 2012 at 07:00:34PM -0400, David Miller wrote:
>> From: Yinghai Lu <yinghai@...nel.org>
>> Date: Wed, 25 Apr 2012 15:46:42 -0700
>> 
>> > On Wed, Apr 25, 2012 at 1:10 PM, David Miller <davem@...emloft.net> wrote:
>> >> @@ -298,13 +298,19 @@ void * __init __alloc_bootmem_node(pg_data_t *pgdat, unsigned long size,
>> >>        if (WARN_ON_ONCE(slab_is_available()))
>> >>                return kzalloc_node(size, GFP_NOWAIT, pgdat->node_id);
>> >>
>> >> +again:
>> >>        ptr = __alloc_memory_core_early(pgdat->node_id, size, align,
>> >>                                         goal, -1ULL);
>> >>        if (ptr)
>> >>                return ptr;
>> > 
>> > If you want to be consistent to bootmem version.
>> > 
>> > again label should be here instead.
>> 
>> It is merely an artifact of implementation that the bootmem version
>> doesn't try to respect the given node if the goal cannot be satisfied,
>> and in fact I would classify that as a bug that needs to be fixed.
>> 
>> Therefore, I believe the bootmem case is what needs to be adjusted
>> instead.
> 
> Now it does: node+goal, goal, node, anywhere
> 
> whereas the memblock version of __alloc_bootmem_node_nopanic() also
> still does: node+goal, goal, anywhere
> 
> Your description suggests that the node should be higher prioritized
> than the goal, which I understand as: node+goal, node, anywhere.
> 
> Which do we actually want?

I think the goal is what needs to be prioritized.  An explicit goal usually
has a requirement, like "I need physical memory in the low 32-bits" and if
they specified an explicit node they really mean "and give me it on NUMA
node X if you can."  Hence the sequence:

	node+goal, goal, node, any

the only other reasonable option would be:

	node+goal, node, goal, any

but I think that doesn't match what people want when an explicit goal
is specified.  Do you?
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