linux-kernel - Re: [PATCH 2/3] mm, bootmem: panic in bootmem alloc functions even if slab is available

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Message-ID: <CAOJsxLH4RzWdxdVXyn+eFc56JfJtije2jK1eWaBYVaoZSHuUBA@mail.gmail.com>
Date:	Fri, 28 Dec 2012 00:27:11 +0200
From:	Pekka Enberg <penberg@...nel.org>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Sasha Levin <sasha.levin@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	"David S. Miller" <davem@...emloft.net>, Tejun Heo <tj@...nel.org>,
	Joonsoo Kim <js1304@...il.com>,
	Yinghai Lu <yinghai@...nel.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] mm, bootmem: panic in bootmem alloc functions even if
 slab is available

On Sun, 23 Dec 2012, Sasha Levin wrote:
>> diff --git a/mm/bootmem.c b/mm/bootmem.c
>> index 1324cd7..198a92f 100644
>> --- a/mm/bootmem.c
>> +++ b/mm/bootmem.c
>> @@ -763,9 +763,6 @@ void * __init ___alloc_bootmem_node(pg_data_t *pgdat, unsigned long size,
>>  void * __init __alloc_bootmem_node(pg_data_t *pgdat, unsigned long size,
>>                                  unsigned long align, unsigned long goal)
>>  {
>> -     if (WARN_ON_ONCE(slab_is_available()))
>> -             return kzalloc_node(size, GFP_NOWAIT, pgdat->node_id);
>> -
>>       return  ___alloc_bootmem_node(pgdat, size, align, goal, 0);
>>  }

On Fri, Dec 28, 2012 at 12:25 AM, David Rientjes <rientjes@...gle.com> wrote:
> All you're doing is removing the fallback if this happens to be called
> with slab_is_available().  It's still possible that the slab allocator can
> successfully allocate the memory, though.  So it would be rather
> unfortunate to start panicking in a situation that used to only emit a
> warning.
>
> Why can't you panic only kzalloc_node() returns NULL and otherwise just
> return the allocated memory?

I'm not sure what Sasha's patch is trying to do here but the fall-back
is there simply to let the caller know it's calling the bootmem
allocator *too late*. That is, the slab allocator is already up and
running so you're expected to use that.

                        Pekka
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