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Date: Tue, 08 Apr 2008 23:00:28 -0700
From: Mike Travis <travis@sgi.com>
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To: Ingo Molnar <mingo@elte.hu>
CC: Andi Kleen <andi@firstfloor.org>, Cyrill Gorcunov <gorcunov@gmail.com>,
       "H. Peter Anvin" <hpa@zytor.com>, LKML <linux-kernel@vger.kernel.org>,
       Yinghai Lu <yhlu.kernel@gmail.com>, Eric Dumazet <dada1@cosmosbay.com>
Subject: Re: bootmem allocator
References: <20080407185613.GD9211@cvg> <20080407190904.GH12292@elte.hu> <87iqytqwl7.fsf@basil.nowhere.org> <20080408080446.GA12308@elte.hu>
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Ingo Molnar wrote:
> * Andi Kleen <andi@firstfloor.org> wrote:
> 
>>> hm, bootmem allocator is supposed to clear memory. We have a couple 
>>> of places that rely on that.
>> I was actually considering to change that for the GB pages hugetlbfs 
>> patchkit, because memset for 1G is a little slow and not needed (will 
>> be cleared later anyways) and it might be a problem for very large 
>> systems with a lot of such pages at boot.
> 
> changing the default behavior of bootmem alloc to be non-clearing is a 
> really bad idea that will only cause unrobustness. The proper approach 
> is to add an _opt-in_ API that does not clear memory 
> (bootmem_alloc_dontclear() or whatever), available to callers that know 
> it for sure that they dont need the clearing.

Yes, changing the default of bootmem_alloc is a bad idea.  I just changed
a bunch of static arrays to bootmem alloc's and it was pointed out early
that not only does bootmem_alloc clear memory, but also panics if it's not
available.

> Also take into account that alloc_bootmem_low() :
> - calls panic() if not enough memory
> - already clears allocated memory
> Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>

A specialized call to bootmem_alloc probably needs it's own API... ;-)

Thanks,
Mike