linux-kernel - Re: bootmem allocator

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Message-ID: <47FBAF13.6000007@zytor.com>
Date:	Tue, 08 Apr 2008 10:44:51 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Ingo Molnar <mingo@...e.hu>, Cyrill Gorcunov <gorcunov@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Yinghai Lu <yhlu.kernel@...il.com>
Subject: Re: bootmem allocator

Andi Kleen wrote:
> On Tue, Apr 08, 2008 at 10:04:46AM +0200, Ingo Molnar wrote:
>> * Andi Kleen <andi@...stfloor.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 
> 
> I was considering that too, but we have so many weird variants of bootmem
> with opt in and opt out and even combinations of both now that the whole thing 
> is starting to look really pear shaped (I admit I added some of them
> in the past myself but I'm not proud). Would be a great project for
> someone to consolidate that all a bit.
> 

True, but if the gbpages hugetlbfs case is the *only* case which wants a 
nonclearing interface (which it sounds like it is), then it seems like a 
really bad idea to change the default.

hugetlbfs is a pretty special case.

	-hpa
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