linux-kernel - Re: [PATCH 4/4] hugetlb: add hugepages

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Date:	Fri, 21 Feb 2014 14:44:05 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Andi Kleen <andi@...stfloor.org>
cc:	Marcelo Tosatti <mtosatti@...hat.com>,
	Luiz Capitulino <lcapitulino@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Rik van Riel <riel@...hat.com>, davidlohr@...com,
	isimatu.yasuaki@...fujitsu.com, yinghai@...nel.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 4/4] hugetlb: add hugepages_node= command-line option

On Fri, 21 Feb 2014, Andi Kleen wrote:

> > > 2) it improves the kernel command line interface from incomplete
> > > (lacking the ability to specify node<->page correlation), to 
> > > a complete interface.
> > > 
> > 
> > If GB hugepages can be allocated dynamically, I really think we should be 
> > able to remove hugepagesz= entirely for x86 after a few years of 
> > supporting it for backwards compatibility, even though Linus has insisted 
> 
> That doesn't make any sense. Why break a perfectly fine interface?
> 

I think doing hugepagesz= and not default_hugepagesz= is more of a hack 
just because we lack support for dynamically allocating some class of 
hugepage sizes and this is the only way to currently do it; if we had 
support for doing it at runtime then that hack probably isn't needed.  You 
would still be able to do default_hugepagesz=1G and allocate a ton of them 
when fragmentation is a concern and it can only truly be done at boot.  
Even then, with such a large size it doesn't seem absolutely necessary 
since you'd either be (a) oom as a result of all those hugepages or (b) 
there would be enough memory for initscripts to do this at runtime, this 
isn't the case with 2MB.

But, like I said, I'm not sure we'd ever be able to totally remove it 
because of backwards compatibility, but the point is that nobody would 
have to use it anymore as a hack for 1GB.
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