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

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Date:	Thu, 20 Feb 2014 18:38:54 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Luiz Capitulino <lcapitulino@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andi Kleen <andi@...stfloor.org>,
	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 Wed, Feb 19, 2014 at 07:46:41PM -0800, David Rientjes wrote:
> On Wed, 19 Feb 2014, Marcelo Tosatti wrote:
> 
> > We agree that, in the future, we'd like to provide the ability to
> > dynamically allocate and free 1GB pages at runtime.
> > 
> > Extending the kernel command line interface is a first step.
> > 
> > Do you have a concrete objection to that first step ?
> > 
> 
> Yes, my concrete objection is that the command line interface is 
> unnecessary if you can dynamically allocate and free 1GB pages at runtime 
> unless memory will be so fragmented that it cannot be done when userspace 
> is brought up.  That is not your use case, thus this support is not 
> needed.  I think Mel also brought up this point.
> 
> There's no "first step" about it, this is unnecessary for your use case if 
> you can do it at runtime.  I'm not sure what's so surprising about this.
> 
> > > You can't specify an interleave behavior with Luiz's command line 
> > > interface so now we'd have two different interfaces for allocating 
> > > hugepage sizes depending on whether you're specifying a node or not.  
> > > It's "hugepagesz=1G hugepages=16" vs "hugepage_node=1:16:1G" (and I'd have 
> > > to look at previous messages in this thread to see if that means 16 1GB 
> > > pages on node 1 or 1 1GB pages on node 16.)
> > 
> > What syntax do you prefer and why ?
> > 
> 
> I'm not sure it's interesting to talk about since this patchset is 
> unnecessary if you can do it at runtime, but since "hugepagesz=" and 
> "hugepages=" have existed for many kernel releases, we must maintain 
> backwards compatibility.  Thus, it seems, the easiest addition would have 
> been "hugepagesnode=" which I've mentioned several times, there's no 
> reason to implement yet another command line option purely as a shorthand 
> which hugepage_node=1:2:1G is and in a very cryptic way.

There is one point from Davidlohr Bueso in favour of the proposed
command line interface. Did you consider that aspect?

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