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

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Date:	Fri, 14 Feb 2014 15:14:22 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Luiz Capitulino <lcapitulino@...hat.com>
cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, mtosatti@...hat.com, mgorman@...e.de,
	aarcange@...hat.com, andi@...stfloor.org, riel@...hat.com,
	davidlohr@...com, isimatu.yasuaki@...fujitsu.com,
	yinghai@...nel.org
Subject: Re: [PATCH 4/4] hugetlb: add hugepages_node= command-line option

On Thu, 13 Feb 2014, Luiz Capitulino wrote:

> From: Luiz capitulino <lcapitulino@...hat.com>
> 
> The HugeTLB command-line option hugepages= allows a user to specify how
> many huge pages should be allocated at boot. This option is needed because
> it improves reliability when allocating 1G huge pages, which are better
> allocated as early as possible due to fragmentation.
> 
> However, hugepages= has a limitation. On NUMA systems, hugepages= will
> automatically distribute memory allocation equally among nodes. For
> example, if you have a 2-node NUMA system and allocate 200 huge pages,
> than hugepages= will try to allocate 100 huge pages from node0 and 100
> from node1.
> 
> This is very unflexible, as it doesn't allow you to specify which nodes
> the huge pages should be allocated from. For example, there are use-cases
> where the user wants to specify that a 1GB huge page should be allocated
> from node 2 or that 300 2MB huge pages should be allocated from node 0.
> 
> The hugepages_node= command-line option introduced by this commit allows
> just that.
> 
> The syntax is:
> 
>   hugepages_node=nid:nr_pages:size,...
> 

Again, I think this syntax is horrendous and doesn't couple well with the 
other hugepage-related kernel command line options.  We already have 
hugepages= and hugepagesz= which you can interleave on the command line to 
get 100 2M hugepages and 10 1GB hugepages, for example.

This patchset is simply introducing another variable to the matter: the 
node that the hugepages should be allocated on.  So just introduce a 
hugepagesnode= parameter to couple with the others so you can do

	hugepagesz=<size> hugepagesnode=<nid> hugepages=<#>

instead of having completely confusing interfaces where you want to do 
hugepages_node=1:1:1G for a 1GB hugepage on page 1 (and try remembering 
which "1" means what, yuck) and "hugepagesz=1GB hugepages=1" if you're 
indifferent to the node.
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