linux-kernel - Re: [PATCH 0/4] hugetlb: add hugepagesnid= command-line option

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Message-ID: <20140211152629.GA28210@amt.cnet>
Date:	Tue, 11 Feb 2014 13:26:29 -0200
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Mel Gorman <mgorman@...e.de>
Cc:	David Rientjes <rientjes@...gle.com>,
	Luiz Capitulino <lcapitulino@...hat.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andi Kleen <andi@...stfloor.org>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH 0/4] hugetlb: add hugepagesnid= command-line option

On Tue, Feb 11, 2014 at 09:25:14AM +0000, Mel Gorman wrote:
> On Mon, Feb 10, 2014 at 06:54:20PM -0800, David Rientjes wrote:
> > On Mon, 10 Feb 2014, Luiz Capitulino wrote:
> > 
> > > HugeTLB command-line option hugepages= allows the user to specify how many
> > > huge pages should be allocated at boot. On NUMA systems, this argument
> > > automatically distributes huge pages allocation among nodes, which can
> > > be undesirable.
> > > 
> > 
> > And when hugepages can no longer be allocated on a node because it is too 
> > small, the remaining hugepages are distributed over nodes with memory 
> > available, correct?
> > 
> > > The hugepagesnid= option introduced by this commit allows the user
> > > to specify which NUMA nodes should be used to allocate boot-time HugeTLB
> > > pages. For example, hugepagesnid=0,2,2G will allocate two 2G huge pages
> > > from node 0 only. More details on patch 3/4 and patch 4/4.
> > > 
> > 
> > Strange, it would seem better to just reserve as many hugepages as you 
> > want so that you get the desired number on each node and then free the 
> > ones you don't need at runtime.

You have to know the behaviour of the allocator, and rely on that 
to allocate the exact number of 1G hugepages on a particular node.

Is that desired in constrast with specifying the exact number, and
location, of hugepages to allocated?

> Or take a stab at allocating 1G pages at runtime. It would require
> finding properly aligned 1Gs worth of contiguous MAX_ORDER_NR_PAGES at
> runtime. I would expect it would only work very early in the lifetime of
> the system but if the user is willing to use kernel parameters to
> allocate them then it should not be an issue.

Can be an improvement on top of the current patchset? Certain use-cases
require allocation guarantees (even if that requires kernel parameters).

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