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Message-ID: <1392702456.2468.4.camel@buesod1.americas.hpqcorp.net>
Date: Mon, 17 Feb 2014 21:47:36 -0800
From: Davidlohr Bueso <davidlohr@...com>
To: David Rientjes <rientjes@...gle.com>
Cc: Luiz Capitulino <lcapitulino@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>, mtosatti@...hat.com,
Mel Gorman <mgorman@...e.de>,
Andrea Arcangeli <aarcange@...hat.com>,
Andi Kleen <andi@...stfloor.org>,
Rik van Riel <riel@...hat.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 Sat, 2014-02-15 at 02:06 -0800, David Rientjes wrote:
> On Fri, 14 Feb 2014, Luiz Capitulino wrote:
>
> > > 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=<#>
> >
> > That was my first try but it turned out really bad. First, for every node
> > you specify you need three options.
>
> Just like you need two options today to specify a number of hugepages of a
> particular non-default size. You only need to use hugepagesz= or
> hugepagenode= if you want a non-default size or a specify a particular
> node.
>
> > So, if you want to setup memory for
> > three nodes you'll need to specify nine options.
>
> And you currently need six if you want to specify three different hugepage
> sizes (?). But who really specifies three different hugepage sizes on the
> command line that are needed to be reserved at boot?
>
> If that's really the usecase, it seems like you want the old
> CONFIG_PAGE_SHIFT patch.
>
> > And it gets worse, because
> > hugepagesz= and hugepages= have strict ordering (which is a mistake, IMHO) so
> > you have to specify them in the right order otherwise things don't work as
> > expected and you have no idea why (have been there myself).
> >
>
> How is that difficult? hugepages= is the "noun", hugepagesz= is the
> "adjective". hugepages=100 hugepagesz=1G hugepages=4 makes perfect sense
> to me, and I actually don't allocate hugepages on the command line, nor
> have I looked at Documentation/kernel-parameters.txt to check if I'm
> constructing it correctly. It just makes sense and once you learn it it's
> just natural.
This can get annoying _really_ fast for larger systems.
> > IMO, hugepages_node=<nid>:<nr_pages>:<size>,... is good enough. It's concise,
> > and don't depend on any other option to function. Also, there are lots of other
> > kernel command-line options that require you to specify multiple fields, so
> > it's not like hugepages_node= is totally different in that regard.
> >
Agreed.
>
> I doubt Andrew is going to want a completely different format for hugepage
> allocations that want to specify a node and have to deal with people who
> say hugepages_node=2:1:1G and constantly have to lookup if it's 2
> hugepages on node 1 or 1 hugepage on node 2.
I guess most users won't even be aware of this new parameter and those
who really care will have the choice.
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