linux-kernel - Re: DISCONTIGMEM is deprecated

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Message-ID: <20190428081353.GB30901@infradead.org>
Date:   Sun, 28 Apr 2019 01:13:53 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Meelis Roos <mroos@...ux.ee>
Cc:     Christopher Lameter <cl@...ux.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mikulas Patocka <mpatocka@...hat.com>,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        linux-parisc@...r.kernel.org, linux-mm@...ck.org,
        Vlastimil Babka <vbabka@...e.cz>,
        LKML <linux-kernel@...r.kernel.org>, linux-arch@...r.kernel.org,
        Tony Luck <tony.luck@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>, linux-ia64@...r.kernel.org
Subject: Re: DISCONTIGMEM is deprecated

On Tue, Apr 23, 2019 at 07:49:57PM +0300, Meelis Roos wrote:
> > > ia64 (looks complicated ...)
> > 
> > Well as far as I can tell it was not even used 12 or so years ago on
> > Itanium when I worked on that stuff.
> 
> My notes tell that on UP ia64 (RX2620), !NUMA was broken with both
> SPARSEMEM and DISCONTIGMEM. NUMA+SPARSEMEM or !NUMA worked. Even
> NUMA+DISCONTIGMEM worked, that was my config on 2-CPU RX2660.

ia64 has a such a huge number of memory model choices.  Maybe we
need to cut it down to a small set that actually work.

That includes fund bits like the 'VIRTUAL_MEM_MAP' option where the
comment claims:

# VIRTUAL_MEM_MAP and FLAT_NODE_MEM_MAP are functionally equivalent.
# VIRTUAL_MEM_MAP has been retained for historical reasons.

but it still is selected as the default if sparsemem is not enabled..