linux-kernel - Re: DISCONTIGMEM is deprecated

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Message-ID: <20190428081107.GA30901@infradead.org>
Date:   Sun, 28 Apr 2019 01:11:07 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Mike Rapoport <rppt@...ux.ibm.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Matthew Wilcox <willy@...radead.org>,
        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
Subject: Re: DISCONTIGMEM is deprecated

On Wed, Apr 24, 2019 at 02:33:53PM +0300, Mike Rapoport wrote:
> On Tue, Apr 23, 2019 at 12:13:54AM -0700, Christoph Hellwig wrote:
> > On Sun, Apr 21, 2019 at 10:16:04PM +0100, Mel Gorman wrote:
> > > 32-bit NUMA systems should be non-existent in practice. The last NUMA
> > > system I'm aware of that was both NUMA and 32-bit only died somewhere
> > > between 2004 and 2007. If someone is running a 64-bit capable system in
> > > 32-bit mode with NUMA, they really are just punishing themselves for fun.
> > 
> > Can we mark it as BROKEN to see if someone shouts and then remove it
> > a year or two down the road?  Or just kill it off now..
> 
> How about making SPARSEMEM default for x86-32?

Sounds good.

Another question:  I always found the option to even select the memory
models like a bad tradeoff.  Can we really expect a user to make a sane
choice?  I'd rather stick to a relativelty optimal choice based on arch
and maybe a few other parameters (NUMA or not for example) and stick to
it, reducing the testing matrix.