linux-kernel - Re: [LSF/MM TOPIC NOTES] x86 ZONE

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Message-ID: <20180503121322.GA14864@infradead.org>
Date:   Thu, 3 May 2018 05:13:22 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Matthew Wilcox <willy6545@...il.com>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Christoph Hellwig <hch@...radead.org>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Julia Lawall <julia.lawall@...6.fr>, linux-mm@...ck.org,
        cl@...ux.com, Jan Kara <jack@...e.cz>, matthew@....cx,
        x86@...nel.org, luto@...capital.net, martin.petersen@...cle.com,
        jthumshirn@...e.de, broonie@...nel.org,
        Juergen Gross <jgross@...e.com>, linux-spi@...r.kernel.org,
        Joerg Roedel <joro@...tes.org>, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        "lsf-pc@...ts.linux-foundation.org" 
        <lsf-pc@...ts.linux-foundation.org>
Subject: Re: [LSF/MM TOPIC NOTES] x86 ZONE_DMA love

On Thu, May 03, 2018 at 02:03:38PM +0200, Michal Hocko wrote:
> On Sat 28-04-18 19:10:47, Matthew Wilcox wrote:
> > Another way we could approach this is to get rid of ZONE_DMA. Make GFP_DMA
> > a flag which doesn't map to a zone. Rather, it redirects to a separate
> > allocator. At boot, we hand all memory under 16MB to the DMA allocator. The
> > DMA allocator can have a shrinker which just hands back all the memory once
> > we're under memory pressure (if it's never had an allocation).
> 
> Yeah, that was exactly the plan with the CMA allocator... We wouldn't
> need the shrinker because who cares about 16MB which is not usable
> anyway.

The CMA pool sounds fine.  But please kill GFP_DMA off first / at the
same time.  95% of the users are either completely bogus or should be
using the DMA API, and the few other can use the new allocator directly.