linux-kernel - Re: [External] Re: [RFC PATCH v2 00/12] get rid of GFP_ZONE

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Date:   Wed, 30 May 2018 11:11:19 +0200
From:   Christoph Hellwig <hch@....de>
To:     Huaisheng HS1 Ye <yehs1@...ovo.com>
Cc:     Michal Hocko <mhocko@...nel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "willy@...radead.org" <willy@...radead.org>,
        "vbabka@...e.cz" <vbabka@...e.cz>,
        "mgorman@...hsingularity.net" <mgorman@...hsingularity.net>,
        "kstewart@...uxfoundation.org" <kstewart@...uxfoundation.org>,
        "alexander.levin@...izon.com" <alexander.levin@...izon.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "colyli@...e.de" <colyli@...e.de>,
        NingTing Cheng <chengnt@...ovo.com>,
        Ocean HY1 He <hehy1@...ovo.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        "linux-btrfs@...r.kernel.org" <linux-btrfs@...r.kernel.org>,
        Christoph Hellwig <hch@....de>
Subject: Re: [External]  Re: [RFC PATCH v2 00/12] get rid of
        GFP_ZONE_TABLE/BAD

On Wed, May 30, 2018 at 09:02:13AM +0000, Huaisheng HS1 Ye wrote:
> 
> I don't quite understand that. I think those, mostly drivers, need to
> get the correct zone they want. ZONE_DMA32 is an example, if drivers can be
> satisfied with a low mem zone, why they mark the gfp flags as
> 'GFP_KERNEL|__GFP_DMA32'?

Drivers should never use GFP_DMA32 directly.  The right abstraction is
the DMA API, ZONE_DMA32 is just a helper.