linux-kernel - Re: [PATCH v5 2/3] iommu/io-pgtable-arm-v7s: Request DMA32 memory, and improve debugging

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Message-ID: <20181207080551.GA15120@bombadil.infradead.org>
Date:   Fri, 7 Dec 2018 00:05:51 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Nicolas Boichat <drinkcat@...omium.org>
Cc:     Will Deacon <will.deacon@....com>,
        Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...e.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Levin Alexander <Alexander.Levin@...rosoft.com>,
        Huaisheng Ye <yehs1@...ovo.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        linux-arm-kernel@...ts.infradead.org,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Yong Wu <yong.wu@...iatek.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Tomasz Figa <tfiga@...gle.com>, yingjoe.chen@...iatek.com,
        hch@...radead.org
Subject: Re: [PATCH v5 2/3] iommu/io-pgtable-arm-v7s: Request DMA32 memory,
 and improve debugging

On Fri, Dec 07, 2018 at 02:16:19PM +0800, Nicolas Boichat wrote:
> +#ifdef CONFIG_ZONE_DMA32
> +#define ARM_V7S_TABLE_GFP_DMA GFP_DMA32
> +#define ARM_V7S_TABLE_SLAB_CACHE SLAB_CACHE_DMA32

This name doesn't make any sense.  Why not ARM_V7S_TABLE_SLAB_FLAGS ?

> +#else
> +#define ARM_V7S_TABLE_GFP_DMA GFP_DMA
> +#define ARM_V7S_TABLE_SLAB_CACHE SLAB_CACHE_DMA

Can you remind me again why it is, on machines which don't support
ZONE_DMA32, why we have to allocate from ZONE_DMA?  My understanding
is that 64-bit machines have ZONE_DMA32 and 32-bit machines don't.
So shouldn't this rather be GFP_KERNEL?

Actually, maybe we could centralise this in gfp.h:

#ifdef CONFIG_64BIT
# ifdef CONFIG_ZONE_DMA32
#define GFP_32BIT	GFP_DMA32
# else
#define GFP_32BIT	GFP_DMA
#else /* 32-bit */
#define GFP_32BIT	GFP_KERNEL
#endif