linux-kernel - Re: [PATCH v2 0/3] iommu/io-pgtable-arm-v7s: Use DMA32 zone for page tables

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Message-ID: <20181123123040.GH8625@dhcp22.suse.cz>
Date:   Fri, 23 Nov 2018 13:30:40 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Robin Murphy <robin.murphy@....com>,
        Matthew Wilcox <willy@...radead.org>,
        Christopher Lameter <cl@...ux.com>,
        Levin Alexander <Alexander.Levin@...rosoft.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Nicolas Boichat <drinkcat@...omium.org>,
        Huaisheng Ye <yehs1@...ovo.com>,
        Tomasz Figa <tfiga@...gle.com>,
        Will Deacon <will.deacon@....com>,
        linux-kernel@...r.kernel.org, Pekka Enberg <penberg@...nel.org>,
        linux-mm@...ck.org, iommu@...ts.linux-foundation.org,
        linux-arm-kernel@...ts.infradead.org,
        David Rientjes <rientjes@...gle.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        yingjoe.chen@...iatek.com, Joonsoo Kim <iamjoonsoo.kim@....com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2 0/3] iommu/io-pgtable-arm-v7s: Use DMA32 zone for page
 tables

On Fri 23-11-18 13:23:41, Vlastimil Babka wrote:
> On 11/22/18 9:23 AM, Christoph Hellwig wrote:
[...]
> > But I do agree with the sentiment of not wanting to spread GFP_DMA32
> > futher into the slab allocator.
> 
> I don't see a problem with GFP_DMA32 for custom caches. Generic
> kmalloc() would be worse, since it would have to create a new array of
> kmalloc caches. But that's already ruled out due to the alignment.

Yes that makes quite a lot of sense to me. We do not really need a
generic support. Just make sure that if somebody creates a GFP_DMA32
restricted cache then allow allocating restricted memory from that.

Is there any fundamental reason that this wouldn't be possible?
-- 
Michal Hocko
SUSE Labs