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From:   Nicolas Boichat <drinkcat@chromium.org>
Date:   Thu, 6 Dec 2018 18:09:39 +0800
Message-ID: <CANMq1KAJ7YvbpUvRqP0zEWY1_pC-TvHMZYn4FUj4A9Bpmv_jxg@mail.gmail.com>
Subject: Re: [PATCH v4 2/3] mm: Add support for kmem caches in DMA32 zone
To:     Vlastimil Babka <vbabka@suse.cz>
Cc:     Will Deacon <will.deacon@arm.com>,
        Robin Murphy <robin.murphy@arm.com>,
        Joerg Roedel <joro@8bytes.org>,
        Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Michal Hocko <mhocko@suse.com>,
        Mel Gorman <mgorman@techsingularity.net>,
        Levin Alexander <Alexander.Levin@microsoft.com>,
        Huaisheng Ye <yehs1@lenovo.com>,
        Mike Rapoport <rppt@linux.vnet.ibm.com>,
        linux-arm Mailing List <linux-arm-kernel@lists.infradead.org>,
        iommu@lists.linux-foundation.org,
        lkml <linux-kernel@vger.kernel.org>, linux-mm@kvack.org,
        Yong Wu <yong.wu@mediatek.com>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        Tomasz Figa <tfiga@google.com>, yingjoe.chen@mediatek.com,
        hch@infradead.org, Matthew Wilcox <willy@infradead.org>
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On Thu, Dec 6, 2018 at 5:37 PM Vlastimil Babka <vbabka@suse.cz> wrote:
>
> On 12/6/18 4:49 AM, Nicolas Boichat wrote:
> >> So it would be fine even unchanged. The check would anyway need some
> >> more love to catch the same with __GFP_DMA to be consistent and cover
> >> all corner cases.
> > Yes, the test is not complete. If we really wanted this to be
> > accurate, we'd need to check that GFP_* exactly matches SLAB_CACHE_*.
> >
> > The only problem with dropping this is test that we should restore
> > GFP_DMA32 warning/errors somewhere else (as Christopher pointed out
> > here: https://lkml.org/lkml/2018/11/22/430), especially for kmalloc
> > case.
>
> I meant just dropping that patch hunk, not the whole test. Then the test
> stays as it is and will keep warning anyone calling kmalloc(GFP_DMA32).
> It would also warn anyone calling kmem_cache_alloc(GFP_DMA32) on
> SLAB_CACHE_DMA32 cache, but since the gfp can be just dropped, and you
> as the only user of this so far will do that, it's fine?

I missed your point, this would work fine indeed.

Thanks.

> > Maybe this can be done in kmalloc_slab.