linux-kernel - Re: [PATCH v3 4/4] dma-buf: heaps: add chunk heap to dmabuf heaps

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Date:   Wed, 20 Jan 2021 12:32:08 +0900
From:   Hyesoo Yu <hyesoo.yu@...sung.com>
To:     Minchan Kim <minchan@...nel.org>
Cc:     John Stultz <john.stultz@...aro.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>, david@...hat.com,
        Michal Hocko <mhocko@...e.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        KyongHo Cho <pullip.cho@...sung.com>,
        John Dias <joaodias@...gle.com>,
        Hridya Valsaraju <hridya@...gle.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        linux-media <linux-media@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Christoph Hellwig <hch@...radead.org>,
        Rob Herring <robh+dt@...nel.org>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@...ts.linaro.org>
Subject: Re: [PATCH v3 4/4] dma-buf: heaps: add chunk heap to dmabuf heaps

On Tue, Jan 19, 2021 at 12:36:40PM -0800, Minchan Kim wrote:
> On Tue, Jan 19, 2021 at 10:29:29AM -0800, John Stultz wrote:
> > On Tue, Jan 12, 2021 at 5:22 PM Minchan Kim <minchan@...nel.org> wrote:
> > >
> > > From: Hyesoo Yu <hyesoo.yu@...sung.com>
> > >
> > > This patch supports chunk heap that allocates the buffers that
> > > arranged into a list a fixed size chunks taken from CMA.
> > >
> > > The chunk heap driver is bound directly to a reserved_memory
> > > node by following Rob Herring's suggestion in [1].
> > >
> > > [1] https://lore.kernel.org/lkml/20191025225009.50305-2-john.stultz@linaro.org/T/#m3dc63acd33fea269a584f43bb799a876f0b2b45d
> > >
> > > Signed-off-by: Hyesoo Yu <hyesoo.yu@...sung.com>
> > > Signed-off-by: Hridya Valsaraju <hridya@...gle.com>
> > > Signed-off-by: Minchan Kim <minchan@...nel.org>
> > > ---
> > ...
> > > +static int register_chunk_heap(struct chunk_heap *chunk_heap_info)
> > > +{
> > > +       struct dma_heap_export_info exp_info;
> > > +
> > > +       exp_info.name = cma_get_name(chunk_heap_info->cma);
> > 
> > One potential issue here, you're setting the name to the same as the
> > CMA name. Since the CMA heap uses the CMA name, if one chunk was
> > registered as a chunk heap but also was the default CMA area, it might
> > be registered twice. But since both would have the same name it would
> > be an initialization race as to which one "wins".
> 
> Good point. Maybe someone might want to use default CMA area for
> both cma_heap and chunk_heap. I cannot come up with ideas why we
> should prohibit it atm.
> 
> > 
> > So maybe could you postfix the CMA name with "-chunk" or something?
> 
> Hyesoo, Any opinion?
> Unless you have something other idea, let's fix it in next version.
>

I agree that. It is not good to use heap name directly as cma name.
Let's postfix the name with '-chunk'

Thanks,
Regards.