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

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Date:   Tue, 19 Jan 2021 12:36:40 -0800
From:   Minchan Kim <minchan@...nel.org>
To:     John Stultz <john.stultz@...aro.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Hyesoo Yu <hyesoo.yu@...sung.com>, 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 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.