linux-kernel - Re: [PATCH v2 4/4] dma-buf: heaps: add chunk heap to dmabuf heaps

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Date:   Tue, 1 Dec 2020 16:33:14 -0800
From:   John Stultz <john.stultz@...aro.org>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>, Hyesoo Yu <hyesoo.yu@...sung.com>,
        Matthew Wilcox <willy@...radead.org>, david@...hat.com,
        iamjoonsoo.kim@....com, vbabka@...e.cz,
        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>,
        Brian Starkey <Brian.Starkey@....com>,
        linux-media <linux-media@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, Rob Herring <robh@...nel.org>,
        Christian Koenig <christian.koenig@....com>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@...ts.linaro.org>
Subject: Re: [PATCH v2 4/4] dma-buf: heaps: add chunk heap to dmabuf heaps

On Tue, Dec 1, 2020 at 4:13 PM Minchan Kim <minchan@...nel.org> wrote:
>
> On Tue, Dec 01, 2020 at 03:38:14PM -0800, John Stultz wrote:
> > On Tue, Dec 1, 2020 at 2:55 PM Minchan Kim <minchan@...nel.org> wrote:
> > > On Tue, Dec 01, 2020 at 11:48:15AM -0800, John Stultz wrote:
> > > > On Tue, Dec 1, 2020 at 9:51 AM Minchan Kim <minchan@...nel.org> wrote:
> > > >
> > > > Thanks for reworking and resending this!
> > > >
> > > > ...
> > > > > +static int __init chunk_heap_init(void)
> > > > > +{
> > > > > +       struct cma *default_cma = dev_get_cma_area(NULL);
> > > > > +       struct dma_heap_export_info exp_info;
> > > > > +       struct chunk_heap *chunk_heap;
> > > > > +
> > > > > +       if (!default_cma)
> > > > > +               return 0;
> > > > > +
> > > > > +       chunk_heap = kzalloc(sizeof(*chunk_heap), GFP_KERNEL);
> > > > > +       if (!chunk_heap)
> > > > > +               return -ENOMEM;
> > > > > +
> > > > > +       chunk_heap->order = CHUNK_HEAP_ORDER;
> > > > > +       chunk_heap->cma = default_cma;
> > > > > +
> > > > > +       exp_info.name = cma_get_name(default_cma);
> > > >
> > > > So, this would create a chunk heap name with the default CMA name,
> > > > which would be indistinguishable from the heap name used for the plain
> > > > CMA heap.
> > > >
> > > > Probably a good idea to prefix it with "chunk-" so the heap device
> > > > names are unique?
> > >
> > > That will give an impression to user that they are using different CMA
> > > area but that's not true. IMHO, let's be honest at this moment.
> >
> > I disagree.  The dmabuf heaps provide an abstraction for allocating a
> > type of memory, and while your heap is pulling from CMA, you aren't
> > "just" allocating CMA as the existing CMA heap would suffice for that.
> >
> > Since you need a slightly different method to allocate high order
> > pages in bulk, we really should have a unique way to name the
> > allocator interface. That's why I'd suggest the "chunk-" prefix to the
> > heap name.
>
> Got it. How about this?
>
> diff --git a/drivers/dma-buf/heaps/chunk_heap.c b/drivers/dma-buf/heaps/chunk_heap.c
> index 0277707a93a9..36e189d0b73d 100644
> --- a/drivers/dma-buf/heaps/chunk_heap.c
> +++ b/drivers/dma-buf/heaps/chunk_heap.c
> @@ -410,7 +410,7 @@ static int __init chunk_heap_init(void)
>         chunk_heap->order = CHUNK_HEAP_ORDER;
>         chunk_heap->cma = default_cma;
>
> -       exp_info.name = cma_get_name(default_cma);
> +       exp_info.name = "cma-chunk-heap";

That's still a bit general for the default cma (which can be named
differently). I think including cma name is important, just adding the
chunk prefix might be best.

So something like
  sprintf(buf, "chunk-%s", cma_get_name(default_cma));
  exp_info.name = buf;

thanks
-john