linux-kernel - Re: [PATCH v6 4/5] dma-buf: heaps: Add CMA heap to dmabuf heaps

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Message-ID: <20190725124524.GB20286@infradead.org>
Date:   Thu, 25 Jul 2019 05:45:24 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Benjamin Gaignard <benjamin.gaignard@...aro.org>
Cc:     Christoph Hellwig <hch@...radead.org>,
        John Stultz <john.stultz@...aro.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Laura Abbott <labbott@...hat.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Liam Mark <lmark@...eaurora.org>,
        Pratik Patel <pratikp@...eaurora.org>,
        Brian Starkey <Brian.Starkey@....com>,
        Vincent Donnefort <Vincent.Donnefort@....com>,
        Sudipto Paul <Sudipto.Paul@....com>,
        "Andrew F . Davis" <afd@...com>,
        Xu YiPing <xuyiping@...ilicon.com>,
        "Chenfeng (puck)" <puck.chen@...ilicon.com>,
        butao <butao@...ilicon.com>,
        "Xiaqing (A)" <saberlily.xia@...ilicon.com>,
        Yudongbin <yudongbin@...ilicon.com>,
        Chenbo Feng <fengc@...gle.com>,
        Alistair Strachan <astrachan@...gle.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH v6 4/5] dma-buf: heaps: Add CMA heap to dmabuf heaps

On Wed, Jul 24, 2019 at 10:08:54AM +0200, Benjamin Gaignard wrote:
> CMA has made possible to get large regions of memories and to give some
> priority on device allocating pages on it. I don't think that possible
> with system
> heap so I suggest to keep CMA heap if we want to be able to port a maximum
> of applications on dma-buf-heap.

Yes, CMA is a way to better allocate contigous regions, but it isn't
the only way to do that.

So at least for the system default CMA area it really should be a helper
for the system heap, especially given that CMA is an optional feature
and we can do high order contigous allocations using alloc_pages as
well.

Something like:

	if (!require_contigous && order > 0) {
		for (i = 0; i < nr_pages; i++)
			page[i] = alloc_page();
		goto done;
	} else if (order > 0)
		page = cma_alloc();
		if (page)
			goto done;
	}

	page = alloc_pages(order);