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

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Date:   Wed, 2 Dec 2020 13:54:22 +0000
From:   Christoph Hellwig <hch@...radead.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@...sung.com,
        willy@...radead.org, david@...hat.com, iamjoonsoo.kim@....com,
        vbabka@...e.cz, surenb@...gle.com, pullip.cho@...sung.com,
        joaodias@...gle.com, hridya@...gle.com, sumit.semwal@...aro.org,
        john.stultz@...aro.org, Brian.Starkey@....com,
        linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        robh@...nel.org, christian.koenig@....com,
        linaro-mm-sig@...ts.linaro.org
Subject: Re: [PATCH v2 4/4] dma-buf: heaps: add chunk heap to dmabuf heaps

On Tue, Dec 01, 2020 at 09:51:44AM -0800, Minchan Kim 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 doesn't use heap-helper although it can remove
> duplicated code since heap-helper is under deprecated process.[1]
> 
> NOTE: This patch only adds the default CMA heap to allocate chunk
> pages. We will add another CMA memory regions to the dmabuf heaps
> interface with a later patch (which requires a dt binding)

This new heap seems to largely duplicate the exsting cma_heap.c
file.  Why can't you reuse the code and allow creating different
heaps with different chunk sizes or max numbers of segments?

> +config DMABUF_HEAPS_CHUNK_ORDER
> +	int "Chunk page order for dmabuf chunk heap"
> +	default 4
> +	depends on DMABUF_HEAPS_CHUNK
> +	help
> +	  Set page order of fixed chunk size to allocate from CMA.

Using a config option for this is just broken.  It needs to be runtime
or at very least boot time / DT controllable.

> + * ION Memory Allocator chunk heap exporter

This comment seems wrong.