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SubjectRe: [RFC PATCH] cma: make number of CMA areas dynamic, remove CONFIG_CMA_AREAS
On Wed, Sep 02, 2020 at 08:02:04PM -0700, Mike Kravetz wrote:
> --- a/arch/arm/mm/dma-mapping.c
> +++ b/arch/arm/mm/dma-mapping.c
> @@ -383,25 +383,34 @@ postcore_initcall(atomic_pool_init);
> struct dma_contig_early_reserve {
> phys_addr_t base;
> unsigned long size;
> + struct list_head areas;
> };
>
> +static __initdata LIST_HEAD(dma_mmu_remap_areas);
>
> void __init dma_contiguous_early_fixup(phys_addr_t base, unsigned long size)
> {
> + struct dma_contig_early_reserve *d;
> +
> + d = memblock_alloc(sizeof(struct dma_contig_early_reserve),
> + sizeof(void *));
> + if (!d) {
> + pr_err("Unable to allocate dma_contig_early_reserve struct!\n");
> + return;
> + }
> +
> + d->base = base;
> + d->size = size;
> + list_add_tail(&d->areas, &dma_mmu_remap_areas);
> }

I wonder if struct cma should grow a flags or type field, so that the
arm code can simply use cma_for_each_area to iterate the CMA areas for
the DMA fixup, and we can remove the extra list and the magic hook.

> +/* modify here */
> +LIST_HEAD(cma_areas);

What does this comment mean?

> +static unsigned int cma_area_count;

It seems this is only used to provide a default name for the CMA
areas, but all areas actually provide a name, so I think we can drop
the default naming and the cma_area_count variable entirely.

> if (!size || !memblock_is_region_reserved(base, size))
> return -EINVAL;
>
> +
> /* ensure minimal alignment required by mm core */

This adds a spurious empty line.

> static int __init cma_debugfs_init(void)
> {
> struct dentry *cma_debugfs_root;
> - int i;
> + struct cma *c;
>
> cma_debugfs_root = debugfs_create_dir("cma", NULL);
>
> - for (i = 0; i < cma_area_count; i++)
> - cma_debugfs_add_one(&cma_areas[i], cma_debugfs_root);
> + list_for_each_entry(c, &cma_areas, areas)
> + cma_debugfs_add_one(c, cma_debugfs_root);

I think this should use cma_for_each_area, that way cma_areas can be
keep static in cma.c.

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