Re: [PATCH v4 1/2] dma-direct: provide the ability to reserve per-numa CMA

Christoph Hellwig
2020-07-28T11:52:53Z

On Fri, Jul 24, 2020 at 01:13:43AM +1200, Barry Song wrote:
> +config CMA_PERNUMA_SIZE_MBYTES
> + int "Size in Mega Bytes for per-numa CMA areas"
> + depends on NUMA
> + default 16 if ARM64
> + default 0
> + help
> + Defines the size (in MiB) of the per-numa memory area for Contiguous
> + Memory Allocator. Every numa node will get a separate CMA with this
> + size. If the size of 0 is selected, per-numa CMA is disabled.

I'm still not a fan of the config option. You can just hardcode the
value in CONFIG_CMDLINE based on the kernel parameter. Also I wonder
if a way to expose this in the device tree might be useful, but people
more familiar with the device tree and the arm code will have to chime
in on that.

> struct cma *dma_contiguous_default_area;
> +static struct cma *dma_contiguous_pernuma_area[MAX_NUMNODES];
>
> /*
> * Default global CMA area size can be defined in kernel's .config.
> @@ -44,6 +51,8 @@ struct cma *dma_contiguous_default_area;
> */
> static const phys_addr_t size_bytes __initconst =
> (phys_addr_t)CMA_SIZE_MBYTES * SZ_1M;
> +static phys_addr_t pernuma_size_bytes __initdata =
> + (phys_addr_t)CMA_SIZE_PERNUMA_MBYTES * SZ_1M;
> static phys_addr_t size_cmdline __initdata = -1;
> static phys_addr_t base_cmdline __initdata;
> static phys_addr_t limit_cmdline __initdata;
> @@ -69,6 +78,13 @@ static int __init early_cma(char *p)
> }
> early_param("cma", early_cma);
>
> +static int __init early_pernuma_cma(char *p)
> +{
> + pernuma_size_bytes = memparse(p, &p);
> + return 0;
> +}
> +early_param("pernuma_cma", early_pernuma_cma);
> +
> #ifdef CONFIG_CMA_SIZE_PERCENTAGE
>
> static phys_addr_t __init __maybe_unused cma_early_percent_memory(void)
> @@ -96,6 +112,33 @@ static inline __maybe_unused phys_addr_t cma_early_percent_memory(void)
>
> #endif
>
> +void __init dma_pernuma_cma_reserve(void)
> +{
> + int nid;
> +
> + if (!pernuma_size_bytes)
> + return;
> +
> + for_each_node_state(nid, N_MEMORY) {
> + int ret;
> + char name[20];
> +
> + snprintf(name, sizeof(name), "pernuma%d", nid);
> + ret = cma_declare_contiguous_nid(0, pernuma_size_bytes, 0, 0,
> + 0, false, name,
> + &dma_contiguous_pernuma_area[nid],
> + nid);

This adds a > 80 char line.

> struct page *dma_alloc_contiguous(struct device *dev, size_t size, gfp_t gfp)
> {
> + int nid = dev_to_node(dev);
> +
> /* CMA can be used only in the context which permits sleeping */
> if (!gfpflags_allow_blocking(gfp))
> return NULL;
> if (dev->cma_area)
> return cma_alloc_aligned(dev->cma_area, size, gfp);
> - if (size <= PAGE_SIZE || !dma_contiguous_default_area)
> + if (size <= PAGE_SIZE)
> return NULL;
> +
> + if ((nid != NUMA_NO_NODE) && !(gfp & (GFP_DMA | GFP_DMA32))) {

No need for the braces around the nid check.

> + struct cma *cma = dma_contiguous_pernuma_area[nid];
> + struct page *page;
> +
> + if (cma) {
> + page = cma_alloc_aligned(cma, size, gfp);
> + if (page)
> + return page;
> + }
> + }
> +
> return cma_alloc_aligned(dma_contiguous_default_area, size, gfp);

This seems to have lost the dma_contiguous_default_area NULL check.

> + /* if dev has its own cma, free page from there */
> + if (dev->cma_area) {
> + if (cma_release(dev->cma_area, page, PAGE_ALIGN(size) >> PAGE_SHIFT))
> + return;

Another overly long line.

> + } else {
> + /*
> + * otherwise, page is from either per-numa cma or default cma
> + */
> + if (cma_release(dma_contiguous_pernuma_area[page_to_nid(page)],
> + page, PAGE_ALIGN(size) >> PAGE_SHIFT))
> + return;
> +
> + if (cma_release(dma_contiguous_default_area, page,
> + PAGE_ALIGN(size) >> PAGE_SHIFT))
> + return;
> + }

I'd introduce a count variable for the value of "PAGE_ALIGN(size) >>
PAGE_SHIFT" to clean al lthis up a bit.

Also please add a CONFIG_PERCPU_DMA_CMA config variable so that we
don't build this code for the vast majority of users that don't need it.