Re: [RFC HMM CDM 3/3] mm/migrate: memory migration using a device DMA engine

[Reza Arbab]

(Had sent this to you directly. Reposting for the whole cc list.)

On Fri, Apr 07, 2017 at 04:28:53PM -0400, Jérôme Glisse wrote:
> --- a/include/linux/migrate.h
> +++ b/include/linux/migrate.h 
> @@ -212,28 +215,25 @@ static inline unsigned long migrate_pfn(unsigned long pfn)
>  * THE finalize_and_map() CALLBACK MUST NOT CHANGE ANY OF THE SRC OR DST ARRAY
>  * ENTRIES OR BAD THINGS WILL HAPPEN !
>  */
> -struct migrate_vma_ops {
> -	void (*alloc_and_copy)(struct vm_area_struct *vma,
> -			       const unsigned long *src,
> -			       unsigned long *dst,
> -			       unsigned long start,
> -			       unsigned long end,
> -			       void *private);
> -	void (*finalize_and_map)(struct vm_area_struct *vma,
> -				 const unsigned long *src,
> -				 const unsigned long *dst,
> -				 unsigned long start,
> -				 unsigned long end,
> -				 void *private);
> +struct migrate_dma_ops {
> +	void (*alloc_and_copy)(struct migrate_dma_ctx *ctx);
> +	void (*finalize_and_map)(struct migrate_dma_ctx *ctx);
> +};
> +
> +struct migrate_dma_ctx {
> +	const struct migrate_dma_ops	*ops;
> +	unsigned long			*dst;
> +	unsigned long			*src;
> +	unsigned long			cpages;
> +	unsigned long			npages;

Could you add this so we can still pass arguments to the callbacks?

	void				*private;

> };
>
> -int migrate_vma(const struct migrate_vma_ops *ops,
> +int migrate_vma(struct migrate_dma_ctx *ctx,
> 		struct vm_area_struct *vma,
> 		unsigned long start,
> -		unsigned long end,
> -		unsigned long *src,
> -		unsigned long *dst,
> -		void *private);
> +		unsigned long end);
> +int migrate_dma(struct migrate_dma_ctx *migrate_ctx);
> +
>
> #endif /* CONFIG_MIGRATION */

...%<...

> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -2803,16 +2761,76 @@ int migrate_vma(const struct migrate_vma_ops *ops,
> 	 * Note that migration can fail in migrate_vma_struct_page() for each
> 	 * individual page.
> 	 */
> -	ops->alloc_and_copy(vma, src, dst, start, end, private);
> +	migrate_ctx->ops->alloc_and_copy(migrate_ctx);
>
> 	/* This does the real migration of struct page */
> -	migrate_vma_pages(&migrate);
> +	migrate_dma_pages(migrate_ctx, vma, start, end);
>
> -	ops->finalize_and_map(vma, src, dst, start, end, private);
> +	migrate_ctx->ops->finalize_and_map(migrate_ctx);
>
> 	/* Unlock and remap pages */
> -	migrate_vma_finalize(&migrate);
> +	migrate_dma_finalize(migrate_ctx);
>
> 	return 0;
> }
> EXPORT_SYMBOL(migrate_vma);
> +
> +/*
> + * migrate_dma() - migrate an array of pages using a device DMA engine
> + *
> + * @migrate_ctx: migrate context structure
> + *
> + * The context structure must have its src fields pointing to an array of
> + * migrate pfn entry each corresponding to a valid page and each page being
> + * lock. The dst entry must by an array as big as src, it will be use during
> + * migration to store the destination pfn.
> + *
> + */
> +int migrate_dma(struct migrate_dma_ctx *migrate_ctx)
> +{
> +	unsigned long i;
> +
> +	/* Sanity check the arguments */
> +	if (!migrate_ctx->ops || !migrate_ctx->src || !migrate_ctx->dst)
> +		return -EINVAL;
> +
> +	/* Below code should be hidden behind some DEBUG config */
> +	for (i = 0; i < migrate_ctx->npages; ++i) {
> +		const unsigned long mask = MIGRATE_PFN_VALID |
> +					   MIGRATE_PFN_LOCKED;

This line is before the pages are locked. I think it should be

					   MIGRATE_PFN_MIGRATE;

> +
> +		if (!(migrate_ctx->src[i] & mask))
> +			return -EINVAL;
> +	}
> +
> +	/* Lock and isolate page */
> +	migrate_dma_prepare(migrate_ctx);
> +	if (!migrate_ctx->cpages)
> +		return 0;
> +
> +	/* Unmap pages */
> +	migrate_dma_unmap(migrate_ctx);
> +	if (!migrate_ctx->cpages)
> +		return 0;
> +
> +	/*
> +	 * At this point pages are locked and unmapped, and thus they have
> +	 * stable content and can safely be copied to destination memory that
> +	 * is allocated by the callback.
> +	 *
> +	 * Note that migration can fail in migrate_vma_struct_page() for each
> +	 * individual page.
> +	 */
> +	migrate_ctx->ops->alloc_and_copy(migrate_ctx);
> +
> +	/* This does the real migration of struct page */
> +	migrate_dma_pages(migrate_ctx, NULL, 0, 0);
> +
> +	migrate_ctx->ops->finalize_and_map(migrate_ctx);
> +
> +	/* Unlock and remap pages */
> +	migrate_dma_finalize(migrate_ctx);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(migrate_dma);

--
Reza Arbab