Re: [PATCH v2 1/2] dma-contiguous: Abstract dma_{alloc, free}_contiguous()

[dann frazier <dann.frazier@canonical.com>]

On Mon, May 6, 2019 at 4:35 PM Nicolin Chen <nicoleotsuka@gmail.com> wrote:
>
> Both dma_alloc_from_contiguous() and dma_release_from_contiguous()
> are very simply implemented, but requiring callers to pass certain
> parameters like count and align, and taking a boolean parameter to
> check __GFP_NOWARN in the allocation flags. So every function call
> duplicates similar work:
>   /* A piece of example */
>   unsigned long order = get_order(size);
>   size_t count = size >> PAGE_SHIFT;
>   page = dma_alloc_from_contiguous(dev, count, order, gfp & __GFP_NOWARN);
>   [...]
>   dma_release_from_contiguous(dev, page, size >> PAGE_SHIFT);
>
> Additionally, as CMA can be used only in the context which permits
> sleeping, most of callers do a gfpflags_allow_blocking() check and
> a corresponding fallback allocation of normal pages upon any false
> result:
>   /* A piece of example */
>   if (gfpflags_allow_blocking(flag))
>       page = dma_alloc_from_contiguous();
>   if (!page)
>       page = alloc_pages();
>   [...]
>   if (!dma_release_from_contiguous(dev, page, count))
>       __free_pages(page, get_order(size));
>
> So this patch simplifies those function calls by abstracting these
> operations into the two new functions: dma_{alloc,free}_contiguous.
>
> As some callers of dma_{alloc,release}_from_contiguous() might be
> complicated, this patch just implements these two new functions to
> kernel/dma/direct.c only as an initial step.
>
> Suggested-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Nicolin Chen <nicoleotsuka@gmail.com>
> ---
> Changelog
> v1->v2:
>  * Added new functions beside the old ones so we can replace callers
>    one by one later.
>  * Applied new functions to dma/direct.c only, because it's the best
>    example caller to apply and should be safe with the new functions.
>
>  include/linux/dma-contiguous.h | 10 +++++++
>  kernel/dma/contiguous.c        | 48 ++++++++++++++++++++++++++++++++++
>  kernel/dma/direct.c            | 24 +++--------------
>  3 files changed, 62 insertions(+), 20 deletions(-)
>
> diff --git a/include/linux/dma-contiguous.h b/include/linux/dma-contiguous.h
> index f247e8aa5e3d..dacbdcb91a89 100644
> --- a/include/linux/dma-contiguous.h
> +++ b/include/linux/dma-contiguous.h
> @@ -115,6 +115,8 @@ struct page *dma_alloc_from_contiguous(struct device *dev, size_t count,
>                                        unsigned int order, bool no_warn);
>  bool dma_release_from_contiguous(struct device *dev, struct page *pages,
>                                  int count);
> +struct page *dma_alloc_contiguous(struct device *dev, size_t size, gfp_t gfp);
> +void dma_free_contiguous(struct device *dev, struct page *page, size_t size);
>
>  #else
>
> @@ -157,6 +159,14 @@ bool dma_release_from_contiguous(struct device *dev, struct page *pages,
>         return false;
>  }
>
> +struct page *dma_alloc_contiguous(struct device *dev, size_t size, gfp_t gfp)
> +{
> +       return NULL;
> +}
> +
> +static inline
> +void dma_free_contiguous(struct device *dev, struct page *page, size_t size) { }
> +
>  #endif
>
>  #endif
> diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c
> index b2a87905846d..21f39a6cb04f 100644
> --- a/kernel/dma/contiguous.c
> +++ b/kernel/dma/contiguous.c
> @@ -214,6 +214,54 @@ bool dma_release_from_contiguous(struct device *dev, struct page *pages,
>         return cma_release(dev_get_cma_area(dev), pages, count);
>  }

This breaks the build for me if CONFIG_DMA_CMA=n:

  LD [M]  fs/9p/9p.o
ld: fs/9p/vfs_inode.o: in function `dma_alloc_contiguous':
vfs_inode.c:(.text+0xa60): multiple definition of
`dma_alloc_contiguous'; fs/9p/vfs_super.o:vfs_super.c:(.text+0x500):
first defined here

Do the following insertions need to be under an #ifdef CONFIG_DMA_CMA ?

  -dann

> +/**
> + * dma_alloc_contiguous() - allocate contiguous pages
> + * @dev:   Pointer to device for which the allocation is performed.
> + * @size:  Requested allocation size.
> + * @gfp:   Allocation flags.
> + *
> + * This function allocates contiguous memory buffer for specified device. It
> + * first tries to use device specific contiguous memory area if available or
> + * the default global one, then tries a fallback allocation of normal pages.
> + */
> +struct page *dma_alloc_contiguous(struct device *dev, size_t size, gfp_t gfp)
> +{
> +       int node = dev ? dev_to_node(dev) : NUMA_NO_NODE;
> +       size_t count = PAGE_ALIGN(size) >> PAGE_SHIFT;
> +       size_t align = get_order(PAGE_ALIGN(size));
> +       struct cma *cma = dev_get_cma_area(dev);
> +       struct page *page = NULL;
> +
> +       /* CMA can be used only in the context which permits sleeping */
> +       if (cma && gfpflags_allow_blocking(gfp)) {
> +               align = min_t(size_t, align, CONFIG_CMA_ALIGNMENT);
> +               page = cma_alloc(cma, count, align, gfp & __GFP_NOWARN);
> +       }
> +
> +       /* Fallback allocation of normal pages */
> +       if (!page)
> +               page = alloc_pages_node(node, gfp, align);
> +
> +       return page;
> +}
> +
> +/**
> + * dma_free_contiguous() - release allocated pages
> + * @dev:   Pointer to device for which the pages were allocated.
> + * @page:  Pointer to the allocated pages.
> + * @size:  Size of allocated pages.
> + *
> + * This function releases memory allocated by dma_alloc_contiguous(). As the
> + * cma_release returns false when provided pages do not belong to contiguous
> + * area and true otherwise, this function then does a fallback __free_pages()
> + * upon a false-return.
> + */
> +void dma_free_contiguous(struct device *dev, struct page *page, size_t size)
> +{
> +       if (!cma_release(dev_get_cma_area(dev), page, size >> PAGE_SHIFT))
> +               __free_pages(page, get_order(size));
> +}
> +
>  /*
>   * Support for reserved memory regions defined in device tree
>   */
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> index 2c2772e9702a..0816c1e8b05a 100644
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -96,8 +96,6 @@ static bool dma_coherent_ok(struct device *dev, phys_addr_t phys, size_t size)
>  struct page *__dma_direct_alloc_pages(struct device *dev, size_t size,
>                 dma_addr_t *dma_handle, gfp_t gfp, unsigned long attrs)
>  {
> -       unsigned int count = PAGE_ALIGN(size) >> PAGE_SHIFT;
> -       int page_order = get_order(size);
>         struct page *page = NULL;
>         u64 phys_mask;
>
> @@ -109,20 +107,9 @@ struct page *__dma_direct_alloc_pages(struct device *dev, size_t size,
>         gfp |= __dma_direct_optimal_gfp_mask(dev, dev->coherent_dma_mask,
>                         &phys_mask);
>  again:
> -       /* CMA can be used only in the context which permits sleeping */
> -       if (gfpflags_allow_blocking(gfp)) {
> -               page = dma_alloc_from_contiguous(dev, count, page_order,
> -                                                gfp & __GFP_NOWARN);
> -               if (page && !dma_coherent_ok(dev, page_to_phys(page), size)) {
> -                       dma_release_from_contiguous(dev, page, count);
> -                       page = NULL;
> -               }
> -       }
> -       if (!page)
> -               page = alloc_pages_node(dev_to_node(dev), gfp, page_order);
> -
> +       page = dma_alloc_contiguous(dev, size, gfp);
>         if (page && !dma_coherent_ok(dev, page_to_phys(page), size)) {
> -               __free_pages(page, page_order);
> +               dma_free_contiguous(dev, page, size);
>                 page = NULL;
>
>                 if (IS_ENABLED(CONFIG_ZONE_DMA32) &&
> @@ -154,7 +141,7 @@ void *dma_direct_alloc_pages(struct device *dev, size_t size,
>         if (PageHighMem(page)) {
>                 /*
>                  * Depending on the cma= arguments and per-arch setup
> -                * dma_alloc_from_contiguous could return highmem pages.
> +                * dma_alloc_contiguous could return highmem pages.
>                  * Without remapping there is no way to return them here,
>                  * so log an error and fail.
>                  */
> @@ -176,10 +163,7 @@ void *dma_direct_alloc_pages(struct device *dev, size_t size,
>
>  void __dma_direct_free_pages(struct device *dev, size_t size, struct page *page)
>  {
> -       unsigned int count = PAGE_ALIGN(size) >> PAGE_SHIFT;
> -
> -       if (!dma_release_from_contiguous(dev, page, count))
> -               __free_pages(page, get_order(size));
> +       dma_free_contiguous(dev, page, size);
>  }
>
>  void dma_direct_free_pages(struct device *dev, size_t size, void *cpu_addr,
> --
> 2.17.1
>
>
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