Re: [PATCH v3 1/2] dma-contiguous: Abstract dma_{alloc,free}_contiguous()

Nicolin Chen
2019-07-25T16:49:36Z

On Thu, Jul 25, 2019 at 01:06:42PM -0300, Ezequiel Garcia wrote:
> I can't find a way to forward-redirect from Gmail, so I'm Ccing Dafna
> who found a regression caused by this commit. Dafna, can you give all
> the details, including the log and how you are reproducing it?

I saw the conversation there. Sorry for not replying yet.
May we discuss there since there are full logs available?

Thanks
Nicolin

>
>
> On Fri, 24 May 2019 at 01:08, 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
> > v2->v3:
> > * Added missing "static inline" in header file to fix build error.
> > 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 | 11 ++++++++
> > kernel/dma/contiguous.c | 48 ++++++++++++++++++++++++++++++++++
> > kernel/dma/direct.c | 24 +++--------------
> > 3 files changed, 63 insertions(+), 20 deletions(-)
> >
> > diff --git a/include/linux/dma-contiguous.h b/include/linux/dma-contiguous.h
> > index f247e8aa5e3d..00a370c1c140 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 +159,15 @@ bool dma_release_from_contiguous(struct device *dev, struct page *pages,
> > return false;
> > }
> >
> > +static inline
> > +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);
> > }
> >
> > +/**
> > + * 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
> >