Message-ID: <4FBB4142.2070709@kernel.org>
Date:	Tue, 22 May 2012 16:33:22 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	linux-kernel@...r.kernel.org
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2 4/4] ARM: dma-mapping: remove custom consistent dma
 region

On 05/17/2012 07:54 PM, Marek Szyprowski wrote:

> This patch changes dma-mapping subsystem to use generic vmalloc areas
> for all consistent dma allocations. This increases the total size limit
> of the consistent allocations and removes platform hacks and a lot of
> duplicated code.
> 


I like this patch very much!
There are just small nitpicks below.

> Atomic allocations are served from special pool preallocated on boot,
> becasue vmalloc areas cannot be reliably created in atomic context.


typo because

>

> Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>
> ---
>  Documentation/kernel-parameters.txt |    4 +
>  arch/arm/include/asm/dma-mapping.h  |    2 +-
>  arch/arm/mm/dma-mapping.c           |  360 ++++++++++++++++-------------------
>  3 files changed, 171 insertions(+), 195 deletions(-)
> 
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index c1601e5..ba58f50 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -515,6 +515,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
>  			a hypervisor.
>  			Default: yes
>  
> +	coherent_pool=nn[KMG]	[ARM,KNL]
> +			Sets the size of memory pool for coherent, atomic dma
> +			allocations.
> +
>  	code_bytes	[X86] How many bytes of object code to print
>  			in an oops report.
>  			Range: 0 - 8192
> diff --git a/arch/arm/include/asm/dma-mapping.h b/arch/arm/include/asm/dma-mapping.h
> index cb3b7c9..92b0afb 100644
> --- a/arch/arm/include/asm/dma-mapping.h
> +++ b/arch/arm/include/asm/dma-mapping.h
> @@ -210,7 +210,7 @@ int dma_mmap_writecombine(struct device *, struct vm_area_struct *,
>   * DMA region above it's default value of 2MB. It must be called before the
>   * memory allocator is initialised, i.e. before any core_initcall.
>   */
> -extern void __init init_consistent_dma_size(unsigned long size);
> +static inline void init_consistent_dma_size(unsigned long size) { }
>  
>  
>  #ifdef CONFIG_DMABOUNCE
> diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
> index db23ae4..3be4de2 100644
> --- a/arch/arm/mm/dma-mapping.c
> +++ b/arch/arm/mm/dma-mapping.c
> @@ -19,6 +19,8 @@
>  #include <linux/dma-mapping.h>
>  #include <linux/highmem.h>
>  #include <linux/slab.h>
> +#include <linux/io.h>
> +#include <linux/vmalloc.h>
>  
>  #include <asm/memory.h>
>  #include <asm/highmem.h>
> @@ -119,210 +121,178 @@ static void __dma_free_buffer(struct page *page, size_t size)
>  }
>  
>  #ifdef CONFIG_MMU
> -
> -#define CONSISTENT_OFFSET(x)	(((unsigned long)(x) - consistent_base) >> PAGE_SHIFT)
> -#define CONSISTENT_PTE_INDEX(x) (((unsigned long)(x) - consistent_base) >> PMD_SHIFT)
> -
> -/*
> - * These are the page tables (2MB each) covering uncached, DMA consistent allocations
> - */
> -static pte_t **consistent_pte;
> -
> -#define DEFAULT_CONSISTENT_DMA_SIZE SZ_2M
> -
> -unsigned long consistent_base = CONSISTENT_END - DEFAULT_CONSISTENT_DMA_SIZE;
> -
> -void __init init_consistent_dma_size(unsigned long size)
> -{
> -	unsigned long base = CONSISTENT_END - ALIGN(size, SZ_2M);
> -
> -	BUG_ON(consistent_pte); /* Check we're called before DMA region init */
> -	BUG_ON(base < VMALLOC_END);
> -
> -	/* Grow region to accommodate specified size  */
> -	if (base < consistent_base)
> -		consistent_base = base;
> -}
> -
> -#include "vmregion.h"
> -
> -static struct arm_vmregion_head consistent_head = {
> -	.vm_lock	= __SPIN_LOCK_UNLOCKED(&consistent_head.vm_lock),
> -	.vm_list	= LIST_HEAD_INIT(consistent_head.vm_list),
> -	.vm_end		= CONSISTENT_END,
> -};
> -
>  #ifdef CONFIG_HUGETLB_PAGE
>  #error ARM Coherent DMA allocator does not (yet) support huge TLB
>  #endif
>  
> -/*
> - * Initialise the consistent memory allocation.
> - */
> -static int __init consistent_init(void)
> -{
> -	int ret = 0;
> -	pgd_t *pgd;
> -	pud_t *pud;
> -	pmd_t *pmd;
> -	pte_t *pte;
> -	int i = 0;
> -	unsigned long base = consistent_base;
> -	unsigned long num_ptes = (CONSISTENT_END - base) >> PMD_SHIFT;
> -
> -	consistent_pte = kmalloc(num_ptes * sizeof(pte_t), GFP_KERNEL);
> -	if (!consistent_pte) {
> -		pr_err("%s: no memory\n", __func__);
> -		return -ENOMEM;
> -	}
> -
> -	pr_debug("DMA memory: 0x%08lx - 0x%08lx:\n", base, CONSISTENT_END);
> -	consistent_head.vm_start = base;
> -
> -	do {
> -		pgd = pgd_offset(&init_mm, base);
> -
> -		pud = pud_alloc(&init_mm, pgd, base);
> -		if (!pud) {
> -			printk(KERN_ERR "%s: no pud tables\n", __func__);
> -			ret = -ENOMEM;
> -			break;
> -		}
> -
> -		pmd = pmd_alloc(&init_mm, pud, base);
> -		if (!pmd) {
> -			printk(KERN_ERR "%s: no pmd tables\n", __func__);
> -			ret = -ENOMEM;
> -			break;
> -		}
> -		WARN_ON(!pmd_none(*pmd));
> -
> -		pte = pte_alloc_kernel(pmd, base);
> -		if (!pte) {
> -			printk(KERN_ERR "%s: no pte tables\n", __func__);
> -			ret = -ENOMEM;
> -			break;
> -		}
> -
> -		consistent_pte[i++] = pte;
> -		base += PMD_SIZE;
> -	} while (base < CONSISTENT_END);
> -
> -	return ret;
> -}
> -
> -core_initcall(consistent_init);
> -
>  static void *
>  __dma_alloc_remap(struct page *page, size_t size, gfp_t gfp, pgprot_t prot,
>  	const void *caller)
>  {
> -	struct arm_vmregion *c;
> -	size_t align;
> -	int bit;
> +	struct vm_struct *area;
> +	unsigned long addr;
>  
> -	if (!consistent_pte) {
> -		printk(KERN_ERR "%s: not initialised\n", __func__);
> +	area = get_vm_area_caller(size, VM_DMA | VM_USERMAP, caller);


Out of curiosity.
Do we always map dma area into user's address space?

> +	if (!area)
> +		return NULL;
> +	addr = (unsigned long)area->addr;
> +	area->phys_addr = __pfn_to_phys(page_to_pfn(page));
> +
> +	if (ioremap_page_range(addr, addr + size, area->phys_addr, prot)) {
> +		vunmap((void *)addr);

> +		return NULL;

> +	}
> +	return (void *)addr;
> +}
> +
> +static void __dma_free_remap(void *cpu_addr, size_t size)
> +{
> +	struct vm_struct *area;
> +
> +	read_lock(&vmlist_lock);


Why do we need vmlist_lock?

> +	area = find_vm_area(cpu_addr);


find_vm_area only checks vmalloced regions so we need more check.

if (!area || !(area->flags & VM_DMA))

> +	if (!area) {
> +		pr_err("%s: trying to free invalid coherent area: %p\n",
> +		       __func__, cpu_addr);
> +		dump_stack();
> +		read_unlock(&vmlist_lock);
> +		return;
> +	}
> +	unmap_kernel_range((unsigned long)cpu_addr, size);
> +	read_unlock(&vmlist_lock);
> +	vunmap(cpu_addr);
> +}
> +
> +struct dma_pool {
> +	size_t size;
> +	spinlock_t lock;
> +	unsigned long *bitmap;
> +	unsigned long count;


Nitpick. What does count mean?
nr_pages?

> +	void *vaddr;
> +	struct page *page;
> +};
> +
> +static struct dma_pool atomic_pool = {
> +	.size = SZ_256K,
> +};


AFAIUC, we could set it to 2M but you are reducing it to 256K.
What's the justification for that default value?

> +
> +static int __init early_coherent_pool(char *p)
> +{
> +	atomic_pool.size = memparse(p, &p);
> +	return 0;
> +}
> +early_param("coherent_pool", early_coherent_pool);
> +
> +/*
> + * Initialise the coherent pool for atomic allocations.
> + */
> +static int __init atomic_pool_init(void)
> +{
> +	struct dma_pool *pool = &atomic_pool;
> +	pgprot_t prot = pgprot_dmacoherent(pgprot_kernel);
> +	unsigned long count = pool->size >> PAGE_SHIFT;
> +	gfp_t gfp = GFP_KERNEL | GFP_DMA;
> +	unsigned long *bitmap;
> +	struct page *page;
> +	void *ptr;
> +	int bitmap_size = BITS_TO_LONGS(count) * sizeof(long);
> +
> +	bitmap = kzalloc(bitmap_size, GFP_KERNEL);
> +	if (!bitmap)
> +		goto no_bitmap;
> +
> +	page = __dma_alloc_buffer(NULL, pool->size, gfp);
> +	if (!page)
> +		goto no_page;
> +
> +	ptr = __dma_alloc_remap(page, pool->size, gfp, prot, NULL);
> +	if (ptr) {
> +		spin_lock_init(&pool->lock);
> +		pool->vaddr = ptr;
> +		pool->page = page;
> +		pool->bitmap = bitmap;
> +		pool->count = count;
> +		pr_info("DMA: preallocated %u KiB pool for atomic coherent allocations\n",
> +		       (unsigned)pool->size / 1024);
> +		return 0;
> +	}
> +
> +	__dma_free_buffer(page, pool->size);
> +no_page:
> +	kfree(bitmap);
> +no_bitmap:
> +	pr_err("DMA: failed to allocate %u KiB pool for atomic coherent allocation\n",
> +	       (unsigned)pool->size / 1024);
> +	return -ENOMEM;
> +}
> +core_initcall(atomic_pool_init);
> +
> +static void *__alloc_from_pool(size_t size, struct page **ret_page)
> +{
> +	struct dma_pool *pool = &atomic_pool;
> +	unsigned int count = size >> PAGE_SHIFT;
> +	unsigned int pageno;
> +	unsigned long flags;
> +	void *ptr = NULL;
> +	size_t align;
> +
> +	if (!pool->vaddr) {
> +		pr_err("%s: coherent pool not initialised!\n", __func__);
>  		dump_stack();
>  		return NULL;
>  	}
>  
>  	/*
> -	 * Align the virtual region allocation - maximum alignment is
> -	 * a section size, minimum is a page size.  This helps reduce
> -	 * fragmentation of the DMA space, and also prevents allocations
> -	 * smaller than a section from crossing a section boundary.
> +	 * Align the region allocation - allocations from pool are rather
> +	 * small, so align them to their order in pages, minimum is a page
> +	 * size. This helps reduce fragmentation of the DMA space.
>  	 */
> -	bit = fls(size - 1);
> -	if (bit > SECTION_SHIFT)
> -		bit = SECTION_SHIFT;
> -	align = 1 << bit;
> +	align = PAGE_SIZE << get_order(size);
>  
> -	/*
> -	 * Allocate a virtual address in the consistent mapping region.
> -	 */
> -	c = arm_vmregion_alloc(&consistent_head, align, size,
> -			    gfp & ~(__GFP_DMA | __GFP_HIGHMEM), caller);
> -	if (c) {
> -		pte_t *pte;
> -		int idx = CONSISTENT_PTE_INDEX(c->vm_start);
> -		u32 off = CONSISTENT_OFFSET(c->vm_start) & (PTRS_PER_PTE-1);
> -
> -		pte = consistent_pte[idx] + off;
> -		c->vm_pages = page;
> -
> -		do {
> -			BUG_ON(!pte_none(*pte));
> -
> -			set_pte_ext(pte, mk_pte(page, prot), 0);
> -			page++;
> -			pte++;
> -			off++;
> -			if (off >= PTRS_PER_PTE) {
> -				off = 0;
> -				pte = consistent_pte[++idx];
> -			}
> -		} while (size -= PAGE_SIZE);
> -
> -		dsb();
> -
> -		return (void *)c->vm_start;
> +	spin_lock_irqsave(&pool->lock, flags);
> +	pageno = bitmap_find_next_zero_area(pool->bitmap, pool->count,
> +					    0, count, (1 << align) - 1);
> +	if (pageno < pool->count) {
> +		bitmap_set(pool->bitmap, pageno, count);
> +		ptr = pool->vaddr + PAGE_SIZE * pageno;
> +		*ret_page = pool->page + pageno;
>  	}
> -	return NULL;
> +	spin_unlock_irqrestore(&pool->lock, flags);
> +
> +	return ptr;
>  }
>  
> -static void __dma_free_remap(void *cpu_addr, size_t size)
> +static int __free_from_pool(void *start, size_t size)
>  {
> -	struct arm_vmregion *c;
> -	unsigned long addr;
> -	pte_t *ptep;
> -	int idx;
> -	u32 off;
> +	struct dma_pool *pool = &atomic_pool;
> +	unsigned long pageno, count;
> +	unsigned long flags;
>  
> -	c = arm_vmregion_find_remove(&consistent_head, (unsigned long)cpu_addr);
> -	if (!c) {
> -		printk(KERN_ERR "%s: trying to free invalid coherent area: %p\n",
> -		       __func__, cpu_addr);
> +	if (start < pool->vaddr || start > pool->vaddr + pool->size)
> +		return 0;
> +
> +	if (start + size > pool->vaddr + pool->size) {
> +		pr_err("%s: freeing wrong coherent size from pool\n", __func__);
>  		dump_stack();
> -		return;
> +		return 0;
>  	}
>  
> -	if ((c->vm_end - c->vm_start) != size) {
> -		printk(KERN_ERR "%s: freeing wrong coherent size (%ld != %d)\n",
> -		       __func__, c->vm_end - c->vm_start, size);
> -		dump_stack();
> -		size = c->vm_end - c->vm_start;
> -	}
> +	pageno = (start - pool->vaddr) >> PAGE_SHIFT;
> +	count = size >> PAGE_SHIFT;
>  
> -	idx = CONSISTENT_PTE_INDEX(c->vm_start);
> -	off = CONSISTENT_OFFSET(c->vm_start) & (PTRS_PER_PTE-1);
> -	ptep = consistent_pte[idx] + off;
> -	addr = c->vm_start;
> -	do {
> -		pte_t pte = ptep_get_and_clear(&init_mm, addr, ptep);
> +	spin_lock_irqsave(&pool->lock, flags);
> +	bitmap_clear(pool->bitmap, pageno, count);
> +	spin_unlock_irqrestore(&pool->lock, flags);
>  
> -		ptep++;
> -		addr += PAGE_SIZE;
> -		off++;
> -		if (off >= PTRS_PER_PTE) {
> -			off = 0;
> -			ptep = consistent_pte[++idx];
> -		}
> -
> -		if (pte_none(pte) || !pte_present(pte))
> -			printk(KERN_CRIT "%s: bad page in kernel page table\n",
> -			       __func__);
> -	} while (size -= PAGE_SIZE);
> -
> -	flush_tlb_kernel_range(c->vm_start, c->vm_end);
> -
> -	arm_vmregion_free(&consistent_head, c);
> +	return 1;
>  }
>  
>  #else	/* !CONFIG_MMU */
>  
>  #define __dma_alloc_remap(page, size, gfp, prot, c)	page_address(page)
>  #define __dma_free_remap(addr, size)			do { } while (0)
> +#define __alloc_from_pool(size, ret_page)		NULL
> +#define __free_from_pool(addr, size)			0
>  
>  #endif	/* CONFIG_MMU */
>  
> @@ -345,6 +315,16 @@ __dma_alloc(struct device *dev, size_t size, dma_addr_t *handle, gfp_t gfp,
>  	*handle = ~0;
>  	size = PAGE_ALIGN(size);
>  
> +	/*
> +	 * Atomic allocations need special handling
> +	 */
> +	if (gfp & GFP_ATOMIC && !arch_is_coherent()) {
> +		addr = __alloc_from_pool(size, &page);
> +		if (addr)
> +			*handle = pfn_to_dma(dev, page_to_pfn(page));
> +		return addr;
> +	}
> +
>  	page = __dma_alloc_buffer(dev, size, gfp);
>  	if (!page)
>  		return NULL;
> @@ -398,24 +378,16 @@ static int dma_mmap(struct device *dev, struct vm_area_struct *vma,
>  {
>  	int ret = -ENXIO;
>  #ifdef CONFIG_MMU
> -	unsigned long user_size, kern_size;
> -	struct arm_vmregion *c;
> +	unsigned long user_count = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
> +	unsigned long count = PAGE_ALIGN(size) >> PAGE_SHIFT;
> +	unsigned long pfn = dma_to_pfn(dev, dma_addr);
> +	unsigned long off = vma->vm_pgoff;
>  
> -	user_size = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
> -
> -	c = arm_vmregion_find(&consistent_head, (unsigned long)cpu_addr);
> -	if (c) {
> -		unsigned long off = vma->vm_pgoff;
> -
> -		kern_size = (c->vm_end - c->vm_start) >> PAGE_SHIFT;
> -
> -		if (off < kern_size &&
> -		    user_size <= (kern_size - off)) {
> -			ret = remap_pfn_range(vma, vma->vm_start,
> -					      page_to_pfn(c->vm_pages) + off,
> -					      user_size << PAGE_SHIFT,
> -					      vma->vm_page_prot);
> -		}
> +	if (off < count && user_count <= (count - off)) {
> +		ret = remap_pfn_range(vma, vma->vm_start,
> +				      pfn + off,
> +				      user_count << PAGE_SHIFT,
> +				      vma->vm_page_prot);
>  	}
>  #endif	/* CONFIG_MMU */
>  
> @@ -444,13 +416,16 @@ EXPORT_SYMBOL(dma_mmap_writecombine);
>   */
>  void dma_free_coherent(struct device *dev, size_t size, void *cpu_addr, dma_addr_t handle)
>  {
> -	WARN_ON(irqs_disabled());
> -
>  	if (dma_release_from_coherent(dev, get_order(size), cpu_addr))
>  		return;
>  
>  	size = PAGE_ALIGN(size);
>  
> +	if (__free_from_pool(cpu_addr, size))
> +			return;
> +
> +	WARN_ON(irqs_disabled());
> +
>  	if (!arch_is_coherent())
>  		__dma_free_remap(cpu_addr, size);
>  
> @@ -726,9 +701,6 @@ EXPORT_SYMBOL(dma_set_mask);
>  
>  static int __init dma_debug_do_init(void)
>  {
> -#ifdef CONFIG_MMU
> -	arm_vmregion_create_proc("dma-mappings", &consistent_head);
> -#endif
>  	dma_debug_init(PREALLOC_DMA_DEBUG_ENTRIES);
>  	return 0;
>  }



-- 
Kind regards,
Minchan Kim

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