Hi!
Recent changes to ioremap and unification of vmalloc regions on ARM significantly reduces the possible size of the consistent dma region and limited allowed dma coherent/writecombine allocations.
This experimental patch series replaces custom consistent dma regions usage in dma-mapping framework in favour of generic vmalloc areas created on demand for each coherent and writecombine allocations.
This patch is based on vanilla v3.4-rc2 release.
Best regards Marek Szyprowski Samsung Poland R&D Center
Patch summary:
Marek Szyprowski (4): mm: vmalloc: use const void * for caller argument mm: vmalloc: export find_vm_area() function mm: vmalloc: add VM_DMA flag to indicate areas used by dma-mapping framework ARM: remove consistent dma region and use common vmalloc range for dma allocations
arch/arm/include/asm/dma-mapping.h | 2 +- arch/arm/mm/dma-mapping.c | 220 +++++++----------------------------- include/linux/vmalloc.h | 10 +- mm/vmalloc.c | 31 ++++-- 4 files changed, 67 insertions(+), 196 deletions(-)
'const void *' is a safer type for caller function type. This patch updates all references to caller function type.
Signed-off-by: Marek Szyprowski m.szyprowski@samsung.com Reviewed-by: Kyungmin Park kyungmin.park@samsung.com --- include/linux/vmalloc.h | 8 ++++---- mm/vmalloc.c | 18 +++++++++--------- 2 files changed, 13 insertions(+), 13 deletions(-)
diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h index dcdfc2b..2e28f4d 100644 --- a/include/linux/vmalloc.h +++ b/include/linux/vmalloc.h @@ -32,7 +32,7 @@ struct vm_struct { struct page **pages; unsigned int nr_pages; phys_addr_t phys_addr; - void *caller; + const void *caller; };
/* @@ -62,7 +62,7 @@ extern void *vmalloc_32_user(unsigned long size); extern void *__vmalloc(unsigned long size, gfp_t gfp_mask, pgprot_t prot); extern void *__vmalloc_node_range(unsigned long size, unsigned long align, unsigned long start, unsigned long end, gfp_t gfp_mask, - pgprot_t prot, int node, void *caller); + pgprot_t prot, int node, const void *caller); extern void vfree(const void *addr);
extern void *vmap(struct page **pages, unsigned int count, @@ -85,13 +85,13 @@ static inline size_t get_vm_area_size(const struct vm_struct *area)
extern struct vm_struct *get_vm_area(unsigned long size, unsigned long flags); extern struct vm_struct *get_vm_area_caller(unsigned long size, - unsigned long flags, void *caller); + unsigned long flags, const void *caller); extern struct vm_struct *__get_vm_area(unsigned long size, unsigned long flags, unsigned long start, unsigned long end); extern struct vm_struct *__get_vm_area_caller(unsigned long size, unsigned long flags, unsigned long start, unsigned long end, - void *caller); + const void *caller); extern struct vm_struct *remove_vm_area(const void *addr);
extern int map_vm_area(struct vm_struct *area, pgprot_t prot, diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 94dff88..8bc7f3e 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -1279,7 +1279,7 @@ DEFINE_RWLOCK(vmlist_lock); struct vm_struct *vmlist;
static void setup_vmalloc_vm(struct vm_struct *vm, struct vmap_area *va, - unsigned long flags, void *caller) + unsigned long flags, const void *caller) { vm->flags = flags; vm->addr = (void *)va->va_start; @@ -1305,7 +1305,7 @@ static void insert_vmalloc_vmlist(struct vm_struct *vm) }
static void insert_vmalloc_vm(struct vm_struct *vm, struct vmap_area *va, - unsigned long flags, void *caller) + unsigned long flags, const void *caller) { setup_vmalloc_vm(vm, va, flags, caller); insert_vmalloc_vmlist(vm); @@ -1313,7 +1313,7 @@ static void insert_vmalloc_vm(struct vm_struct *vm, struct vmap_area *va,
static struct vm_struct *__get_vm_area_node(unsigned long size, unsigned long align, unsigned long flags, unsigned long start, - unsigned long end, int node, gfp_t gfp_mask, void *caller) + unsigned long end, int node, gfp_t gfp_mask, const void *caller) { struct vmap_area *va; struct vm_struct *area; @@ -1374,7 +1374,7 @@ EXPORT_SYMBOL_GPL(__get_vm_area);
struct vm_struct *__get_vm_area_caller(unsigned long size, unsigned long flags, unsigned long start, unsigned long end, - void *caller) + const void *caller) { return __get_vm_area_node(size, 1, flags, start, end, -1, GFP_KERNEL, caller); @@ -1396,7 +1396,7 @@ struct vm_struct *get_vm_area(unsigned long size, unsigned long flags) }
struct vm_struct *get_vm_area_caller(unsigned long size, unsigned long flags, - void *caller) + const void *caller) { return __get_vm_area_node(size, 1, flags, VMALLOC_START, VMALLOC_END, -1, GFP_KERNEL, caller); @@ -1567,9 +1567,9 @@ EXPORT_SYMBOL(vmap);
static void *__vmalloc_node(unsigned long size, unsigned long align, gfp_t gfp_mask, pgprot_t prot, - int node, void *caller); + int node, const void *caller); static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask, - pgprot_t prot, int node, void *caller) + pgprot_t prot, int node, const void *caller) { const int order = 0; struct page **pages; @@ -1642,7 +1642,7 @@ fail: */ void *__vmalloc_node_range(unsigned long size, unsigned long align, unsigned long start, unsigned long end, gfp_t gfp_mask, - pgprot_t prot, int node, void *caller) + pgprot_t prot, int node, const void *caller) { struct vm_struct *area; void *addr; @@ -1698,7 +1698,7 @@ fail: */ static void *__vmalloc_node(unsigned long size, unsigned long align, gfp_t gfp_mask, pgprot_t prot, - int node, void *caller) + int node, const void *caller) { return __vmalloc_node_range(size, align, VMALLOC_START, VMALLOC_END, gfp_mask, prot, node, caller);
find_vm_area() function is usefull for other core subsystems (like dma-mapping) to get access to vm_area internals.
Signed-off-by: Marek Szyprowski m.szyprowski@samsung.com Reviewed-by: Kyungmin Park kyungmin.park@samsung.com --- include/linux/vmalloc.h | 1 + mm/vmalloc.c | 10 +++++++++- 2 files changed, 10 insertions(+), 1 deletions(-)
diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h index 2e28f4d..6071e91 100644 --- a/include/linux/vmalloc.h +++ b/include/linux/vmalloc.h @@ -93,6 +93,7 @@ extern struct vm_struct *__get_vm_area_caller(unsigned long size, unsigned long start, unsigned long end, const void *caller); extern struct vm_struct *remove_vm_area(const void *addr); +extern struct vm_struct *find_vm_area(const void *addr);
extern int map_vm_area(struct vm_struct *area, pgprot_t prot, struct page ***pages); diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 8bc7f3e..8cb7f22 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -1402,7 +1402,15 @@ struct vm_struct *get_vm_area_caller(unsigned long size, unsigned long flags, -1, GFP_KERNEL, caller); }
-static struct vm_struct *find_vm_area(const void *addr) +/** + * find_vm_area - find a continuous kernel virtual area + * @addr: base address + * + * Search for the kernel VM area starting at @addr, and return it. + * It is up to the caller to do all required locking to keep the returned + * pointer valid. + */ +struct vm_struct *find_vm_area(const void *addr) { struct vmap_area *va;
Add new type of vm_area intented to be used for consisten mappings created by dma-mapping framework.
Signed-off-by: Marek Szyprowski m.szyprowski@samsung.com Reviewed-by: Kyungmin Park kyungmin.park@samsung.com --- include/linux/vmalloc.h | 1 + mm/vmalloc.c | 3 +++ 2 files changed, 4 insertions(+), 0 deletions(-)
diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h index 6071e91..8a9555a 100644 --- a/include/linux/vmalloc.h +++ b/include/linux/vmalloc.h @@ -14,6 +14,7 @@ struct vm_area_struct; /* vma defining user mapping in mm_types.h */ #define VM_USERMAP 0x00000008 /* suitable for remap_vmalloc_range */ #define VM_VPAGES 0x00000010 /* buffer for pages was vmalloc'ed */ #define VM_UNLIST 0x00000020 /* vm_struct is not listed in vmlist */ +#define VM_DMA 0x00000040 /* used by dma-mapping framework */ /* bits [20..32] reserved for arch specific ioremap internals */
/* diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 8cb7f22..9c13bab 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -2582,6 +2582,9 @@ static int s_show(struct seq_file *m, void *p) if (v->flags & VM_IOREMAP) seq_printf(m, " ioremap");
+ if (v->flags & VM_DMA) + seq_printf(m, " dma"); + if (v->flags & VM_ALLOC) seq_printf(m, " vmalloc");
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.
Signed-off-by: Marek Szyprowski m.szyprowski@samsung.com Reviewed-by: Kyungmin Park kyungmin.park@samsung.com --- arch/arm/include/asm/dma-mapping.h | 2 +- arch/arm/mm/dma-mapping.c | 220 +++++++----------------------------- 2 files changed, 40 insertions(+), 182 deletions(-)
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..74ff839 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/vmalloc.h> +#include <linux/io.h>
#include <asm/memory.h> #include <asm/highmem.h> @@ -119,204 +121,59 @@ 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; - - if (!consistent_pte) { - printk(KERN_ERR "%s: 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. - */ - bit = fls(size - 1); - if (bit > SECTION_SHIFT) - bit = SECTION_SHIFT; - align = 1 << bit; - - /* - * 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(); + struct vm_struct *area; + unsigned long addr;
- return (void *)c->vm_start; - } - return NULL; + area = get_vm_area_caller(size, VM_DMA | VM_USERMAP, caller); + 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 arm_vmregion *c; - unsigned long addr; - pte_t *ptep; - int idx; - u32 off; + struct vm_struct *area; + + read_lock(&vmlist_lock);
- c = arm_vmregion_find_remove(&consistent_head, (unsigned long)cpu_addr); - if (!c) { + area = find_vm_area(cpu_addr); + if (!area) { printk(KERN_ERR "%s: trying to free invalid coherent area: %p\n", __func__, cpu_addr); dump_stack(); + read_unlock(&vmlist_lock); return; }
- if ((c->vm_end - c->vm_start) != size) { + /* + * get_vm_area_caller always use additional guard page, so skip it here + */ + if (area->size - PAGE_SIZE != size) { printk(KERN_ERR "%s: freeing wrong coherent size (%ld != %d)\n", - __func__, c->vm_end - c->vm_start, size); + __func__, area->size, size); dump_stack(); - size = c->vm_end - c->vm_start; + size = area->size; }
- 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); - - 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); + unmap_kernel_range((unsigned long)cpu_addr, size); + read_unlock(&vmlist_lock);
- flush_tlb_kernel_range(c->vm_start, c->vm_end); - - arm_vmregion_free(&consistent_head, c); + vunmap(cpu_addr); }
#else /* !CONFIG_MMU */ @@ -398,25 +255,29 @@ static int dma_mmap(struct device *dev, struct vm_area_struct *vma, { int ret = -ENXIO; #ifdef CONFIG_MMU + struct vm_struct *area; unsigned long user_size, kern_size; - struct arm_vmregion *c;
+ read_lock(&vmlist_lock); + area = find_vm_area(cpu_addr); user_size = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
- c = arm_vmregion_find(&consistent_head, (unsigned long)cpu_addr); - if (c) { + if (area) { unsigned long off = vma->vm_pgoff; + unsigned long phys = __phys_to_pfn(area->phys_addr);
- kern_size = (c->vm_end - c->vm_start) >> PAGE_SHIFT; + /* skip vmalloc guard page */ + kern_size = (area->size >> PAGE_SHIFT) - 1;
if (off < kern_size && user_size <= (kern_size - off)) { ret = remap_pfn_range(vma, vma->vm_start, - page_to_pfn(c->vm_pages) + off, + phys + off, user_size << PAGE_SHIFT, vma->vm_page_prot); } } + read_unlock(&vmlist_lock); #endif /* CONFIG_MMU */
return ret; @@ -726,9 +587,6 @@ 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; }
On Fri, Apr 13, 2012 at 04:05:50PM +0200, 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.
NAK. I don't think you appreciate the contexts from which the dma coherent code can be called from, and the reason why we pre-allocate the page tables (so that IRQ-based allocations work.)
The vmalloc region doesn't allow that because page tables are allocated using GFP_KERNEL not GFP_ATOMIC.
Sorry.
On 04/14/2012 03:38 AM, Russell King - ARM Linux wrote:
On Fri, Apr 13, 2012 at 04:05:50PM +0200, 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.
NAK. I don't think you appreciate the contexts from which the dma coherent code can be called from, and the reason why we pre-allocate the page tables (so that IRQ-based allocations work.)
The vmalloc region doesn't allow that because page tables are allocated using GFP_KERNEL not GFP_ATOMIC.
Sorry.
Off-topic.
I don't know why vmalloc functions have gfp_t argument. As Russel pointed out, we allocates page tables with GFP_KERNEL regardless of gfp_t passed. It means gfp_t passed is useless. I see there are many cases calling __vmalloc with GFP_NOFS, even GFP_ATOMIC. Then, it could end up deadlocking in reclaim context or schedule bug. I'm not sure why we can't see such bugs until now. If I didn't miss something, Shouldn't we fix it?
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(4/15/12 9:32 PM), Minchan Kim wrote:
On 04/14/2012 03:38 AM, Russell King - ARM Linux wrote:
On Fri, Apr 13, 2012 at 04:05:50PM +0200, 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.
NAK. I don't think you appreciate the contexts from which the dma coherent code can be called from, and the reason why we pre-allocate the page tables (so that IRQ-based allocations work.)
The vmalloc region doesn't allow that because page tables are allocated using GFP_KERNEL not GFP_ATOMIC.
Sorry.
Off-topic.
I don't know why vmalloc functions have gfp_t argument. As Russel pointed out, we allocates page tables with GFP_KERNEL regardless of gfp_t passed. It means gfp_t passed is useless. I see there are many cases calling __vmalloc with GFP_NOFS, even GFP_ATOMIC. Then, it could end up deadlocking in reclaim context or schedule bug. I'm not sure why we can't see such bugs until now. If I didn't miss something, Shouldn't we fix it?
I believe it should be fixed. of course. :)
Hi,
I see a bottle-neck with the current dma-mapping framework. Issue seems to be with the Virtual memory allocation for access in kernel address space.
1. In "arch/arm/mm/dma-mapping.c" there is a initialization call to "consistent_init". It reserves size 32MB of Kernel Address space. 2. "consistent_init" allocates memory for kernel page directory and page tables.
3. "__iommu_alloc_remap" function allocates virtual memory region in kernel address space reserved in step 1.
4. "__iommu_alloc_remap" function then maps the allocated pages to the address space reserved in step 3.
Since the virtual memory area allocated for mapping these pages in kernel address space is only 32MB,
eventually the calls for allocation and mapping new pages into kernel address space are going to fail once 32 MB is exhausted.
e.g., For Exynos 5 platform Each framebuffer for 1280x800 resolution consumes around 4MB.
We have a scenario where X11 DRI driver would allocate Non-contig pages for all "Pixmaps" through arm_iommu_alloc_attrs" function which will follow the path given above in steps 1 - 4.
Now the problem is the size limitation of 32MB. We may want to allocate more than 8 such buffers when X11 DRI driver is integrated. Possible solutions:
1. Why do we need to create a kernel virtual address space? Are we going to access these pages in kernel using this address?
If we are not going to access anything in kernel then why do we need to map these pages in kernel address space?. If we can avoid this then the problem can be solved.
OR
2 Is it used for only book-keeping to retrieve "struct pages" later on for passing/mapping to different devices?
If yes, then we have to find another way.
For "dmabuf" framework one solution could be to add a new member variable "pages" in the exporting driver's local object and use that for passing/mapping to different devices.
Moreover, even if we increase to say 64 MB that would not be enough for our use, we never know how many graphic applications would be spawned by the user. Let me know your opinion on this.
Regards, Abhinav
On Fri, Apr 13, 2012 at 11:05 PM, Marek Szyprowski <m.szyprowski@samsung.com
wrote:
Hi!
Recent changes to ioremap and unification of vmalloc regions on ARM significantly reduces the possible size of the consistent dma region and limited allowed dma coherent/writecombine allocations.
This experimental patch series replaces custom consistent dma regions usage in dma-mapping framework in favour of generic vmalloc areas created on demand for each coherent and writecombine allocations.
This patch is based on vanilla v3.4-rc2 release.
Best regards Marek Szyprowski Samsung Poland R&D Center
Patch summary:
Marek Szyprowski (4): mm: vmalloc: use const void * for caller argument mm: vmalloc: export find_vm_area() function mm: vmalloc: add VM_DMA flag to indicate areas used by dma-mapping framework ARM: remove consistent dma region and use common vmalloc range for dma allocations
arch/arm/include/asm/dma-mapping.h | 2 +- arch/arm/mm/dma-mapping.c | 220 +++++++----------------------------- include/linux/vmalloc.h | 10 +- mm/vmalloc.c | 31 ++++-- 4 files changed, 67 insertions(+), 196 deletions(-)
-- 1.7.1.569.g6f426
Linaro-mm-sig mailing list Linaro-mm-sig@lists.linaro.org http://lists.linaro.org/mailman/listinfo/linaro-mm-sig
On Mon, Apr 23, 2012 at 09:02:25PM +0900, Abhinav Kochhar wrote:
Hi,
I see a bottle-neck with the current dma-mapping framework. Issue seems to be with the Virtual memory allocation for access in kernel address space.
- In "arch/arm/mm/dma-mapping.c" there is a initialization call to
"consistent_init". It reserves size 32MB of Kernel Address space. 2. "consistent_init" allocates memory for kernel page directory and page tables.
- "__iommu_alloc_remap" function allocates virtual memory region in kernel
address space reserved in step 1.
- "__iommu_alloc_remap" function then maps the allocated pages to the
address space reserved in step 3.
Since the virtual memory area allocated for mapping these pages in kernel address space is only 32MB,
eventually the calls for allocation and mapping new pages into kernel address space are going to fail once 32 MB is exhausted.
e.g., For Exynos 5 platform Each framebuffer for 1280x800 resolution consumes around 4MB.
We have a scenario where X11 DRI driver would allocate Non-contig pages for all "Pixmaps" through arm_iommu_alloc_attrs" function which will follow the path given above in steps 1 - 4.
Now the problem is the size limitation of 32MB. We may want to allocate more than 8 such buffers when X11 DRI driver is integrated. Possible solutions:
- Why do we need to create a kernel virtual address space? Are we going to
access these pages in kernel using this address?
If we are not going to access anything in kernel then why do we need to map these pages in kernel address space?. If we can avoid this then the problem can be solved.
OR
2 Is it used for only book-keeping to retrieve "struct pages" later on for passing/mapping to different devices?
If yes, then we have to find another way.
For "dmabuf" framework one solution could be to add a new member variable "pages" in the exporting driver's local object and use that for passing/mapping to different devices.
Moreover, even if we increase to say 64 MB that would not be enough for our use, we never know how many graphic applications would be spawned by the user. Let me know your opinion on this.
This is more or less the reason I'm so massively opposed to adding vmap to dma-buf - you _really_ burn through the vmap space ridiculously quickly on 32bit platforms with too much memory (i.e. everything with more than 1 G).
You need to map/unmap everything page-by-page with all the usual kmap apis the kernel provides. -Daniel
linaro-mm-sig@lists.linaro.org
-
Abhinav Kochhar -
Daniel Vetter -
KOSAKI Motohiro -
Marek Szyprowski -
Minchan Kim -
Russell King - ARM Linux