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Subject[PATCH 101/115] ion: optimize ion_heap_buffer_zero
Date
From: Colin Cross <ccross@android.com>

ion_heap_buffer_zero can spend a long time in unmap_kernel_range
if it has to broadcast a tlb flush to every cpu for every page.
Modify it to batch pages into a larger region to clear using a
single mapping. This may cause the mapping size to change if
the buffer size is not a multiple of the mapping size, so
switch to allocating the address space for each chunk. This
allows us to use vm_map_ram to handle the allocation and mapping
together.

The number of pages to zero using a single mapping is set to 32
to hit the fastpath in vm_map_ram.

Signed-off-by: Colin Cross <ccross@android.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
---
drivers/staging/android/ion/ion_heap.c | 36 +++++++++++++++++++++-------------
1 file changed, 22 insertions(+), 14 deletions(-)

diff --git a/drivers/staging/android/ion/ion_heap.c b/drivers/staging/android/ion/ion_heap.c
index 0a5cea0..ce31561 100644
--- a/drivers/staging/android/ion/ion_heap.c
+++ b/drivers/staging/android/ion/ion_heap.c
@@ -100,40 +100,48 @@ int ion_heap_map_user(struct ion_heap *heap, struct ion_buffer *buffer,
return 0;
}

+static int ion_heap_clear_pages(struct page **pages, int num, pgprot_t pgprot)
+{
+ void *addr = vm_map_ram(pages, num, -1, pgprot);
+ if (!addr)
+ return -ENOMEM;
+ memset(addr, 0, PAGE_SIZE * num);
+ vm_unmap_ram(addr, num);
+
+ return 0;
+}
+
int ion_heap_buffer_zero(struct ion_buffer *buffer)
{
struct sg_table *table = buffer->sg_table;
pgprot_t pgprot;
struct scatterlist *sg;
- struct vm_struct *vm_struct;
int i, j, ret = 0;
+ struct page *pages[32];
+ int k = 0;

if (buffer->flags & ION_FLAG_CACHED)
pgprot = PAGE_KERNEL;
else
pgprot = pgprot_writecombine(PAGE_KERNEL);

- vm_struct = get_vm_area(PAGE_SIZE, VM_ALLOC);
- if (!vm_struct)
- return -ENOMEM;
-
for_each_sg(table->sgl, sg, table->nents, i) {
struct page *page = sg_page(sg);
unsigned long len = sg->length;

for (j = 0; j < len / PAGE_SIZE; j++) {
- struct page *sub_page = page + j;
- struct page **pages = &sub_page;
- ret = map_vm_area(vm_struct, pgprot, &pages);
- if (ret)
- goto end;
- memset(vm_struct->addr, 0, PAGE_SIZE);
- unmap_kernel_range((unsigned long)vm_struct->addr,
- PAGE_SIZE);
+ pages[k++] = page + j;
+ if (k == ARRAY_SIZE(pages)) {
+ ret = ion_heap_clear_pages(pages, k, pgprot);
+ if (ret)
+ goto end;
+ k = 0;
+ }
}
+ if (k)
+ ret = ion_heap_clear_pages(pages, k, pgprot);
}
end:
- free_vm_area(vm_struct);
return ret;
}

--
1.8.3.2


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