ion: optimize ion_heap_buffer_zero

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/android/ion/ion_heap.c b/drivers/staging/android/ion/ion_heap.c
index 0a5cea0..ce31561 100644 (file)
--- 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;
 }