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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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