Re: [PATCH] ION: Sys_heap: Makes ion buffer always alloc from page pool

[Laura Abbott]

On 05/04/2016 08:27 PM, Chen Feng wrote:
> Makes the ion buffer always alloced from page pool, no matter
> it's cached or not. In this way, it can improve the efficiency
> of it.
>
> Currently, there is no difference from cached or non-cached buffer
> for the page pool.


The advantage of the uncached pool was that the pages in the pool
were always clean in the cache. This is lost here with the addition
of cached pages to the same pool as uncached pages I agree the
cache path could benefit from pooling but we need to keep the caching
model consistent.

> Signed-off-by: Chen Feng <puck.chen@xxxxxxxxxxxxx>
> ---
>  drivers/staging/android/ion/ion_system_heap.c | 19 ++-----------------
>  1 file changed, 2 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/staging/android/ion/ion_system_heap.c b/drivers/staging/android/ion/ion_system_heap.c
> index b69dfc7..caf11fc 100644
> --- a/drivers/staging/android/ion/ion_system_heap.c
> +++ b/drivers/staging/android/ion/ion_system_heap.c
> @@ -56,24 +56,10 @@ static struct page *alloc_buffer_page(struct ion_system_heap *heap,
>  				      struct ion_buffer *buffer,
>  				      unsigned long order)
>  {
> -	bool cached = ion_buffer_cached(buffer);
>  	struct ion_page_pool *pool = heap->pools[order_to_index(order)];
>  	struct page *page;
>
> -	if (!cached) {
> -		page = ion_page_pool_alloc(pool);
> -	} else {
> -		gfp_t gfp_flags = low_order_gfp_flags;
> -
> -		if (order > 4)
> -			gfp_flags = high_order_gfp_flags;
> -		page = alloc_pages(gfp_flags | __GFP_COMP, order);
> -		if (!page)
> -			return NULL;
> -		ion_pages_sync_for_device(NULL, page, PAGE_SIZE << order,
> -						DMA_BIDIRECTIONAL);
> -	}
> -
> +	page = ion_page_pool_alloc(pool);
>  	return page;
>  }
>
> @@ -81,9 +67,8 @@ static void free_buffer_page(struct ion_system_heap *heap,
>  			     struct ion_buffer *buffer, struct page *page)
>  {
>  	unsigned int order = compound_order(page);
> -	bool cached = ion_buffer_cached(buffer);
>
> -	if (!cached && !(buffer->private_flags & ION_PRIV_FLAG_SHRINKER_FREE)) {
> +	if (!(buffer->private_flags & ION_PRIV_FLAG_SHRINKER_FREE)) {
>  		struct ion_page_pool *pool = heap->pools[order_to_index(order)];
>
>  		ion_page_pool_free(pool, page);