linux-kernel - Re: [RESEND PATCH] ION: Sys_heap: Add cached pool to spead up cached buffer alloc

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Date:	Mon, 9 May 2016 16:50:31 -0700
From:	Laura Abbott <labbott@...hat.com>
To:	Chen Feng <puck.chen@...ilicon.com>, saberlily.xia@...ilicon.com,
	gregkh@...uxfoundation.org, arve@...roid.com,
	riandrews@...roid.com, paul.gortmaker@...driver.com,
	bmarsh94@...il.com, devel@...verdev.osuosl.org,
	linux-kernel@...r.kernel.org
Cc:	xuyiping@...ilicon.com, suzhuangluan@...ilicon.com,
	dan.zhao@...ilicon.com, linuxarm@...wei.com, puck.chen@...mail.com
Subject: Re: [RESEND PATCH] ION: Sys_heap: Add cached pool to spead up cached
 buffer alloc

On 05/09/2016 01:37 AM, Chen Feng wrote:
> Add ion cached pool in system heap.
>
> Signed-off-by: Chen Feng <puck.chen@...ilicon.com>
> Signed-off-by: Xia  Qing <saberlily.xia@...ilicon.com>
> Reviewed-by: Fu Jun <oliver.fu@...ilicon.com>
> ---
>  drivers/staging/android/ion/ion_system_heap.c | 145 +++++++++++++++++---------
>  1 file changed, 95 insertions(+), 50 deletions(-)
>
> diff --git a/drivers/staging/android/ion/ion_system_heap.c b/drivers/staging/android/ion/ion_system_heap.c
> index b69dfc7..c633252 100644
> --- a/drivers/staging/android/ion/ion_system_heap.c
> +++ b/drivers/staging/android/ion/ion_system_heap.c
> @@ -49,7 +49,8 @@ static inline unsigned int order_to_size(int order)
>
>  struct ion_system_heap {
>  	struct ion_heap heap;
> -	struct ion_page_pool *pools[0];
> +	struct ion_page_pool *uncached_pools[0];
> +	struct ion_page_pool *cached_pools[0];
>  };
>
>  static struct page *alloc_buffer_page(struct ion_system_heap *heap,
> @@ -57,39 +58,36 @@ static struct page *alloc_buffer_page(struct ion_system_heap *heap,
>  				      unsigned long order)
>  {
>  	bool cached = ion_buffer_cached(buffer);
> -	struct ion_page_pool *pool = heap->pools[order_to_index(order)];
> +	struct ion_page_pool *pool;
>  	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);
> -	}
> +	if (!cached)
> +		pool = heap->uncached_pools[order_to_index(order)];
> +	else
> +		pool = heap->cached_pools[order_to_index(order)];
>
> +	page = ion_page_pool_alloc(pool);
>  	return page;
>  }
>

This is a change in behavior. The page is no longer guaranteed to be synced
in the cache. If the page came from the pool (not just freshly allocated)
the cache state is unknown. Do you have a good explanation why we no longer
need to do the cache flush here on every allocation?

Thanks,
Laura