linux-kernel - Re: [PATCH] ARM: mm: clean-up in order to reduce to call kmap_high

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Message-ID: <alpine.LFD.2.03.1303052221010.28820@syhkavp.arg>
Date:	Tue, 5 Mar 2013 22:23:26 +0800 (HKT)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
cc:	Russell King <linux@....linux.org.uk>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: mm: clean-up in order to reduce to call
 kmap_high_get()

On Mon, 4 Mar 2013, Joonsoo Kim wrote:

> In kmap_atomic(), kmap_high_get() is invoked for checking already
> mapped area. In __flush_dcache_page() and dma_cache_maint_page(),
> we explicitly call kmap_high_get() before kmap_atomic()
> when cache_is_vipt(), so kmap_high_get() can be invoked twice.
> This is useless operation, so remove one.
> 
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>

Acked-by: Nicolas Pitre <nico@...aro.org>

> diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
> index c7e3759..b7711be 100644
> --- a/arch/arm/mm/dma-mapping.c
> +++ b/arch/arm/mm/dma-mapping.c
> @@ -822,16 +822,16 @@ static void dma_cache_maint_page(struct page *page, unsigned long offset,
>  		if (PageHighMem(page)) {
>  			if (len + offset > PAGE_SIZE)
>  				len = PAGE_SIZE - offset;
> -			vaddr = kmap_high_get(page);
> -			if (vaddr) {
> -				vaddr += offset;
> -				op(vaddr, len, dir);
> -				kunmap_high(page);
> -			} else if (cache_is_vipt()) {
> -				/* unmapped pages might still be cached */
> +			if (cache_is_vipt()) {
>  				vaddr = kmap_atomic(page);
>  				op(vaddr + offset, len, dir);
>  				kunmap_atomic(vaddr);
> +			} else {
> +				vaddr = kmap_high_get(page);
> +				if (vaddr) {
> +					op(vaddr + offset, len, dir);
> +					kunmap_high(page);
> +				}
>  			}
>  		} else {
>  			vaddr = page_address(page) + offset;
> diff --git a/arch/arm/mm/flush.c b/arch/arm/mm/flush.c
> index 1c8f7f5..e6a03d0 100644
> --- a/arch/arm/mm/flush.c
> +++ b/arch/arm/mm/flush.c
> @@ -170,15 +170,18 @@ void __flush_dcache_page(struct address_space *mapping, struct page *page)
>  	if (!PageHighMem(page)) {
>  		__cpuc_flush_dcache_area(page_address(page), PAGE_SIZE);
>  	} else {
> -		void *addr = kmap_high_get(page);
> -		if (addr) {
> -			__cpuc_flush_dcache_area(addr, PAGE_SIZE);
> -			kunmap_high(page);
> -		} else if (cache_is_vipt()) {
> -			/* unmapped pages might still be cached */
> +		void *addr;
> +
> +		if (cache_is_vipt()) {
>  			addr = kmap_atomic(page);
>  			__cpuc_flush_dcache_area(addr, PAGE_SIZE);
>  			kunmap_atomic(addr);
> +		} else {
> +			addr = kmap_high_get(page);
> +			if (addr) {
> +				__cpuc_flush_dcache_area(addr, PAGE_SIZE);
> +				kunmap_high(page);
> +			}
>  		}
>  	}
>  
> -- 
> 1.7.9.5
> 
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