Re: [PATCH] small valid_swaphandles() optimization

[Hugh Dickins <hugh@veritas.com>]

On Wed, 25 May 2005, Marcelo Tosatti wrote:
> 
> The following patch, relative to valid_swaphandles(), moves the EOF 
> check outside validity check loop, saving a few instructions. 

But increasing the function's footprint - though not very excitingly
either way.  Any benchmarks in support of it ?-)

Hmmm.  Doesn't it go wrong on the toff == swapdev->max - 1 case,
when i becomes 0 then is decremented negative at the end of the loop?
Easily fixed, but suggests your optimization not worth the obfuscation?

Hugh

> --- a/mm/swapfile.c.orig	2005-05-25 15:45:18.000000000 -0300
> +++ b/mm/swapfile.c	2005-05-25 16:20:45.000000000 -0300
> @@ -1713,11 +1713,12 @@
>  		toff++, i--;
>  	*offset = toff;
>  
> +	/* Don't read-ahead past the end of the swap area */
> +	if (toff+i >= swapdev->max)
> +		i = swapdev->max - toff - 1;
> +
>  	swap_device_lock(swapdev);
>  	do {
> -		/* Don't read-ahead past the end of the swap area */
> -		if (toff >= swapdev->max)
> -			break;
>  		/* Don't read in free or bad pages */
>  		if (!swapdev->swap_map[toff])
>  			break;
--
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