Re: [PATCH] mm: do not consider SWAP to calculate available when not necessary

[Matthew Wilcox]

On Mon, Nov 26, 2018 at 07:58:23AM +0800, Yang Yang wrote:
> When si_mem_available() calculates 'available', it takes SWAP
> into account. But if CONFIG_SWAP is N or SWAP is off(some embedded system
> would like to do that), there is no need to consider it.

I don't understand this patch.  The pagecache can be written back to
storage if it is dirty, regardless of whether there is swap space.

> @@ -4724,9 +4726,13 @@ long si_mem_available(void)
>  	 * Not all the page cache can be freed, otherwise the system will
>  	 * start swapping. Assume at least half of the page cache, or the
>  	 * low watermark worth of cache, needs to stay.
> +	 * But if CONFIG_SWAP is N or SWAP is off, do not consider it.
>  	 */
>  	pagecache = pages[LRU_ACTIVE_FILE] + pages[LRU_INACTIVE_FILE];
> -	pagecache -= min(pagecache / 2, wmark_low);
> +#ifdef CONFIG_SWAP
> +	if (i.totalswap > 0)
> +		pagecache -= min(pagecache / 2, wmark_low);
> +#endif
>  	available += pagecache;
>  
>  	/*
> -- 
> 2.15.2
>