Re: [PATCH v2] mm: fix long time stall from mm_populate

[Matthew Wilcox <willy@infradead.org>]

On Mon, Mar 02, 2020 at 04:26:38PM -0800, Minchan Kim wrote:
> @@ -1196,6 +1196,7 @@ int __mm_populate(unsigned long start, unsigned long len, int ignore_errors)
>  	struct vm_area_struct *vma = NULL;
>  	int locked = 0;
>  	long ret = 0;
> +	bool tried = false;

How about ...

	int *lockedp = &locked;

>  
>  	end = start + len;
>  
> @@ -1226,14 +1227,18 @@ int __mm_populate(unsigned long start, unsigned long len, int ignore_errors)
>  		 * double checks the vma flags, so that it won't mlock pages
>  		 * if the vma was already munlocked.
>  		 */
> -		ret = populate_vma_page_range(vma, nstart, nend, &locked);
> +		ret = populate_vma_page_range(vma, nstart, nend,
> +						tried ? NULL : &locked);

		ret = populate_vma_page_range(vma, nstart, nend, lockedp);

>  		if (ret < 0) {
>  			if (ignore_errors) {
>  				ret = 0;
>  				continue;	/* continue at next VMA */
>  			}
>  			break;
> -		}
> +		} else if (ret == 0)
> +			tried = true;
> +		else
> +			tried = false;

		} else if (ret == 0)
			lockedp = NULL;

Maybe there's a better name than lockedp.