Re: [PATCH] mm: don't cap request size based on read-ahead setting

[Hillf Danton]

On Wednesday, November 16, 2016 12:31 PM Jens Axboe wrote:
> @@ -369,10 +369,25 @@ ondemand_readahead(struct address_space *mapping,
>   		   bool hit_readahead_marker, pgoff_t offset,
>   		   unsigned long req_size)
>   {
> -	unsigned long max = ra->ra_pages;
> +	unsigned long io_pages, max_pages;
>   	pgoff_t prev_offset;
> 
>   	/*
> +	 * If bdi->io_pages is set, that indicates the (soft) max IO size
> +	 * per command for that device. If we have that available, use
> +	 * that as the max suitable read-ahead size for this IO. Instead of
> +	 * capping read-ahead at ra_pages if req_size is larger, we can go
> +	 * up to io_pages. If io_pages isn't set, fall back to using
> +	 * ra_pages as a safe max.
> +	 */
> +	io_pages = inode_to_bdi(mapping->host)->io_pages;
> +	if (io_pages) {
> +		max_pages = max_t(unsigned long, ra->ra_pages, req_size);
> +		io_pages = min(io_pages, max_pages);

Doubt if you mean
		max_pages = min(io_pages, max_pages);
> +	} else
> +		max_pages = ra->ra_pages;
> +