On 11/16/2016 12:17 AM, Hillf Danton wrote:
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);
No, that is what I mean. We want the maximum of the RA setting and the user IO size, but the minimum of that and the device max command size. -- Jens Axboe
