-/**
- * mpage_readpages - populate an address space with some pages, and
- * start reads against them.
- *
- * @mapping: the address_space
- * @pages: The address of a list_head which contains the target pages. These
- * pages have their ->index populated and are otherwise uninitialised.
- *
- * The page at @pages->prev has the lowest file offset, and reads should be
- * issued in @pages->prev to @pages->next order.
- *
- * @nr_pages: The number of pages at *@pages
- * @get_block: The filesystem's block mapper function.
- *
- * This function walks the pages and the blocks within each page, building and
- * emitting large BIOs.
- *
- * If anything unusual happens, such as:
- *
- * - encountering a page which has buffers
- * - encountering a page which has a non-hole after a hole
- * - encountering a page with non-contiguous blocks
- *
- * then this code just gives up and calls the buffer_head-based read function.
- * It does handle a page which has holes at the end - that is a common case:
- * the end-of-file on blocksize < PAGE_CACHE_SIZE setups.
- *
- * BH_Boundary explanation:
- *
- * There is a problem. The mpage read code assembles several pages, gets all
- * their disk mappings, and then submits them all. That's fine, but obtaining
- * the disk mappings may require I/O. Reads of indirect blocks, for example.
- *
- * So an mpage read of the first 16 blocks of an ext2 file will cause I/O to be
- * submitted in the following order:
- * 12 0 1 2 3 4 5 6 7 8 9 10 11 13 14 15 16
- * because the indirect block has to be read to get the mappings of blocks
- * 13,14,15,16. Obviously, this impacts performance.
- *
- * So what we do it to allow the filesystem's get_block() function to set
- * BH_Boundary when it maps block 11. BH_Boundary says: mapping of the block
- * after this one will require I/O against a block which is probably close to
- * this one. So you should push what I/O you have currently accumulated.
- *
- * This all causes the disk requests to be issued in the correct order.
- */