page_cache_sync_readahead — generic file readahead
void page_cache_sync_readahead
(struct address_space * mapping, struct file_ra_state * ra, struct file * filp, pgoff_t offset, unsigned long req_size);
address_space which holds the pagecache and I/O vectors
file_ra_state which holds the readahead state
passed on to ->readpage and ->readpages
start offset into mapping, in pagecache page-sized units
hint: total size of the read which the caller is performing in pagecache pages
page_cache_sync_readahead should be called when a cache miss happened: it will submit the read. The readahead logic may decide to piggyback more pages onto the read request if access patterns suggest it will improve performance.