Man page 9 : writeback_inodes_sb_nr

writeback_inodes_sb_nr - writeback dirty inodes from given super_block

void writeback_inodes_sb_nr(struct super_block *  sb , unsigned long  nr , enum wb_reason  reason );

sb
    the superblock

nr
    the number of pages to write

reason
    reason why some writeback work initiated

Start writeback on some inodes on this super_block. No guarantees are made on how many (if any) will be written, and this function does not wait for IO completion of submitted IO.