Try to start writeback if none underway
int try_to_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
the reason of writeback
Invoke writeback_inodes_sb_nr if no writeback is currently underway. Returns 1 if writeback was started, 0 if not.