When JFS decides to drop a dirty metapage, it simply clears the META_dirty
bit and leave alone the PG_dirty and PAGECACHE_TAG_DIRTY bits.

When such no-write page goes to metapage_writepage(), the `relic'
PAGECACHE_TAG_DIRTY tag should be cleared, to prevent pdflush from
repeatedly trying to sync them.  This is done through
set_page_writeback(), so call it should be called in all cases.  If
no I/O is initiated, end_page_writeback() should be called immediately.

This is how __block_write_full_page() does things.
Signed-off-by: Dave Kleikamp <shaggy@linux.vnet.ibm.com>
CC: Fengguang Wu <wfg@mail.ustc.edu.cn>