ext4: Rework the ext4_da_writepages() function
With the below changes we reserve credit needed to insert only one extent resulting from a call to single get_block. This makes sure we don't take too much journal credits during writeout. We also don't limit the pages to write. That means we loop through the dirty pages building largest possible contiguous block request. Then we issue a single get_block request. We may get less block that we requested. If so we would end up not mapping some of the buffer_heads. That means those buffer_heads are still marked delay. Later in the writepage callback via __mpage_writepage we redirty those pages. We should also not limit/throttle wbc->nr_to_write in the filesystem writepages callback. That cause wrong behaviour in generic_sync_sb_inodes caused by wbc->nr_to_write being <= 0 Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com> Reviewed-by: Mingming Cao <cmm@us.ibm.com> Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
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