On Tue, Jan 15, 2008 at 08:36:46PM +0800, Fengguang Wu wrote: > Redirtied inodes could be seen in really fast writes. > They should really be synced as soon as possible. > > redirty_tail() could delay the inode for up to 30s. > Kill the delay by using requeue_io() instead. That's actually bad for anything that does delayed allocation or updates state on data I/o completion. e.g. XFS when writing past EOF doing delalloc dirties the inode during writeout (allocation) and then updates the file size on data I/o completion hence dirtying the inode again. With this change, writing the last pages out would result in hitting this code and causing the inode to be flushed very soon after the data write. Then, after the inode write is issued, we get data I/o completion which dirties the inode again, resulting in needing to write the inode again to clean it. i.e. it introduces a potential new and useless inode write I/O. Also, the immediate inode write may be useless for XFS because the inode may be pinned in memory due to async transactions still in flight (e.g. from delalloc) so we've got two situations where flushing the inode immediately is suboptimal. Hence I don't think this is an optimisation that should be made in the generic writeback code. Cheers, Dave. -- Dave Chinner Principal Engineer SGI Australian Software Group - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
