On Fri, Jul 06, 2007 at 12:26:23PM +0200, Jörn Engel wrote: > On Fri, 6 July 2007 20:01:10 +1000, David Chinner wrote: > > On Fri, Jul 06, 2007 at 04:26:51AM +0200, Nick Piggin wrote: > > > > > > Keep in mind that the way to get the most out of this meeting is for the > > > fs people to have topics of the form "we'd really like to do X, can we > > > get some help from the VM"? Or vice versa from vm people. > > > > *nod* > > > > But, surprisingly enough, the above work is relevent to this forum because > > of two things: > > > > - we've had to move to direct I/O and user space caching to work > > around deficiencies in kernel block device caching under memory > > pressure.... > > > > - we've exploited techniques that XFS supports but the VM does not. > > i.e. priority tagging of cached metadata so that less important > > metadata is tossed first (e.g. toss tree leaves before nodes and nodes > > before roots) when under memory pressure. > > And the latter is exactly what logfs needs as well. You certainly have me > interested. > > I believe it applies to btrfs and any other cow-fs as well. The point is > that higher levels get dirtied by writing lower layers. So perfect > behaviour for sync is to write leaves first, then nodes, then the root. Any > other order will either cause sync not to sync or cause unnecessary writes > and cost performance. Hmmm - I guess you could use it for writeback ordering. I hadn't really thought about that. Doesn't seem a particularly efficient way of doing it, though. Why not just use multiple address spaces for this? i.e. one per level and flush in ascending order. 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
