On Tue, Sep 01, 2009 at 02:44:55PM -0400, Christoph Hellwig wrote: > On Tue, Sep 01, 2009 at 08:38:55PM +0200, Peter Zijlstra wrote: > > Do we really need a tunable for this? > > It will make increasing it in the field a lot easier. And having deal > with really large systems I have the fear that there are I/O topologies > outhere for which every "reasonable" value is too low. > > > I guess we need a limit to avoid it writing out everything, but can't we > > have something automagic? > > Some automatic adjustment would be nice. But finding the right auto > tuning will be an interesting exercise. The fact that limit is on a per-inode basis is part of the problem. Right now, we are only writing out X pages per inode, so depending on whether we have one really gargantuan inode that needs writout, or ten big inodes which are dirty, or million small inodes, the fact that we are imposing a limit based the number of pages in a single inode that we will write out seems like the wrong design choice. So perhaps the best argument for not making this be a tunable is that in the long run, we will need to put in a better algorithm for controlling how much writeback we want to do before we start saturating RAID arrays, and in that new algorithm this tunable may no longer make sense. Fine; at that point, we can make it go away. For now, though, it seems to be the best way to tweak what is going on, since I doubt we'll be able to come up with one magic number that will satisfy everyone. - Ted -- 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
