Dave Chinner wrote: > To keep on top of this, we keep adding new variations and types and > expect the filesystems to make best use of them (without > documentation) to optimise for certain situations. Example - the > new(ish) BIO_META tag that only CFQ understands. I can change the > way XFS issues bios to use this tag to make CFQ behave the same way > it used to w.r.t. metadata I/O from XFS, but then the deadline and > AS will probably regress because they don't understand that tag and > still need the old optimisations that just got removed. Ditto for > prioritised bio dispatch - CFQ supports it but none of the others > do. There's nothing wrong with adding BIO_META (for example) and other hints in _principle_. You should be able to ignore it with no adverse effects. If its not used by a filesystem (and there's nothing else competing to use the same disk), I would hope to see the same performance as other kernels which don't have it. If the elevators are being changed in such a way that old filesystem code which doesn't use new hint bits is running significantly slower, surely that's blatant elevator regression, and that's where the bugs should be reported and fixed? -- Jamie -- 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
