On Thu, Jun 02, 2011 at 03:55:16PM -0400, Mikulas Patocka wrote: > > iv) you haven't explained how the sys admin works out the correct > > throttle value. > > There is no "correct" value. The "correct" value depends on how important > is copying itself v.s. other i/o. So who is going to set this? Do you really have no advice for them beyond 'there is no correct value'? > In theory (if disk scheduler were perfect), we wouldn't need any > throttling. The disk scheduler should recognize that the kcopyd process is > sending way more requests than any other process and should lower the > i/o priority of kcopyd process. > > In practice, the disk scheduler doesn't do it well, so kcopyd hurts the > users. If you want an automated fix, fix the disk scheduler. But don't put > disk scheduler logic into device mapper --- it dosn't belong there. I totally agree with these two paragraphs. Any throttling you add to kcopyd is always going to be a hack. - Joe -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
