Hi Andreas, only a short question: > I like the idea of keeping the high bits of the buddy bitmap in the group > descriptor, instead of just the largest free order. It takes the same > amount of space, but provides more information. More informations for what? The allocator or better the good_group function needs bb_largest_free_order and in some cases fragment count. Do you want to use the bitmap for a not 100% correct fragment count calculation? Or is there another use for it? Best regards, Frank > > > On Sun, 19 May 2013 21:36:02 +0200 (CEST) Frank C Moeller wrote: > >> From my point (end user) I would prefer a builtin solution. I'm also a > >> programmer and I can therefore understand why you don't want to change > >> anything. > > > > It's not that I don't want to change anything, it's that I'm very > > hesitant to add new mount options or new code paths that now need more > > testing unless there's no other way of addressing a particular use > > case. Another consideration is how to do it in such a way that it > > doesn't degrade other users' performance. > > > > Issuing readahead requests for the bitmap blocks might be good > > compromise; since they are readahead requests, as low priority > > requests they won't interfere with anything else going on, and in > > practice, unless you are starting your video recording **immediately** > > after the reboot, it should address your concern. > > Right. Some of our users do something similar in userspace to avoid > slowdown on first write, which doesn't _usually_ happen immediately > after mount, but this isn't always helpful. > > > (Also note that for > > most people willing to hack a DVR, adding a line to /etc/rc.local is > > usually considered easier than building a new kernel from sources and > > then after making file system format changes, requiring a reformat of > > their data disk!) > > I think storing the buddy bitmap top bits in the GDT could be a COMPAT > feature. It is just a hint that could be ignored or incorrect, since > the actual bitmap would be authoritative. > > Cheers, Andreas > > > So it's not that I'm against solutions that involve kernel changes or > > file system format changes. It's just that I want to make sure we > > explore the entire solution space, since there are costs in terms of > > testing costs, the need to do a backup-reformat-restore pass, etc, > > etc., to some of the solutions that have been suggested so far. > > > > Regards, > > > > - Ted > -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
