On Fri, 2008-08-08 at 16:20 +0900, Ryo Tsuruta wrote: > > > - Implement a block layer resource controller. dm-ioband is a working > > > solution and feature rich but its dependency on the dm infrastructure is > > > likely to find opposition (the dm layer does not handle barriers > > > properly and the maximum size of I/O requests can be limited in some > > > cases). In such a case, we could either try to build a standalone > > > resource controller based on dm-ioband (which would probably hook into > > > generic_make_request) or try to come up with something new. > > > > I doubt about the maximum size of I/O requests problem. You can't avoid > > this problem as far as you use device mapper modules with such a bad > > manner, even if the controller is implemented as a stand-alone controller. > > There is no limitation if you only use dm-ioband without any other device > > mapper modules. > > The following is a part of source code where the limitation comes from. > > dm-table.c: dm_set_device_limits() > /* > * Check if merge fn is supported. > * If not we'll force DM to use PAGE_SIZE or > * smaller I/O, just to be safe. > */ > > if (q->merge_bvec_fn && !ti->type->merge) > rs->max_sectors = > min_not_zero(rs->max_sectors, > (unsigned int) (PAGE_SIZE >> 9)); > > As far as I can find, In 2.6.27-rc1-mm1, Only some software RAID > drivers and pktcdvd driver define merge_bvec_fn(). Yup, exactly. The implication of this is that we may see a drop in performance in some RAID configurations. -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
