We do special handling of LVM and md in xfs_super.c:xfs_alloc_buftarg(), (and page_buf.c:_pagebuf_page_io()) using only sector-sized buffer heads for pagebufs in the LVM case, and only aligned I/O in the md case. If you had xfs -> md -> lvm -> scsi, then I think this might explain your problem, since XFS thinks it's talking to md, when in fact there is LVM (more restrictive I/O) underneath it. However, you say that you have xfs -> lvm -> md -> scsi, so I am still confused... Just for fun, you could try always setting btp->pbr_flags = PBR_SECTOR_ONLY; in xfs_alloc_buftarg, and see if it makes a difference? -Eric On Fri, 2002-10-25 at 11:54, Luben Tuikov wrote: > As the folks on linux-xfs know, I've recently tried to > get xfs on top of lvm on top of raid5 on top of some > scsi disks to work. > > Here are some recent curiosities which for now seem > to reconcile mount-s in D and BUG() in unlock_page(): > > Here is the basic framework: > > FS --> LVM --> md(raid5) --> scsi disks (1) > > when FS = ext2, the above set up works alright, > when FS = xfs, then as you know either mount > would sleep indefinitely on down(), or BUG() in unlock_page(). > > I've written a tiny SCSI simulator driver for > block devices (non-SCSI; unrelated to all this), > lets call it ``sbs''. > > Strangely when the above set up is like so: > > xfs --> LVM --> sbs --> md(raid5) --> scsi disks (2) > > then everything works all right. > > The only way I can explain this, is that the transformation > that bh's get along the way down and up somehow confuse > xfs in setup (1), (remember ext2 works all right in (1)), > but when sbs is in between LVM and md then things are ok > for xfs. > > This ``solution'', was prompted by other curiosities we found > out here, like when either md or LVM was missing from (1) > with xfs, then things worked ok. > > So, to make everyone happy, we put sbs in the middle of > LVM and md (see (2)), so that from xfs's point of view > it looks like LVM is talking to a scsi block device, and > from md's point of view it looks like it (md) is getting > its bh's from the linux block layer. > > I hope those curiosities help ppl get some/any clue(s) > as to what could be happening and resolve this -- especially > those who know what fs/xfs/pagebuf/*.c is all about... > > Bh's transformation, collecting them back into a page in > xfs from xx_end_io(), etc... where could it be? > > -- > Luben > > P.S. No sensible performance penalties for putting sbs in > the middle. But that's irrelevant. > -- Eric Sandeen XFS for Linux http://oss.sgi.com/projects/xfs sandeen@sgi.com SGI, Inc. 651-683-3102 _______________________________________________ linux-lvm mailing list linux-lvm@sistina.com http://lists.sistina.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
