Messages in this thread | | | Date | Thu, 10 Jan 2002 12:09:26 +0100 | From | Andrea Arcangeli <> | Subject | Re: [PATCH] PAGE_SIZE IO for RAW (RAW VARY) |
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On Thu, Jan 10, 2002 at 11:51:51AM +0100, Jens Axboe wrote: > On Thu, Jan 10 2002, Andrea Arcangeli wrote: > > On Thu, Jan 10, 2002 at 11:22:25AM +0100, Jens Axboe wrote: > > > On Thu, Jan 10 2002, Andrea Arcangeli wrote: > > > > On Wed, Jan 09, 2002 at 11:28:39AM -0800, Badari Pulavarty wrote: > > > > > Ben, > > > > > > > > > > By any chance do you have a list of drivers that assume this ? > > > > > What does it take to fix them ? > > > > > > > > > > I think Jens BIO changes for 2.5 will fix this problem. But 2.4 > > > > > needs a solution in this area too. This patch showed significant > > > > > improvement for database workloads. > > > > > > > > I didn't checked the implementation but as far as the blkdev is > > > > concerned the b_size changes without notification as soon as you > > > > 'mkfs -b somethingelse' and then mount the fs. So it cannot break > > > > as far I can tell. The only important thing is that b_size stays > > > > between 512 and 4k. > > > > > > The concern is/was differently sized buffer_heads in the same > > > request, ie b_size changing as you iterate through the chunks of one > > > request. > > > > ok, I don't expect problems there. It can happen for example if you > > create a snapshot with 4k and then you switch back the original volume > > to 1k. the physical volume will get mixed b_size colaesced into the > > same request. > > Well I don't expect problems either, however Jeff Merkey did report them > but see my previous mail on that (validity of that report is > questionable). > > I still wouldn't feel to good doing this, and just because snapshotting > opens the possibility for this to happen doesn't mean it a) ever > triggered in real life, and b) works on all devices.
fair enough. one way to do it certainly safely is to add a bitflag to the struct blkkdev.
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