On Mon, Apr 30 2012 at 2:36pm -0400, Alasdair G Kergon <agk@xxxxxxxxxx> wrote: > On Mon, Apr 30, 2012 at 01:24:00PM -0400, Mike Snitzer wrote: > > On Mon, Apr 30 2012 at 12:10pm -0400, > > Alasdair G Kergon <agk@xxxxxxxxxx> wrote: > > > On Sat, Apr 28, 2012 at 12:44:28AM -0400, Mike Snitzer wrote: > > > > Required to support a target's use of a non power of 2 blocksize. > > > For which targets? > > striped and thin-pool for starters. > > > (merge_bvec supported?) > > Yes. > > But there's overlap between merge_bvec and split_io. > - Why does stripe_merge() have: > > if (!q->merge_bvec_fn) > return max_size; > > when it's already done the division? > > - Couldn't that be changed to avoid split_io causing a split? > (Except, as ever, across a table reload, which prevents us > removing it completely.) > > > I cannot see why we'd need a split_io that is larger than 32 bits -- a > > 32bit split_io can support up to 2TB (2**32 * 512b sectors). Even > > on a LBD (raid) the stripe size (split_io) will not be so large. > > But is that enforced in the raid code or not? No idea, need Jon to weigh in here. I'm hopeful we can impose 32bit within dm-raid and coordinate with Neil on getting the appropriate MD code (chunk_sectors) to reflect the reality that 32 bit is adequate. > > But what I think what you're driving at is: > > (I'm not convinced the proposed patch has been tested on 32-bit+LBD, > attempting to divide by a 64-bit number etc.) Right, it wasn't tested on 32bit. It'll fail to build due to split_io being sector_t. > > is there a benefit/reason to > > maintain the old code for some target that won't ever use non power of 2 > > split_io (e.g. dm-raid at the moment)? I see no point for the duality > > in the code but I'm open to the idea if you have a specific reason in > > mind -- are you concerned about perf on more obscure/older hardware? > > EITHER the 32 bit split_io *must* be enforced (after we've convinced > ourselves 64 bits will never be required); > OR we keep it 64-bit and add some compat code. Yeap, I'm hopeful we can go with the former. Jon, what do you think? -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
