RE: [External] Re: [PATCH] libnvdimm, region_devs: stop NDD_ALIASING bit test if one test pass

[Ocean HY1 He]

> -----Original Message-----
> From: Verma, Vishal L <vishal.l.verma@xxxxxxxxx>
> Sent: Friday, August 31, 2018 5:51 AM
> To: Williams, Dan J <dan.j.williams@xxxxxxxxx>; ross.zwisler@xxxxxxxxxxxxxxx;
> oceanhehy@xxxxxxxxx; Jiang, Dave <dave.jiang@xxxxxxxxx>
> Cc: linux-kernel@xxxxxxxxxxxxxxx; linux-nvdimm@xxxxxxxxxxxx; Ocean HY1 He
> <hehy1@xxxxxxxxxx>
> Subject: [External] Re: [PATCH] libnvdimm, region_devs: stop NDD_ALIASING
> bit test if one test pass
> 
> 
> On Sun, 2018-08-19 at 00:01 -0400, Ocean He wrote:
> > From: Ocean He <hehy1@xxxxxxxxxx>
> >
> > There is no need to finish entire loop to execute NDD_ALIASING bit
> > test
> > against every nvdimm->flags. In practice, all the nd_mapping->nvdimm
> > have the same flags.
> >
> > Because the check of alias is "if (alias)" but not
> > "if (alias == nd_region->ndr_mappings)", there is no function change
> > while
> > just save a few cycles.
> >
> > Signed-off-by: Ocean He <hehy1@xxxxxxxxxx>
> > ---
> > A test to check if all the nd_mapping->nvdimm have the same flags,
> > using
> > Lenovo ThinkSystem SR630 and 4.18-rc6.
> >
> > # ipmctl show -dimm
> >
> > DimmID  Capacity        HealthState     ActionRequired  LockState
> >    FWVersion
> > 0x0021  125.7
> > GiB       Healthy         0               Disabled        01.00.00.48
> > 88
> > 0x0121  125.7
> > GiB       Healthy         0               Disabled        01.00.00.48
> > 88
> > 0x1021  125.7
> > GiB       Healthy         0               Disabled        01.00.00.48
> > 88
> > 0x1121  125.7
> > GiB       Healthy         0               Disabled        01.00.00.48
> > 88
> >
> > # ipmctl create -f -goal -socket 0x0 PersistentMemoryType=AppDirect
> >
> > # ipmctl create -f -goal -socket 0x1 PersistentMemoryType=AppDirect
> >
> > # reboot, to make goal configuration take effect.
> >
> > # ndctl create-namespace -r region0 -s 100m -t pmem -m fsdax
> >
> > # ndctl create-namespace -r region1 -s 100m -t pmem -m fsdax
> >
> > # reboot and find all the nd_mapping->nvdimm have the same flags.
> >
> >  drivers/nvdimm/region_devs.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/nvdimm/region_devs.c
> > b/drivers/nvdimm/region_devs.c
> > index ec3543b..fc3bc1c 100644
> > --- a/drivers/nvdimm/region_devs.c
> > +++ b/drivers/nvdimm/region_devs.c
> > @@ -234,8 +234,10 @@ int nd_region_to_nstype(struct nd_region
> > *nd_region)
> >  			struct nd_mapping *nd_mapping = &nd_region-
> > >mapping[i];
> >  			struct nvdimm *nvdimm = nd_mapping->nvdimm;
> >
> > -			if (test_bit(NDD_ALIASING, &nvdimm->flags))
> > +			if (test_bit(NDD_ALIASING, &nvdimm->flags))
> > {
> >  				alias++;
> > +				break;
> 
> I think we can go a step further, and instead of the 'break' followed
> by a check for the 'alias' variable, in the loop, just return
> ND_DEVICE_NAMESPACE_PMEM if the NDD_ALIASING bit is found for any
> mapping. Outside the loop, simply return ND_DEVICE_NAMESPACE_IO. That
> makes it much cleaner and now we can get rid of 'alias' entirely.
> 
Hi Vishal,

Thanks for comments and I would send version 2 patch later.

Ocean.
> > +			}
> >  		}
> >  		if (alias)
> >  			return ND_DEVICE_NAMESPACE_PMEM;