From: Tyler Hicks <tyhicks@linux.microsoft.com>
To: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>,
linux-nvdimm@lists.01.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] libnvdimm/region: Allow setting align attribute on regions without mappings
Date: Tue, 30 Mar 2021 10:43:15 -0500 [thread overview]
Message-ID: <20210330154315.GD4749@sequoia> (raw)
In-Reply-To: <87h7ks7vm5.fsf@linux.ibm.com>
On 2021-03-30 16:32:10, Aneesh Kumar K.V wrote:
> Tyler Hicks <tyhicks@linux.microsoft.com> writes:
>
> > The alignment constraint for namespace creation in a region was
> > increased, from 2M to 16M, for non-PowerPC architectures in v5.7 with
> > commit 2522afb86a8c ("libnvdimm/region: Introduce an 'align'
> > attribute"). The thought behind the change was that region alignment
> > should be uniform across all architectures and, since PowerPC had the
> > largest alignment constraint of 16M, all architectures should conform to
> > that alignment.
> >
> > The change regressed namespace creation in pre-defined regions that
> > relied on 2M alignment but a workaround was provided in the form of a
> > sysfs attribute, named 'align', that could be adjusted to a non-default
> > alignment value.
> >
> > However, the sysfs attribute's store function returned an error (-ENXIO)
> > when userspace attempted to change the alignment of a region that had no
> > mappings. This affected 2M aligned regions of volatile memory that were
> > defined in a device tree using "pmem-region" and created by the
> > of_pmem_region_driver, since those regions do not contain mappings
> > (ndr_mappings is 0).
> >
> > Allow userspace to set the align attribute on pre-existing regions that
> > do not have mappings so that namespaces can still be within those
> > regions, despite not being aligned to 16M.
> >
> > Fixes: 2522afb86a8c ("libnvdimm/region: Introduce an 'align' attribute")
> > Signed-off-by: Tyler Hicks <tyhicks@linux.microsoft.com>
> > ---
> > drivers/nvdimm/region_devs.c | 33 ++++++++++++++++++---------------
> > 1 file changed, 18 insertions(+), 15 deletions(-)
> >
> > diff --git a/drivers/nvdimm/region_devs.c b/drivers/nvdimm/region_devs.c
> > index ef23119db574..09cff8aa6b40 100644
> > --- a/drivers/nvdimm/region_devs.c
> > +++ b/drivers/nvdimm/region_devs.c
> > @@ -545,29 +545,32 @@ static ssize_t align_store(struct device *dev,
> > struct device_attribute *attr, const char *buf, size_t len)
> > {
> > struct nd_region *nd_region = to_nd_region(dev);
> > - unsigned long val, dpa;
> > - u32 remainder;
> > + unsigned long val;
> > int rc;
> >
> > rc = kstrtoul(buf, 0, &val);
> > if (rc)
> > return rc;
> >
> > - if (!nd_region->ndr_mappings)
> > - return -ENXIO;
> > -
> > - /*
> > - * Ensure space-align is evenly divisible by the region
> > - * interleave-width because the kernel typically has no facility
> > - * to determine which DIMM(s), dimm-physical-addresses, would
> > - * contribute to the tail capacity in system-physical-address
> > - * space for the namespace.
> > - */
> > - dpa = div_u64_rem(val, nd_region->ndr_mappings, &remainder);
> > - if (!is_power_of_2(dpa) || dpa < PAGE_SIZE
> > - || val > region_size(nd_region) || remainder)
> > + if (val > region_size(nd_region))
> > return -EINVAL;
> >
> > + if (nd_region->ndr_mappings) {
> > + unsigned long dpa;
> > + u32 remainder;
> > +
> > + /*
> > + * Ensure space-align is evenly divisible by the region
> > + * interleave-width because the kernel typically has no facility
> > + * to determine which DIMM(s), dimm-physical-addresses, would
> > + * contribute to the tail capacity in system-physical-address
> > + * space for the namespace.
> > + */
> > + dpa = div_u64_rem(val, nd_region->ndr_mappings, &remainder);
> > + if (!is_power_of_2(dpa) || dpa < PAGE_SIZE || remainder)
> > + return -EINVAL;
> > + }
>
> We still want
>
> else {
>
> if (!is_power_of_2(val) || val < PAGE_SIZE)
> return -EINVAL?
Yes, very good point. I'll send out a v2 that ensures val is a power of
2 and at least page size.
Tyler
>
> }
> > +
> > /*
> > * Given that space allocation consults this value multiple
> > * times ensure it does not change for the duration of the
> > --
> > 2.25.1
> > _______________________________________________
> > Linux-nvdimm mailing list -- linux-nvdimm@lists.01.org
> > To unsubscribe send an email to linux-nvdimm-leave@lists.01.org
>
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prev parent reply other threads:[~2021-03-30 15:43 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-26 15:26 [PATCH] libnvdimm/region: Allow setting align attribute on regions without mappings Tyler Hicks
2021-03-26 22:03 ` Pavel Tatashin
2021-03-30 11:02 ` Aneesh Kumar K.V
2021-03-30 15:43 ` Tyler Hicks [this message]
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