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    SubjectRe: [PATCH v3 14/14] libnvdimm, pmem: disable dax flushing when pmem is fronting a volatile region
    On Fri, Jun 9, 2017 at 1:25 PM, Dan Williams <dan.j.williams@intel.com> wrote:
    > The pmem driver attaches to both persistent and volatile memory ranges
    > advertised by the ACPI NFIT. When the region is volatile it is redundant
    > to spend cycles flushing caches at fsync(). Check if the hosting region
    > is volatile and do not set QUEUE_FLAG_WC if it is.
    >
    > Cc: Jan Kara <jack@suse.cz>
    > Cc: Jeff Moyer <jmoyer@redhat.com>
    > Cc: Christoph Hellwig <hch@lst.de>
    > Cc: Matthew Wilcox <mawilcox@microsoft.com>
    > Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
    > Signed-off-by: Dan Williams <dan.j.williams@intel.com>
    > ---
    > drivers/nvdimm/pmem.c | 13 ++++++++-----
    > drivers/nvdimm/region_devs.c | 6 ++++++
    > include/linux/libnvdimm.h | 1 +
    > 3 files changed, 15 insertions(+), 5 deletions(-)
    >
    > diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
    > index 06f6c27ec1e9..5cac9fb39db8 100644
    > --- a/drivers/nvdimm/pmem.c
    > +++ b/drivers/nvdimm/pmem.c
    > @@ -279,10 +279,10 @@ static int pmem_attach_disk(struct device *dev,
    > struct nd_namespace_io *nsio = to_nd_namespace_io(&ndns->dev);
    > struct nd_region *nd_region = to_nd_region(dev->parent);
    > struct vmem_altmap __altmap, *altmap = NULL;
    > + int nid = dev_to_node(dev), fua, wbc;
    > struct resource *res = &nsio->res;
    > struct nd_pfn *nd_pfn = NULL;
    > struct dax_device *dax_dev;
    > - int nid = dev_to_node(dev);
    > struct nd_pfn_sb *pfn_sb;
    > struct pmem_device *pmem;
    > struct resource pfn_res;
    > @@ -308,9 +308,12 @@ static int pmem_attach_disk(struct device *dev,
    > dev_set_drvdata(dev, pmem);
    > pmem->phys_addr = res->start;
    > pmem->size = resource_size(res);
    > - if (!IS_ENABLED(CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE)
    > - || nvdimm_has_flush(nd_region) < 0)
    > - dev_warn(dev, "unable to guarantee persistence of writes\n");
    > + fua = nvdimm_has_flush(nd_region);
    > + if (!IS_ENABLED(CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE) || fua < 0)
    > + dev_warn(dev, "unable to guarantee persistence of writes\n"); {

    I sent this patch with local uncommitted changes. Will send a v2
    shortly, and also update stg mail to abort if the tree is dirty.

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