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    SubjectRe: [PATCH 21/26] dax/region: Prevent range mapping allocation on sparse regions
    On Sun, Mar 24, 2024 at 04:18:24PM -0700, Ira Weiny wrote:

    Perhaps lead w some words from prior patch to provide context:

    "DAX regions mapping dynamic capacity partitions introduce a requirement
    for the memory backing the region to come and go as required. This
    results in a DAX region with sparse areas of memory backing."

    Or should this fold into:
    dax/region: Create extent resources on DAX region driver load

    > Sparse regions are not fully populated with memory and this complicates
    > range mapping of dax devices on those regions. There is no use case for
    > range mapping on sparse regions.
    >
    > Avoid the complication by prevent range mapping of dax devices on sparse
    > regions.

    >
    > Signed-off-by: Ira Weiny <ira.weiny@intel.com>
    > ---
    > drivers/dax/bus.c | 2 ++
    > 1 file changed, 2 insertions(+)
    >
    > diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
    > index bab19fc578d0..56dddaceeccb 100644
    > --- a/drivers/dax/bus.c
    > +++ b/drivers/dax/bus.c
    > @@ -1452,6 +1452,8 @@ static umode_t dev_dax_visible(struct kobject *kobj, struct attribute *a, int n)
    > return 0;
    > if (a == &dev_attr_mapping.attr && is_static(dax_region))
    > return 0;
    > + if (a == &dev_attr_mapping.attr && is_sparse(dax_region))
    > + return 0;
    > if ((a == &dev_attr_align.attr ||
    > a == &dev_attr_size.attr) && is_static(dax_region))
    > return 0444;
    >
    > --
    > 2.44.0
    >

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