• Dan Williams's avatar
    libnvdimm/region: Introduce an 'align' attribute · 2522afb8
    Dan Williams authored
    The align attribute applies an alignment constraint for namespace
    creation in a region. Whereas the 'align' attribute of a namespace
    applied alignment padding via an info block, the 'align' attribute
    applies alignment constraints to the free space allocation.
    The default for 'align' is the maximum known memremap_compat_align()
    across all archs (16MiB from PowerPC at time of writing) multiplied by
    the number of interleave ways if there is blk-aliasing. The minimum is
    PAGE_SIZE and allows for the creation of cross-arch incompatible
    namespaces, just as previous kernels allowed, but the expectation is
    cross-arch and mode-independent compatibility by default.
    The regression risk with this change is limited to cases that were
    dependent on the ability to create unaligned namespaces, *and* for some
    reason are unable to opt-out of aligned namespaces by writing to
    'regionX/align'. If such a scenario arises the default can be flipped
    from opt-out to opt-in of compat-aligned namespace creation, but that is
    a last resort. The kernel will otherwise continue to support existing
    defined misaligned namespaces.
    Unfortunately this change needs to touch several parts of the
    implementation at once:
    - region/available_size: expand busy extents to current align
    - region/max_available_extent: expand busy extents to current align
    - namespace/size: trim free space to current align
    ...to keep the free space accounting conforming to the dynamic align
    Reported-by: default avatarAneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
    Reported-by: default avatarJeff Moyer <jmoyer@redhat.com>
    Reviewed-by: default avatarAneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
    Reviewed-by: default avatarJeff Moyer <jmoyer@redhat.com>
    Link: https://lore.kernel.org/r/158041478371.3889308.14542630147672668068.stgit@dwillia2-desk3.amr.corp.intel.comSigned-off-by: default avatarDan Williams <dan.j.williams@intel.com>
dimm_devs.c 22 KB