Dan Williams <dan.j.willi...@intel.com> writes: > 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 > setting. > > Reported-by: Aneesh Kumar K.V <aneesh.ku...@linux.ibm.com> > Reported-by: Jeff Moyer <jmo...@redhat.com> > Signed-off-by: Dan Williams <dan.j.willi...@intel.com> > Reviewed-by: Aneesh Kumar K.V <aneesh.ku...@linux.ibm.com> > Link: > https://lore.kernel.org/r/158041478371.3889308.14542630147672668068.st...@dwillia2-desk3.amr.corp.intel.com > Signed-off-by: Dan Williams <dan.j.willi...@intel.com>
This looks good to me. Reviewed-by: Jeff Moyer <jmo...@redhat.com>
