We're moving towards a world in which purging decisions are less rigidly
enforced at a single-hugepage level. In that world, it makes sense to keep
around some hpdatas which are not completely purged, in which case we'll need to
track them.
Really, this isn't a functional change, just a naming change. We start thinking
of pageslabs as being always in the psset. What we used to think of as removal
is now thought of as being in the psset, but in the process of being updated
(and therefore, unavalable for serving new allocations).
This is in preparation of subsequent changes to support deferred purging;
allocations will still be in the psset for the purposes of choosing when to
purge, but not for purposes of allocation/deallocation.
This is really only useful for human consumption. Correspondingly, emit it only
in the human-readable stats, and let everybody else compute from the hugepage
size and nactive.
Previously, we would purge a hugepage only when it's completely empty. With
this change, we can purge even when only partially empty. Although the
heuristic here is still fairly primitive, this infrastructure can scale to
become more advanced.
This is no longer part of the "core" functionality; we only need the stub
implementations as an end-to-end test of hpdata + psset interactions when
metadata is being modified. Treat them accordingly.
Using an edata_t both for hugepages and the allocations within those hugepages
was convenient at first, but has outlived its usefulness. Representing
hugepages explicitly, with their own data structure, will make future
development easier.
This functions more like the serial number strategy of the ecache and
hpa_central_t. Longer-lived slabs are more likely to continue to live for
longer in the future.
This introduces a new sort of edata_t; a pageslab, and a set to manage them.
This is part of a series of a commits to implement a hugepage allocator; the
pageset will be per-arena, and track small page allocations requests within a
larger extent allocated from a centralized hugepage allocator.
