Per the doc, usage must be kept maximally merged. Beyond that, it is simply a
good idea to keep fragmentation in usage to a minimum.
The glibc malloc allocator allocates one page at a time, potentially causing
lots of fragmentation. However, those pages are likely to have the same number
of references, often making it possible to merge ranges.
PiperOrigin-RevId: 204960339
Change-Id: I03a050cf771c29a4f05b36eaf75b1a09c9465e14
If usageSet is heavily fragmented, findUnallocatedRange and findReclaimable
can spend excessive cycles linearly scanning the set for unallocated/free
pages.
Improve common cases by beginning the scan only at the first page that could
possibly contain an unallocated/free page. This metadata only guarantees that
there is no lower unallocated/free page, but a scan may still be required
(especially for multi-page allocations).
That said, this heuristic can still provide significant performance
improvements for certain applications.
PiperOrigin-RevId: 204841833
Change-Id: Ic41ad33bf9537ecd673a6f5852ab353bf63ea1e6
Ian Gudger
Fabricio Voznika
Zhaozhong Ni
Michael Pratt
Jamie Liu
Googler