tree 2dea429bb8709e746ca83a5a73a13296757a6209
parent d7be9385609328a03c5cfe775473a7dc8e014fd3
author Todd Lipcon <todd@cloudera.com> 1521305014 -0700
committer Todd Lipcon <todd@cloudera.com> 1521305188 -0700

Add a central free list for kMaxPages-sized spans

Previously, the central free list with index '0' was always unused,
since freelist index 'i' tracked spans of length 'i' and there are no
spans of length 0. This meant that there was no freelist for spans of
length 'kMaxPages'. In the default configuration, this corresponds to
1MB, which is a relatively common allocation size in a lot of
applications.

This changes the free list indexing so that index 'i' tracks spans of
length 'i + 1', meaning that free list index 0 is now used and
freelist[kMaxPages - 1] tracks allocations of kMaxPages size (1MB by
default).

This also fixes the stats output to indicate '>128' for the large spans
stats rather than the incorrect '>255' which must have referred to a
historical value of kMaxPages.

No new tests are added since this code is covered by existing tests.