Previously, we would leak the extent and memory associated with a salvageable
portion of an extent that we were trying to split in three, in the case where
the first split attempt succeeded and the second failed.
Looking at the thread counts in our services, jemalloc's background thread
is useful, but mostly idle. Add a config option to tune down the number of threads.
preserve_lru feature adds lots of complication, for little value.
Removing it means merged extents are re-added to the lru list, and may
take longer to madvise away than they otherwise would.
Canaries after removal seem flat for several services (no change).
"always" marks all user mappings as MADV_HUGEPAGE; while "never" marks all
mappings as MADV_NOHUGEPAGE. The default setting "default" does not change any
settings. Note that all the madvise calls are part of the default extent hooks
by design, so that customized extent hooks have complete control over the
mappings including hugepage settings.
We have a buffer overrun that manifests in the case where arena indices higher
than the number of CPUs are accessed before arena indices lower than the number
of CPUs. This fixes the bug and adds a test.
On glibc and Android's bionic, strerror_r returns char* when
_GNU_SOURCE is defined.
Add a configure check for this rather than assume glibc is the
only libc that behaves this way.
We compute the max size required to satisfy an alignment. However this can be
quite pessimistic, especially with frequent reuse (and combined with state-based
fragmentation). This commit adds one more fit step specific to aligned
allocations, searching in all potential fit size classes.
The arena-associated stats are now all prefixed with arena_stats_, and live in
their own file. Likewise, malloc_bin_stats_t -> bin_stats_t, also in its own
file.
When purging, large allocations are usually the ones that cross the npages_limit
threshold, simply because they are "large". This means we often leave the large
extent around for a while, which has the downsides of: 1) high RSS and 2) more
chance of them getting fragmented. Given that they are not likely to be reused
very soon (LRU), let's over purge by 1 extent (which is often large and not
reused frequently).
