This will eventually completely wrap the eset, and handle concurrency,
allocation, and deallocation. For now, we only pull out the mutex from the
eset.
If there are custom extent hooks, pages_can_purge_lazy is not necessarily the
right guard. We could check ehooks_are_default too, but the case where
purge_lazy is unsupported is rare and getting rarer. Just checking the decay
interval captures most of the benefit.
We have to work to circumvent the safety checks in pre_reentrancy when going
down extent hook pathways. Instead, let's explicitly have checked and unchecked
guards.
When deferred initialization was added, initializing required copying
sizeof(extent_hooks_t) bytes after a pointer chase. Today, it's just a single
pointer loaded from the base_t. In subsequent diffs, we'll get rid of even that.
Explicitly define three setters:
- `prof_tctx_reset()`: set `prof_tctx` to `1U`, if we don't know in
advance whether the allocation is large or not;
- `prof_tctx_reset_sampled()`: set `prof_tctx` to `1U`, if we already
know in advance that the allocation is large;
- `prof_info_set()`: set a real `prof_tctx`, and also set other
profiling info e.g. the allocation time.
Code structure wise, the prof level is kept as a thin wrapper, the
large level only provides low level setter APIs, and the arena level
carries out the main logic.
Fold the tsd_state check onto the event threshold check. The fast threshold is
set to 0 when tsd switch to non-nominal.
The fast_threshold can be reset by remote threads, to refect the non nominal tsd
state change.
Develop new data structure and code logic for holding profiling
related information stored in the extent that may be needed after the
extent is released, which in particular is the case for the
reallocation code path (e.g. in `rallocx()` and `xallocx()`). The
data structure is a generalization of `prof_tctx_t`: we previously
only copy out the `prof_tctx` before the extent is released, but we
may be in need of additional fields. Currently the only additional
field is the allocation time field, but there may be more fields in
the future.
The restructuring also resolved a bug: `prof_realloc()` mistakenly
passed the new `ptr` to `prof_free_sampled_object()`, but passing in
the `old_ptr` would crash because it's already been released. Now
the essential profiling information is collectively copied out early
and safely passed to `prof_free_sampled_object()` after the extent is
released.
