The goal of `qr_meld()` is to change the following four fields
`(a->prev, a->prev->next, b->prev, b->prev->next)` from the values
`(a->prev, a, b->prev, b)` to `(b->prev, b, a->prev, a)`.
This commit changes
```
a->prev->next = b;
b->prev->next = a;
temp = a->prev;
a->prev = b->prev;
b->prev = temp;
```
to
```
temp = a->prev;
a->prev = b->prev;
b->prev = temp;
a->prev->next = a;
b->prev->next = b;
```
The benefit is that we can use `b->prev->next` for `temp`, and so
there's no need to pass in `a_type`.
The restriction is that `b` cannot be a `qr_next()` macro, so users
of `qr_meld()` must pay attention. (Before this change, neither `a`
nor `b` could be a `qr_next()` macro.)
Previously, large allocations in tcaches would have their sizes reduced during
stats estimation. Added a test, which fails before this change but passes now.
This fixes a bug introduced in 5934846612, which
was itself fixing a bug introduced in 9c0549007d.
This lets us put more allocations on an "almost as fast" path after a flush.
This results in around a 4% reduction in malloc cycles in prod workloads
(corresponding to about a 0.1% reduction in overall cycles).
Previously, we took an array of cache_bin_info_ts and an index, and dereferenced
ourselves. But infos for other cache_bins aren't relevant to any particular
cache bin, so that should be the caller's job.
This is debug only and we keep it off the fast path. Moving it here simplifies
the internal logic.
This never tries to junk on regions that were shrunk via xallocx. I think this
is fine for two reasons:
- The shrunk-with-xallocx case is rare.
- We don't always do that anyway before this diff (it depends on the opt
settings and extent hooks in effect).
Make the event module to accept two event types, and pass around the event
context. Use bytes-based events to trigger tcache GC on deallocation, and get
rid of the tcache ticker.
Add options stats_interval and stats_interval_opts to allow interval based stats
printing. This provides an easy way to collect stats without code changes,
because opt.stats_print may not work (some binaries never exit).
This will eventually completely wrap the eset, and handle concurrency,
allocation, and deallocation. For now, we only pull out the mutex from the
eset.
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.
Specifically, the extent_arena_[g|s]et functions and the address randomization.
These are the only things that tie the extent struct itself to the arena code.
The -1 value of low_water indicates if the cache has been depleted and
refilled. Track the status explicitly in the tcache struct.
This allows the fast path to check if (cur_ptr > low_water), instead of >=,
which avoids reaching slow path when the last item is allocated.
With the cache bin metadata switched to pointers, ncached_max is usually
accessed and timed by sizeof(ptr). Store the results in tcache_bin_info for
direct access, and add a helper function for the ncached_max value.
Implement the pointer-based metadata for tcache bins --
- 3 pointers are maintained to represent each bin;
- 2 of the pointers are compressed on 64-bit;
- is_full / is_empty done through pointer comparison;
Comparing to the previous counter based design --
- fast-path speed up ~15% in benchmarks
- direct pointer comparison and de-reference
- no need to access tcache_bin_info in common case
JSON format is largely meant for machine-machine communication, so
adding the option to the emitter. According to local testing, the
savings in terms of bytes outputted is around 50% for stats printing
and around 25% for prof log printing.
The VirtualAlloc and VirtualFree APIs are different because MEM_DECOMMIT cannot
be used across multiple VirtualAlloc regions. To properly support decommit,
only allow merge / split within the same region -- this is done by tracking the
"is_head" state of extents and not merging cross-region.
Add a new state is_head (only relevant for retain && !maps_coalesce), which is
true for the first extent in each VirtualAlloc region. Determine if two extents
can be merged based on the head state, and use serial numbers for sanity checks.
If the confirm_conf option is set, when the program starts, each of
the four malloc_conf strings will be printed, and each option will
be printed when being set.
When config_stats is enabled track the size of bin->slabs_nonfull in
the new nonfull_slabs counter in bin_stats_t. This metric should be
useful for establishing an upper ceiling on the savings possible by
meshing.
The analytics tool is put under experimental.utilization namespace in
mallctl. Input is one pointer or an array of pointers and the output
is a list of memory utilization statistics.
