This pulls out the various abstractions where some stats counter is sometimes an
atomic, sometimes a plain variable, sometimes always protected by a lock,
sometimes protected by reads but not writes, etc. With this change, these cases
are treated consistently, and access patterns tagged.
In the process, we fix a few missed-update bugs (where one caller assumes
"protected-by-a-lock" semantics and another does not).
This is logically at a higher level of the stack; extent should just allocate
things at the page-level; it shouldn't care exactly why the callers wants a
given number of pages.
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.)
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).
With this, we track all of the empty, full, and low water states together. This
simplifies a lot of the tracking logic, since we now don't need the
cache_bin_info_t for state queries (except for some debugging).
I.e. the tcache code just calls a cache-bin function to finish flush (and move
pointers around, etc.). It doesn't directly access the cache-bin's owned memory
any more.
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).
The small and large pathways share most of their logic, even if some of the
individual operations are different. We pull out the common logic into a
force-inlined function, and then specialize twice, once for each value of
"small".
The only time sharing an rtree context saves across extent operations isn't a
no-op is when tsd is unavailable. But this happens only in situations like
thread death or initialization, and we don't care about shaving off every
possible cycle in such scenarios.
Previously, tcache fill/flush (as well as small alloc/dalloc on the arena) may
potentially drop the bin lock for slab_alloc and slab_dalloc. This commit
refactors the logic so that the slab calls happen in the same function / level
as the bin lock / unlock. The main purpose is to be able to use flat combining
without having to keep track of stack state.
In the meantime, this change reduces the locking, especially for slab_dalloc
calls, where nothing happens after the call.
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).
Eventually, we may fully break off the extent module; but not for some time. If
it's going to live on in a non-transitory state, it might as well have the nicer
name.
What we call an arena_ind is really the index associated with some particular
set of ehooks; the arena is just the user-visible portion of that. Making this
explicit, and reframing checks in terms of that, makes the code simpler and
cleaner, and helps us avoid passing the arena itself all throughout extent code.
This lets us put back an arena-specific assert.
Previously, it was really more like extents_alloc (it looks in an ecache for an
extent to reuse as its primary allocation pathway). Make that pathway more
explciitly like extents_alloc, and rename extent_alloc_wrapper_hard accordingly.
This will eventually completely wrap the eset, and handle concurrency,
allocation, and deallocation. For now, we only pull out the mutex from the
eset.
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.
Summary:
Add support for C++17 over-aligned allocation:
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0035r4.html
Supporting all 10 operators means we avoid thunking thru libstdc++-v3/libsupc++ and just call jemalloc directly.
It's also worth noting that there is now an aligned *and sized* operator delete:
```
void operator delete(void* ptr, std::size_t size, std::align_val_t al) noexcept;
```
If JeMalloc did not provide this, the default implementation would ignore the size parameter entirely:
https://github.com/gcc-mirror/gcc/blob/master/libstdc%2B%2B-v3/libsupc%2B%2B/del_opsa.cc#L30-L33
(I must also update ax_cxx_compile_stdcxx.m4 to a newer version with C++17 support.)
Test Plan:
Wrote a simple test that allocates and then deletes an over-aligned type:
```
struct alignas(32) Foo {};
Foo *f;
int main()
{
f = new Foo;
delete f;
}
```
Before this change, both new and delete go thru PLT, and we end up calling regular old free:
```
(gdb) disassemble
Dump of assembler code for function main():
...
0x00000000004029b7 <+55>: call 0x4022d0 <_ZnwmSt11align_val_t@plt>
...
0x00000000004029d5 <+85>: call 0x4022e0 <_ZdlPvmSt11align_val_t@plt>
...
(gdb) s
free (ptr=0x7ffff6408020) at /home/engshare/third-party2/jemalloc/master/src/jemalloc.git-trunk/src/jemalloc.c:2842
2842 if (!free_fastpath(ptr, 0, false)) {
```
After this change, we directly call new/delete and ultimately call sdallocx:
```
(gdb) disassemble
Dump of assembler code for function main():
...
0x0000000000402b77 <+55>: call 0x496ca0 <operator new(unsigned long, std::align_val_t)>
...
0x0000000000402b95 <+85>: call 0x496e60 <operator delete(void*, unsigned long, std::align_val_t)>
...
(gdb) s
116 je_sdallocx_noflags(ptr, size);
```
Makes the prof sample prng use the tsd prng_state. This allows us to properly
initialize the sample interval event, without having to create tdata. As a
result, tdata will be created on demand (when a thread reaches the sample
interval bytes allocated), instead of on the first allocation.
Clang since r369414 (clang-10) can now check -Wimplicit-fallthrough for
C code, and use the GNU C style attribute to denote fallthrough.
Move the test from header only to autoconf. The previous test used
brittle version detection which did not work for newer clang that
supported this feature.
The attribute has to be its own statement, hence the added `;`. It also
can only precede case statements, so the final cases should be
explicitly terminated with break statements.
Fixes commit 3d29d11ac2 ("Clean compilation -Wextra")
Link: 1e0affb6e5
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
`tcache_bin_info` is not accessed on malloc fast path but the
compiler reserves a register for it, as well as an additional
register for `tcache_bin_info[ind].stack_size`. The optimization
gets rid of the need for the two registers.
This change suppresses tdata initialization and prof sample threshold
update in interrupting malloc calls. Interrupting calls have no need
for tdata. Delaying tdata creation aligns better with our lazy tdata
creation principle, and it also helps us gain control back from
interrupting calls more quickly and reduces any risk of delegating
tdata creation to an interrupting call.
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.
Added a new stats row to aggregate the maximum value of mutex counters for each
background threads. Given that the per bg thd mutex is not expected to be
contended, this counter is mainly for sanity check / debugging.
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.
Refactored core profiling codebase into two logical parts:
(a) `prof_data.c`: core internal data structure managing & dumping;
(b) `prof.c`: mutexes & outward-facing APIs.
Some internal functions had to be exposed out, but there are not
that many of them if the modularization is (hopefully) clean enough.
Prof logging is conceptually seperate from core profiling, so
split it out as a module of its own. There are a few internal
functions that had to be exposed but I think it is a fair trade-off.
Augmented the tsd layout graph so that the two recently added fields,
`offset_state` and `bytes_until_sample`, are properly reflected.
As is shown, the cache footprint is 16 bytes larger than before.
Refactored core profiling codebase into two logical parts:
(a) `prof_data.c`: core internal data structure managing & dumping;
(b) `prof.c`: mutexes & outward-facing APIs.
Some internal functions had to be exposed out, but there are not
that many of them if the modularization is (hopefully) clean enough.
`prof.c` is growing too long, so trying to modularize it. There are
a few internal functions that had to be exposed but I think it is a
fair trade-off.
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.
`cbopaque` can now be overriden without overriding `write_cb` in
the first place. (Otherwise there would be no need to have the
`cbopaque` parameter in `malloc_message`.)
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.
Small is added purely for convenience. Large flushes wasn't tracked before and
can be useful in analysis. Large fill simply reports nmalloc, since there is no
batch fill for large currently.
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.
Mainly fixing typos. The only non-trivial change is in the
computation for SC_NPSIZES, though the result wouldn't be any
different when SC_NGROUP = 4 as is always the case at the moment.
Summary: sdallocx is checking a flag that will never be set (at least in the provided C++ destructor implementation). This branch will probably only rarely be mispredicted however it removes two instructions in sdallocx and one at the callsite (to zero out flags).
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.
This fixes a build failure when integrating with FreeBSD's libc. This
regression was introduced by d1e11d48d4
(Move tsd link and in_hook after tcache.).
This feature uses an dedicated arena to handle huge requests, which
significantly improves VM fragmentation. In production workload we tested it
often reduces VM size by >30%.
For low arena count settings, the huge threshold feature may trigger an unwanted
bg thd creation. Given that the huge arena does eager purging by default,
bypass bg thd creation when initializing the huge arena.
When custom extent_hooks or transparent huge pages are in use, the purging
semantics may change, which means we may not get zeroed pages on repopulating.
Fixing the issue by manually memset for such cases.
This makes it possible to have multiple set of bins in an arena, which improves
arena scalability because the bins (especially the small ones) are always the
limiting factor in production workload.
A bin shard is picked on allocation; each extent tracks the bin shard id for
deallocation. The shard size will be determined using runtime options.
If there are 3 or more threads spin-waiting on the same mutex,
there will be excessive exclusive cacheline contention because
pthread_trylock() immediately tries to CAS in a new value, instead
of first checking if the lock is locked.
This diff adds a 'locked' hint flag, and we will only spin wait
without trylock()ing while set. I don't know of any other portable
way to get the same behavior as pthread_mutex_lock().
This is pretty easy to test via ttest, e.g.
./ttest1 500 3 10000 1 100
Throughput is nearly 3x as fast.
This blames to the mutex profiling changes, however, we almost never
have 3 or more threads contending in properly configured production
workloads, but still worth fixing.
For a free fastpath, we want something that will not make additional
calls. Assume most free() calls will hit the L1 cache, and use
a custom rtree function for this.
Additionally, roll the ptr=NULL check in to the rtree cache check.
Nearly all 32-bit powerpc hardware treats lwsync as sync, and some cores
(Freescale e500) trap lwsync as an illegal instruction, which then gets
emulated in the kernel. To avoid unnecessary traps on the e500, use
sync on all 32-bit powerpc. This pessimizes 32-bit software running on
64-bit hardware, but those numbers should be slim.
The diff 'refactor prof accum...' moved the bytes_until_sample
subtraction before the load of tdata. If tdata is null,
tdata_get(true) will overwrite bytes_until_sample, but we
still sample the current allocation. Instead, do the subtraction
and check logic again, to keep the previous behavior.
blame-rev: 0ac524308d
The experimental `smallocx` API is not exposed via header files,
requiring the users to peek at `jemalloc`'s source code to manually
add the external declarations to their own programs.
This should reinforce that `smallocx` is experimental, and that `jemalloc`
does not offer any kind of backwards compatiblity or ABI gurantees for it.
---
Motivation:
This new experimental memory-allocaction API returns a pointer to
the allocation as well as the usable size of the allocated memory
region.
The `s` in `smallocx` stands for `sized`-`mallocx`, attempting to
convey that this API returns the size of the allocated memory region.
It should allow C++ P0901r0 [0] and Rust Alloc::alloc_excess to make
use of it.
The main purpose of these APIs is to improve telemetry. It is more accurate
to register `smallocx(size, flags)` than `smallocx(nallocx(size), flags)`,
for example. The latter will always line up perfectly with the existing
size classes, causing a loss of telemetry information about the internal
fragmentation induced by potentially poor size-classes choices.
Instrumenting `nallocx` does not help much since user code can cache its
result and use it repeatedly.
---
Implementation:
The implementation adds a new `usize` option to `static_opts_s` and an `usize`
variable to `dynamic_opts_s`. These are then used to cache the result of
`sz_index2size` and similar functions in the code paths in which they are
unconditionally invoked. In the code-paths in which these functions are not
unconditionally invoked, `smallocx` calls, as opposed to `mallocx`, these
functions explicitly.
---
[0]: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0901r0.html
generation of sub bytes_until_sample, usize; je; for x86 arch.
Subtraction is unconditional, and only flags are checked for the jump,
no extra compare is necessary. This also reduces register pressure.
