New features:

Add EXTENT_ALLOC_FLAG_PINNED so custom extent-allocation hooks can
mark non-reclaimable mappings, such as HugeTLB pages, for preferential
reuse outside the decay and purge pipeline. Add the mallctl interfaces
stats.pinned, stats.arenas.<i>.pinned,
stats.arenas.<i>.extents.<j>.npinned,
stats.arenas.<i>.extents.<j>.pinned_bytes, and
stats.arenas.<i>.mutexes.extents_pinned.{counter} to report
pinned-memory usage and mutex statistics. (@binliu19: be2de8c)
Allow resuming per-CPU arena selection via thread.arena.
(@Algunenano: 68c35f6)
Better align the contents of human-readable and JSON malloc statistics.
(@spredolac: 68fe1be, 30b1a41, 04aad97)
Replace the runtime experimental_infallible_new option with the
compile-time --enable-cxx-infallible-new option, enabling
compiler-level optimizations and optimization in move constructors,
and fix the new(std::nothrow) contract (@spredolac: 160ab9d, fe33667)

Incompatible changes:

Adapt tcache fill and retention targets per bin to demand observed
between GC events, replacing the fixed refill/flush policy. Remove
seven legacy non-experimental controls: lg_tcache_nslots_mul,
tcache_nslots_small_min, tcache_nslots_small_max,
tcache_nslots_large, tcache_gc_delay_bytes,
lg_tcache_flush_small_div, and lg_tcache_flush_large_div.
Corresponding malloc_conf settings are silently ignored, matching
opt.* mallctls return ENOENT, and tcache_ncached_max remains
supported. (@spredolac: d13fe91)

Bug fixes:

Preserve errno across free, free_sized, and free_aligned_sized,
and across process_madvise-based page purging. (@spredolac: 3a77966,
86f0582)
Fix numeric overflow checks in size classes. (@spredolac: 6b24522)
Accept NULL in free_sized() and free_aligned_sized() (C23
correctness). (@bigbruno: 7ce8b91)
Fix TSD lifecycle edge cases by 1) initializing thread-cache bins before
marking the cache enabled, preventing reentrant bootstrap allocations
from using uninitialized state, and 2) avoiding TSD recreation for late
deallocations after thread teardown on generic-TSD platforms.
(@fzakaria: 54f22c8, @spredolac: fb5499a)
Use O_CLOEXEC when opening the THP sysfs file in init_thp_state.
(@ibookstein: d070554)
Fix duplicate opt.stats_print and opt.stats_print_opts fields in
malloc_stats_print output. (@spredolac: dfe3a2e)
Fix a potential deadlock during arena_reset. (@guangli-dai: 6957341)
Fix a prof-sampling / guard-page interaction bug in the SAN. (@gctony:
e36a0fa)

Optimizations and refactors:

Modularize jemalloc's front end by extracting arena management,
initialization, fork orchestration, and allocation dispatch from
jemalloc.c; untangle tcache/arena ownership; and consolidate the
internal header graph to eliminate circular dependencies. (@spredolac:
ba1e2fe, 8874597, 9d75722, de9ad14, ...)
Simplify ctl dispatch by refactoring arena helpers, internalizing an
implementation-only control, replacing control-flow macros with typed
helpers, and organizing ctl.c by subsystem. (@spredolac: 9e14346,
901365d, 4e903a0, 5bc8d6e)
Cap the base-block growth heuristic to avoid virtual-memory exhaustion
under rare racy conditions. (@guangli-dai: 2f4db8c)
Move background-thread lifecycle and state operations into the
background-thread module, clarifying ownership independently of PAC/HPA
callers. (@guangli-dai: f1f0792)
Simplify the page-allocation boundary by replacing PAI vtable dispatch
with direct PAC/HPA calls, removing the obsolete pai_t/pai.h
abstraction, and moving deferred-work and decay orchestration out of the
arena. (@guangli-dai: 1dfa6f7, 8edd101, d410f43)
Refactor statistics collection and rendering into separate
gather/emission stages and descriptor-driven tables. (@spredolac:
184f304, 80c8fcb)
Introduce an OS abstraction layer and move platform-dependent
file/process I/O, time, synchronization, CPU, virtual-memory, atfork,
error-handling, profiling, thread-yield, and configuration-access
operations out of allocator core code. (@guangli-dai: c4158ac,
c8e2e01, ...)

Portability improvements:

Replace the std::__throw_bad_alloc call with standard C++ (#2900).
(@lexprfuncall: 1a15fe3)
Make arena_s use a flexible array member (bin_t all_bins[]) for C99
or newer. (@grueninger: 300b58b)
Fix rdtscp detection with --with-lg-vaddr. (@xinydev: e8a0d2b)
Fix malloc_getcpu on macOS to read the current CPU number correctly.
(@Algunenano: 5aabbc8)
Use CLOCK_MONOTONIC for background-thread sleep to prevent
clock-rollback stalls, and detect monotonic-condvar support at configure
time. (@antonio2368: ebacec3, 8361239)
Fix compilation warnings on macOS. (@gctony: abb0a8a)
Fix thread-exit TSD cleanup on MinGW builds. (@gctony: 1e92317)
Fix GCC 16 build warnings by removing -Wpedantic violations in macro
and function syntax and explicitly NUL-terminating profiling thread-name
copies to resolve -Wstringop-truncation. (@grueninger: 5acdcee,
c22d929, @jasonangelov: 6a245e0)
Parse PID-namespace symlinks without glibc-dependent strtok/atol,
and return identifiers as uint64_t. (@guangli-dai: 278d90a)
     
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