path: root/yjit/src/stats.rs

//! Everything related to the collection of runtime stats in YJIT
//! See the stats feature and the --yjit-stats command-line option

#![allow(dead_code)] // Counters are only used with the stats features

use crate::codegen::CodegenGlobals;
use crate::core::Context;
use crate::core::for_each_iseq_payload;
use crate::cruby::*;
use crate::options::*;
use crate::yjit::yjit_enabled_p;

// stats_alloc is a middleware to instrument global allocations in Rust.
#[cfg(feature="stats")]
#[global_allocator]
static GLOBAL_ALLOCATOR: &stats_alloc::StatsAlloc<std::alloc::System> = &stats_alloc::INSTRUMENTED_SYSTEM;

// YJIT exit counts for each instruction type
const VM_INSTRUCTION_SIZE_USIZE:usize = VM_INSTRUCTION_SIZE as usize;
static mut EXIT_OP_COUNT: [u64; VM_INSTRUCTION_SIZE_USIZE] = [0; VM_INSTRUCTION_SIZE_USIZE];

/// Global state needed for collecting backtraces of exits
pub struct YjitExitLocations {
    /// Vec to hold raw_samples which represent the control frames
    /// of method entries.
    raw_samples: Vec<VALUE>,
    /// Vec to hold line_samples which represent line numbers of
    /// the iseq caller.
    line_samples: Vec<i32>,
    /// Number of samples skipped when sampling
    skipped_samples: usize
}

/// Private singleton instance of yjit exit locations
static mut YJIT_EXIT_LOCATIONS: Option<YjitExitLocations> = None;

impl YjitExitLocations {
    /// Initialize the yjit exit locations
    pub fn init() {
        // Return if the stats feature is disabled
        if !cfg!(feature = "stats") {
            return;
        }

        // Return if --yjit-trace-exits isn't enabled
        if !get_option!(gen_trace_exits) {
            return;
        }

        let yjit_exit_locations = YjitExitLocations {
            raw_samples: Vec::new(),
            line_samples: Vec::new(),
            skipped_samples: 0
        };

        // Initialize the yjit exit locations instance
        unsafe {
            YJIT_EXIT_LOCATIONS = Some(yjit_exit_locations);
        }
    }

    /// Get a mutable reference to the yjit exit locations globals instance
    pub fn get_instance() -> &'static mut YjitExitLocations {
        unsafe { YJIT_EXIT_LOCATIONS.as_mut().unwrap() }
    }

    /// Get a mutable reference to the yjit raw samples Vec
    pub fn get_raw_samples() -> &'static mut Vec<VALUE> {
        &mut YjitExitLocations::get_instance().raw_samples
    }

    /// Get a mutable reference to yjit the line samples Vec.
    pub fn get_line_samples() -> &'static mut Vec<i32> {
        &mut YjitExitLocations::get_instance().line_samples
    }

    /// Get the number of samples skipped
    pub fn get_skipped_samples() -> &'static mut usize {
        &mut YjitExitLocations::get_instance().skipped_samples
    }

    /// Mark the data stored in YjitExitLocations::get_raw_samples that needs to be used by
    /// rb_yjit_add_frame. YjitExitLocations::get_raw_samples are an array of
    /// VALUE pointers, exit instruction, and number of times we've seen this stack row
    /// as collected by rb_yjit_record_exit_stack.
    ///
    /// These need to have rb_gc_mark called so they can be used by rb_yjit_add_frame.
    pub fn gc_mark_raw_samples() {
        // Return if YJIT is not enabled
        if !yjit_enabled_p() {
            return;
        }

        // Return if the stats feature is disabled
        if !cfg!(feature = "stats") {
            return;
        }

        // Return if --yjit-trace-exits isn't enabled
        if !get_option!(gen_trace_exits) {
            return;
        }

        let mut idx: size_t = 0;
        let yjit_raw_samples = YjitExitLocations::get_raw_samples();

        while idx < yjit_raw_samples.len() as size_t {
            let num = yjit_raw_samples[idx as usize];
            let mut i = 0;
            idx += 1;

            // Mark the yjit_raw_samples at the given index. These represent
            // the data that needs to be GC'd which are the current frames.
            while i < i32::from(num) {
                unsafe { rb_gc_mark(yjit_raw_samples[idx as usize]); }
                i += 1;
                idx += 1;
            }

            // Increase index for exit instruction.
            idx += 1;
            // Increase index for bookkeeping value (number of times we've seen this
            // row in a stack).
            idx += 1;
        }
    }
}

// Macro to declare the stat counters
macro_rules! make_counters {
    ($($counter_name:ident,)+) => {
        /// Struct containing the counter values
        #[derive(Default, Debug)]
        pub struct Counters { $(pub $counter_name: u64),+ }

        /// Enum to represent a counter
        #[allow(non_camel_case_types)]
        #[derive(Clone, Copy, PartialEq, Eq, Debug)]
        pub enum Counter { $($counter_name),+ }

        impl Counter {
            /// Get a counter name string
            pub fn get_name(&self) -> String {
                match self {
                    $( Counter::$counter_name => stringify!($counter_name).to_string() ),+
                }
            }
        }

        /// Global counters instance, initialized to zero
        pub static mut COUNTERS: Counters = Counters { $($counter_name: 0),+ };

        /// Counter names constant
        const COUNTER_NAMES: &'static [&'static str] = &[ $(stringify!($counter_name)),+ ];

        /// Map a counter name string to a counter pointer
        pub fn get_counter_ptr(name: &str) -> *mut u64 {
            match name {
                $( stringify!($counter_name) => { ptr_to_counter!($counter_name) } ),+
                _ => panic!()
            }
        }
    }
}

/// Macro to increase a counter by name and count
macro_rules! incr_counter_by {
    // Unsafe is ok here because options are initialized
    // once before any Ruby code executes
    ($counter_name:ident, $count:expr) => {
        #[allow(unused_unsafe)]
        {
            unsafe { $crate::stats::COUNTERS.$counter_name += $count as u64 }
        }
    };
}
pub(crate) use incr_counter_by;

/// Macro to increment a counter by name
macro_rules! incr_counter {
    // Unsafe is ok here because options are initialized
    // once before any Ruby code executes
    ($counter_name:ident) => {
        #[allow(unused_unsafe)]
        {
            unsafe { $crate::stats::COUNTERS.$counter_name += 1 }
        }
    };
}
pub(crate) use incr_counter;

/// Macro to get a raw pointer to a given counter
macro_rules! ptr_to_counter {
    ($counter_name:ident) => {
        unsafe {
            let ctr_ptr = std::ptr::addr_of_mut!(COUNTERS.$counter_name);
            ctr_ptr
        }
    };
}
pub(crate) use ptr_to_counter;

// Declare all the counters we track
make_counters! {
    exec_instruction,

    send_keywords,
    send_klass_megamorphic,
    send_kw_splat,
    send_args_splat_super,
    send_iseq_zsuper,
    send_block_arg,
    send_ivar_set_method,
    send_zsuper_method,
    send_undef_method,
    send_optimized_method,
    send_optimized_method_call,
    send_optimized_method_block_call,
    send_call_block,
    send_call_kwarg,
    send_call_multi_ractor,
    send_missing_method,
    send_refined_method,
    send_cfunc_ruby_array_varg,
    send_cfunc_argc_mismatch,
    send_cfunc_toomany_args,
    send_cfunc_tracing,
    send_cfunc_kwargs,
    send_cfunc_splat_with_kw,
    send_cfunc_splat_send,
    send_attrset_kwargs,
    send_iseq_tailcall,
    send_iseq_arity_error,
    send_iseq_only_keywords,
    send_iseq_kwargs_req_and_opt_missing,
    send_iseq_kwargs_mismatch,
    send_iseq_has_post,
    send_iseq_has_kwrest,
    send_iseq_has_no_kw,
    send_iseq_accepts_no_kwarg,
    send_iseq_materialized_block,
    send_iseq_splat_with_opt,
    send_iseq_splat_with_kw,
    send_iseq_missing_optional_kw,
    send_iseq_too_many_kwargs,
    send_not_implemented_method,
    send_getter_arity,
    send_se_cf_overflow,
    send_se_protected_check_failed,
    send_splatarray_length_not_equal,
    send_splatarray_last_ruby_2_keywords,
    send_splat_not_array,
    send_args_splat_non_iseq,
    send_args_splat_ivar,
    send_args_splat_attrset,
    send_args_splat_bmethod,
    send_args_splat_aref,
    send_args_splat_aset,
    send_args_splat_opt_call,
    send_args_splat_cfunc_var_args,
    send_args_splat_cfunc_zuper,
    send_args_splat_cfunc_ruby2_keywords,
    send_iseq_splat_arity_error,
    send_iseq_ruby2_keywords,
    send_send_not_imm,
    send_send_wrong_args,
    send_send_null_mid,
    send_send_null_cme,
    send_send_nested,
    send_send_chain,
    send_send_chain_string,
    send_send_chain_not_string,
    send_send_chain_not_sym,
    send_send_chain_not_string_or_sym,
    send_send_getter,
    send_send_builtin,
    send_iseq_has_rest_and_captured,
    send_iseq_has_rest_and_send,
    send_iseq_has_rest_and_kw_supplied,
    send_iseq_has_rest_opt_and_block,
    send_iseq_has_rest_and_splat_not_equal,
    send_is_a_class_mismatch,
    send_instance_of_class_mismatch,
    send_interrupted,
    send_not_fixnums,
    send_not_string,
    send_mid_mismatch,

    send_bmethod_ractor,
    send_bmethod_block_arg,

    traced_cfunc_return,

    invokesuper_me_changed,
    invokesuper_block,

    invokeblock_none,
    invokeblock_iseq_arg0_has_kw,
    invokeblock_iseq_arg0_args_splat,
    invokeblock_iseq_arg0_not_array,
    invokeblock_iseq_arg0_wrong_len,
    invokeblock_iseq_block_changed,
    invokeblock_tag_changed,
    invokeblock_ifunc_args_splat,
    invokeblock_ifunc_kw_splat,
    invokeblock_proc,
    invokeblock_symbol,

    leave_se_interrupt,
    leave_interp_return,

    getivar_se_self_not_heap,
    getivar_idx_out_of_range,
    getivar_megamorphic,
    getivar_not_heap,

    setivar_se_self_not_heap,
    setivar_idx_out_of_range,
    setivar_val_heapobject,
    setivar_name_not_mapped,
    setivar_not_heap,
    setivar_frozen,
    setivar_megamorphic,

    definedivar_not_heap,
    definedivar_megamorphic,

    setlocal_wb_required,

    opt_plus_overflow,
    opt_minus_overflow,

    opt_mod_zero,
    opt_div_zero,

    opt_aref_argc_not_one,
    opt_aref_arg_not_fixnum,
    opt_aref_not_array,
    opt_aref_not_hash,

    opt_aset_not_array,
    opt_aset_not_fixnum,
    opt_aset_not_hash,

    opt_case_dispatch_megamorphic,

    opt_getinlinecache_miss,

    expandarray_splat,
    expandarray_postarg,
    expandarray_not_array,
    expandarray_rhs_too_small,

    gbp_wb_required,
    gbpp_block_param_modified,
    gbpp_block_handler_not_none,
    gbpp_block_handler_not_iseq,

    branchif_interrupted,
    branchunless_interrupted,
    branchnil_interrupted,
    jump_interrupted,

    objtostring_not_string,

    binding_allocations,
    binding_set,

    vm_insns_count,
    compiled_iseq_count,
    compiled_blockid_count,
    compiled_block_count,
    compiled_branch_count,
    compilation_failure,
    block_next_count,
    defer_count,
    defer_empty_count,
    branch_insn_count,
    branch_known_count,

    freed_iseq_count,

    exit_from_branch_stub,

    invalidation_count,
    invalidate_method_lookup,
    invalidate_bop_redefined,
    invalidate_ractor_spawn,
    invalidate_constant_state_bump,
    invalidate_constant_ic_fill,

    constant_state_bumps,

    // Not using "getivar_" to exclude this from exit reasons
    get_ivar_max_depth,

    // Currently, it's out of the ordinary (might be impossible) for YJIT to leave gaps in
    // executable memory, so this should be 0.
    exec_mem_non_bump_alloc,

    num_gc_obj_refs,

    num_send,
    num_send_known_class,
    num_send_polymorphic,
    num_send_x86_rel32,
    num_send_x86_reg,

    iseq_stack_too_large,
    iseq_too_long,

    temp_reg_opnd,
    temp_mem_opnd,
    temp_spill,
}

//===========================================================================

/// Primitive called in yjit.rb
/// Check if stats generation is enabled
#[no_mangle]
pub extern "C" fn rb_yjit_stats_enabled_p(_ec: EcPtr, _ruby_self: VALUE) -> VALUE {

    if get_option!(gen_stats) {
        return Qtrue;
    } else {
        return Qfalse;
    }
}

/// Primitive called in yjit.rb.
/// Export all YJIT statistics as a Ruby hash.
#[no_mangle]
pub extern "C" fn rb_yjit_get_stats(_ec: EcPtr, _ruby_self: VALUE, context: VALUE) -> VALUE {
    with_vm_lock(src_loc!(), || rb_yjit_gen_stats_dict(context == Qtrue))
}

/// Primitive called in yjit.rb
///
/// Check if trace_exits generation is enabled. Requires the stats feature
/// to be enabled.
#[no_mangle]
pub extern "C" fn rb_yjit_trace_exit_locations_enabled_p(_ec: EcPtr, _ruby_self: VALUE) -> VALUE {
    #[cfg(feature = "stats")]
    if get_option!(gen_trace_exits) {
        return Qtrue;
    }

    return Qfalse;
}

/// Call the C function to parse the raw_samples and line_samples
/// into raw, lines, and frames hash for RubyVM::YJIT.exit_locations.
#[no_mangle]
pub extern "C" fn rb_yjit_get_exit_locations(_ec: EcPtr, _ruby_self: VALUE) -> VALUE {
    // Return if YJIT is not enabled
    if !yjit_enabled_p() {
        return Qnil;
    }

    // Return if the stats feature is disabled
    if !cfg!(feature = "stats") {
        return Qnil;
    }

    // Return if --yjit-trace-exits isn't enabled
    if !get_option!(gen_trace_exits) {
        return Qnil;
    }

    // If the stats feature is enabled, pass yjit_raw_samples and yjit_line_samples
    // to the C function called rb_yjit_exit_locations_dict for parsing.
    let yjit_raw_samples = YjitExitLocations::get_raw_samples();
    let yjit_line_samples = YjitExitLocations::get_line_samples();

    // Assert that the two Vec's are the same length. If they aren't
    // equal something went wrong.
    assert_eq!(yjit_raw_samples.len(), yjit_line_samples.len());

    // yjit_raw_samples and yjit_line_samples are the same length so
    // pass only one of the lengths in the C function.
    let samples_len = yjit_raw_samples.len() as i32;

    unsafe {
        rb_yjit_exit_locations_dict(yjit_raw_samples.as_mut_ptr(), yjit_line_samples.as_mut_ptr(), samples_len)
    }
}

/// Export all YJIT statistics as a Ruby hash.
fn rb_yjit_gen_stats_dict(context: bool) -> VALUE {
    // If YJIT is not enabled, return Qnil
    if !yjit_enabled_p() {
        return Qnil;
    }

    macro_rules! hash_aset_usize {
        ($hash:ident, $counter_name:expr, $value:expr) => {
            let key = rust_str_to_sym($counter_name);
            let value = VALUE::fixnum_from_usize($value);
            rb_hash_aset($hash, key, value);
        }
    }

    let hash = unsafe { rb_hash_new() };

    // CodeBlock stats
    unsafe {
        // Get the inline and outlined code blocks
        let cb = CodegenGlobals::get_inline_cb();
        let ocb = CodegenGlobals::get_outlined_cb();

        // Inline code size
        hash_aset_usize!(hash, "inline_code_size", cb.code_size());

        // Outlined code size
        hash_aset_usize!(hash, "outlined_code_size", ocb.unwrap().code_size());

        // GCed pages
        let freed_page_count = cb.num_freed_pages();
        hash_aset_usize!(hash, "freed_page_count", freed_page_count);

        // GCed code size
        hash_aset_usize!(hash, "freed_code_size", freed_page_count * cb.page_size());

        // Live pages
        hash_aset_usize!(hash, "live_page_count", cb.num_mapped_pages() - freed_page_count);

        // Code GC count
        hash_aset_usize!(hash, "code_gc_count", CodegenGlobals::get_code_gc_count());

        // Size of memory region allocated for JIT code
        hash_aset_usize!(hash, "code_region_size", cb.mapped_region_size());

        // Rust global allocations in bytes
        #[cfg(feature="stats")]
        hash_aset_usize!(hash, "yjit_alloc_size", global_allocation_size());

        // `context` is true at RubyVM::YJIT._print_stats for --yjit-stats. It's false by default
        // for RubyVM::YJIT.runtime_stats because counting all Contexts could be expensive.
        if context {
            let live_context_count = get_live_context_count();
            let context_size = std::mem::size_of::<Context>();
            hash_aset_usize!(hash, "live_context_count", live_context_count);
            hash_aset_usize!(hash, "live_context_size", live_context_count * context_size);
        }
    }

    // If we're not generating stats, the hash is done
    if !get_option!(gen_stats) {
        return hash;
    }

    // If the stats feature is enabled

    unsafe {
        // Indicate that the complete set of stats is available
        rb_hash_aset(hash, rust_str_to_sym("all_stats"), Qtrue);

        // For each counter we track
        for counter_name in COUNTER_NAMES {
            // Get the counter value
            let counter_ptr = get_counter_ptr(counter_name);
            let counter_val = *counter_ptr;

            #[cfg(not(feature = "stats"))]
            if counter_name == &"vm_insns_count" {
                // If the stats feature is disabled, we don't have vm_insns_count
                // so we are going to exclude the key
                continue;
            }

            // Put counter into hash
            let key = rust_str_to_sym(counter_name);
            let value = VALUE::fixnum_from_usize(counter_val as usize);
            rb_hash_aset(hash, key, value);
        }

        // For each entry in exit_op_count, add a stats entry with key "exit_INSTRUCTION_NAME"
        // and the value is the count of side exits for that instruction.
        for op_idx in 0..VM_INSTRUCTION_SIZE_USIZE {
            let op_name = insn_name(op_idx);
            let key_string = "exit_".to_owned() + &op_name;
            let key = rust_str_to_sym(&key_string);
            let value = VALUE::fixnum_from_usize(EXIT_OP_COUNT[op_idx] as usize);
            rb_hash_aset(hash, key, value);
        }
    }

    hash
}

fn get_live_context_count() -> usize {
    let mut count = 0;
    for_each_iseq_payload(|iseq_payload| {
        for blocks in iseq_payload.version_map.iter() {
            for block in blocks.iter() {
                count += unsafe { block.as_ref() }.get_ctx_count();
            }
        }
        for block in iseq_payload.dead_blocks.iter() {
            count += unsafe { block.as_ref() }.get_ctx_count();
        }
    });
    count
}

/// Record the backtrace when a YJIT exit occurs. This functionality requires
/// that the stats feature is enabled as well as the --yjit-trace-exits option.
///
/// This function will fill two Vec's in YjitExitLocations to record the raw samples
/// and line samples. Their length should be the same, however the data stored in
/// them is different.
#[no_mangle]
pub extern "C" fn rb_yjit_record_exit_stack(exit_pc: *const VALUE)
{
    // Return if YJIT is not enabled
    if !yjit_enabled_p() {
        return;
    }

    // Return if the stats feature is disabled
    if !cfg!(feature = "stats") {
        return;
    }

    // Return if --yjit-trace-exits isn't enabled
    if !get_option!(gen_trace_exits) {
        return;
    }

    if get_option!(trace_exits_sample_rate) > 0 {
        if get_option!(trace_exits_sample_rate) <= *YjitExitLocations::get_skipped_samples() {
            YjitExitLocations::get_instance().skipped_samples = 0;
        } else {
            YjitExitLocations::get_instance().skipped_samples += 1;
            return;
        }
    }

    // rb_vm_insn_addr2opcode won't work in cargo test --all-features
    // because it's a C function. Without insn call, this function is useless
    // so wrap the whole thing in a not test check.
    if cfg!(not(test)) {
        // Get the opcode from the encoded insn handler at this PC
        let insn = unsafe { rb_vm_insn_addr2opcode((*exit_pc).as_ptr()) };

        // Use the same buffer size as Stackprof.
        const BUFF_LEN: usize = 2048;

        // Create 2 array buffers to be used to collect frames and lines.
        let mut frames_buffer = [VALUE(0_usize); BUFF_LEN];
        let mut lines_buffer = [0; BUFF_LEN];

        // Records call frame and line information for each method entry into two
        // temporary buffers. Returns the number of times we added to the buffer (ie
        // the length of the stack).
        //
        // Call frame info is stored in the frames_buffer, line number information
        // in the lines_buffer. The first argument is the start point and the second
        // argument is the buffer limit, set at 2048.
        let stack_length = unsafe { rb_profile_frames(0, BUFF_LEN as i32, frames_buffer.as_mut_ptr(), lines_buffer.as_mut_ptr()) };
        let samples_length = (stack_length as usize) + 3;

        let yjit_raw_samples = YjitExitLocations::get_raw_samples();
        let yjit_line_samples = YjitExitLocations::get_line_samples();

        // If yjit_raw_samples is less than or equal to the current length of the samples
        // we might have seen this stack trace previously.
        if yjit_raw_samples.len() >= samples_length {
            let prev_stack_len_index = yjit_raw_samples.len() - samples_length;
            let prev_stack_len = i64::from(yjit_raw_samples[prev_stack_len_index]);
            let mut idx = stack_length - 1;
            let mut prev_frame_idx = 0;
            let mut seen_already = true;

            // If the previous stack length and current stack length are equal,
            // loop and compare the current frame to the previous frame. If they are
            // not equal, set seen_already to false and break out of the loop.
            if prev_stack_len == stack_length as i64 {
                while idx >= 0 {
                    let current_frame = frames_buffer[idx as usize];
                    let prev_frame = yjit_raw_samples[prev_stack_len_index + prev_frame_idx + 1];

                    // If the current frame and previous frame are not equal, set
                    // seen_already to false and break out of the loop.
                    if current_frame != prev_frame {
                        seen_already = false;
                        break;
                    }

                    idx -= 1;
                    prev_frame_idx += 1;
                }

                // If we know we've seen this stack before, increment the counter by 1.
                if seen_already {
                    let prev_idx = yjit_raw_samples.len() - 1;
                    let prev_count = i64::from(yjit_raw_samples[prev_idx]);
                    let new_count = prev_count + 1;

                    yjit_raw_samples[prev_idx] = VALUE(new_count as usize);
                    yjit_line_samples[prev_idx] = new_count as i32;

                    return;
                }
            }
        }

        yjit_raw_samples.push(VALUE(stack_length as usize));
        yjit_line_samples.push(stack_length);

        let mut idx = stack_length - 1;

        while idx >= 0 {
            let frame = frames_buffer[idx as usize];
            let line = lines_buffer[idx as usize];

            yjit_raw_samples.push(frame);
            yjit_line_samples.push(line);

            idx -= 1;
        }

        // Push the insn value into the yjit_raw_samples Vec.
        yjit_raw_samples.push(VALUE(insn as usize));

        // We don't know the line
        yjit_line_samples.push(0);

        // Push number of times seen onto the stack, which is 1
        // because it's the first time we've seen it.
        yjit_raw_samples.push(VALUE(1_usize));
        yjit_line_samples.push(1);
    }
}

/// Primitive called in yjit.rb. Zero out all the counters.
#[no_mangle]
pub extern "C" fn rb_yjit_reset_stats_bang(_ec: EcPtr, _ruby_self: VALUE) -> VALUE {
    unsafe {
        EXIT_OP_COUNT = [0; VM_INSTRUCTION_SIZE_USIZE];
        COUNTERS = Counters::default();
    }

    return Qnil;
}

/// Increment the number of instructions executed by the interpreter
#[no_mangle]
pub extern "C" fn rb_yjit_collect_vm_usage_insn() {
    incr_counter!(vm_insns_count);
}

#[no_mangle]
pub extern "C" fn rb_yjit_collect_binding_alloc() {
    incr_counter!(binding_allocations);
}

#[no_mangle]
pub extern "C" fn rb_yjit_collect_binding_set() {
    incr_counter!(binding_set);
}

#[no_mangle]
pub extern "C" fn rb_yjit_count_side_exit_op(exit_pc: *const VALUE) -> *const VALUE {
    #[cfg(not(test))]
    unsafe {
        // Get the opcode from the encoded insn handler at this PC
        let opcode = rb_vm_insn_addr2opcode((*exit_pc).as_ptr());

        // Increment the exit op count for this opcode
        EXIT_OP_COUNT[opcode as usize] += 1;
    };

    // This function must return exit_pc!
    return exit_pc;
}

// Get the size of global allocations in Rust.
#[cfg(feature="stats")]
fn global_allocation_size() -> usize {
    let stats = GLOBAL_ALLOCATOR.stats();
    stats.bytes_allocated.saturating_sub(stats.bytes_deallocated)
}