Update yjit.md

Update some out of date information and mention how to check that YJIT is enabled.

doc/yjit/yjit.md

@@ -157,8 +157,8 @@ YJIT supports all command-line options supported by upstream CRuby, but also add
 
 - `--yjit`: enable YJIT (disabled by default)
 - `--yjit-call-threshold=N`: number of calls after which YJIT begins to compile a function (default 30)
-- `--yjit-exec-mem-size=N`: size of the executable memory block to allocate, in MiB (default 128 MiB)
+- `--yjit-exec-mem-size=N`: size of the executable memory block to allocate, in MiB (default 64 MiB)
-- `--yjit-stats`: produce statistics after the execution of a program
+- `--yjit-stats`: produce statistics after the execution of a program (incurs a run-time cost)
 - `--yjit-trace-exits`: produce a Marshal dump of backtraces from specific exits. Automatically enables `--yjit-stats` (must configure and build with `--enable-yjit=stats` to use this)
 - `--yjit-max-versions=N`: maximum number of versions to generate per basic block (default 4)
 - `--yjit-greedy-versioning`: greedy versioning mode (disabled by default, may increase code size)
@@ -166,6 +166,13 @@ YJIT supports all command-line options supported by upstream CRuby, but also add
 Note that there is also an environment variable `RUBY_YJIT_ENABLE` which can be used to enable YJIT.
 This can be useful for some deployment scripts where specifying an extra command-line option to Ruby is not practical.
 
+You can verify that YJIT is enabled by checking that `ruby -v --yjit` includes the string `+YJIT`:
+
+```sh
+ruby -v --yjit
+ruby 3.3.0dev (2023-01-31T15:11:10Z master 2a0bf269c9) +YJIT dev [x86_64-darwin22]
+```
+
 ### Benchmarking
 
 We have collected a set of benchmarks and implemented a simple benchmarking harness in the [yjit-bench](https://github.com/Shopify/yjit-bench) repository. This benchmarking harness is designed to disable CPU frequency scaling, set process affinity and disable address space randomization so that the variance between benchmarking runs will be as small as possible. Please kindly note that we are at an early stage in this project.
@@ -245,8 +252,6 @@ The YJIT source code is divided between:
 - `yjit/src/options.rs`: handling of command-line options
 - `yjit/bindgen/src/main.rs`: C bindings exposed to the Rust codebase through bindgen
 - `yjit/src/cruby.rs`: C bindings manually exposed to the Rust codebase
-- `misc/test_yjit_asm.sh`: script to compile and run the in-memory assembler tests
-- `misc/yjit_asm_tests.c`: tests for the in-memory assembler
 
 The core of CRuby's interpreter logic is found in:
 - `insns.def`: defines Ruby's bytecode instructions (gets compiled into `vm.inc`)