ZJIT: Expose --zjit-recompile-cap option

Replace the hardcoded MAX_GLOBAL_RECOMPILATIONS constant with a
configurable --zjit-recompile-cap CLI option (default: 50, 0=unlimited).
This limits how many ISEQs can be recompiled per process, preventing
code size inflation on large workloads where many ISEQs hit the
side-exit threshold.

Author: nmeans

zjit/src/codegen.rs

@@ -51,7 +51,6 @@ pub extern "C" fn rb_zjit_count_side_exit(payload_raw: *mut std::ffi::c_void) {
 }
 
 static GLOBAL_RECOMPILE_COUNT: AtomicU64 = AtomicU64::new(0);
-const MAX_GLOBAL_RECOMPILATIONS: u64 = 50;
 
 /// Escalating threshold for deferred re-profiling. Higher deferral levels
 /// give cold branches progressively more time to warm up.
@@ -66,10 +65,13 @@ fn deferred_threshold(defer_count: u32) -> u32 {
 /// When `preserve_profiles` is true, only counters are reset (type distributions survive).
 /// When false, both counters and type distributions are cleared.
 fn trigger_recompilation(payload_raw: *mut std::ffi::c_void, iseq: IseqPtr, preserve_profiles: bool) {
-    if MAX_GLOBAL_RECOMPILATIONS > 0 {
+    // Global recompilation cap: prevent code size inflation and overhead from
+    // too many ISEQs recompiling. Configurable via --zjit-recompile-cap=num.
+    let cap = get_option!(recompile_cap);
+    if cap > 0 {
         let prev = GLOBAL_RECOMPILE_COUNT.fetch_add(1, Ordering::Relaxed);
-        if prev >= MAX_GLOBAL_RECOMPILATIONS {
-            GLOBAL_RECOMPILE_COUNT.fetch_sub(1, Ordering::Relaxed);
+        if prev >= cap {
+            GLOBAL_RECOMPILE_COUNT.fetch_sub(1, Ordering::Relaxed); // undo increment
             return;
         }
     }

zjit/src/options.rs

@@ -103,6 +103,10 @@ pub struct Options {
     /// Number of side exits before triggering recompilation of an ISEQ.
     /// Set to 0 to disable recompilation.
     pub recompile_threshold: u64,
+
+    /// Maximum number of ISEQs that can be recompiled per process.
+    /// Limits code size inflation for large workloads. Set to 0 for unlimited.
+    pub recompile_cap: u64,
 }
 
 impl Default for Options {
@@ -129,6 +133,7 @@ impl Default for Options {
             allowed_iseqs: None,
             log_compiled_iseqs: None,
             recompile_threshold: DEFAULT_RECOMPILE_THRESHOLD,
+            recompile_cap: 50,
         }
     }
 }
@@ -154,6 +159,8 @@ pub const ZJIT_OPTIONS: &[(&str, &str)] = &[
                      "Log compiled ISEQs to the file. The file will be truncated."),
     ("--zjit-recompile-threshold=num",
                      "Side exits to trigger recompile (default: 100, 0=off)."),
+    ("--zjit-recompile-cap=num",
+                     "Max ISEQs to recompile (default: 50, 0=unlimited)."),
     ("--zjit-trace-exits[=counter]",
                      "Record source on side-exit. `Counter` picks specific counter."),
     ("--zjit-trace-exits-sample-rate=num",
@@ -348,6 +355,13 @@ fn parse_option(str_ptr: *const std::os::raw::c_char) -> Option<()> {
             Err(_) => return None,
         },
 
+        ("recompile-cap", _) => match opt_val.parse() {
+            Ok(n) => {
+                options.recompile_cap = n;
+            }
+            Err(_) => return None,
+        },
+
         ("stats-quiet", _) => {
             options.stats = true;
             options.print_stats = false;