Little meta-alloc improvement.

1 files changed, 5 insertions, 3 deletions

diff --git a/src/zisp/gc/meta_alloc.zig b/src/zisp/gc/meta_alloc.zig
index 4dec92d..aa21967 100644
--- a/src/zisp/gc/meta_alloc.zig
+++ b/src/zisp/gc/meta_alloc.zig
@@ -476,9 +476,11 @@ export fn flush_thread_reserves() void {
         const tl = &tl_slab_infos[sci];
         const slab: *Slab = &slabs[sci];
 
-        // Just a rough check, assuming 4 KiB pages: If wm_hi - wm_lo >= 8 KiB,
-        // it means there's a minimum of one untouched page in between.
-        if (tl.wm_hi - tl.wm_lo > 8192 / @sizeOf(Unit)) {
+        // Given our chunked WM bumps and smallest size class, hi - lo > 4 KiB
+        // implies that there's at least one entire untouched page, as well as
+        // at least one >=128-byte slot before it, which can hold the metadata
+        // of the vacancy-list entry without faulting in an empty page.
+        if (tl.wm_hi - tl.wm_lo > 4096 / @sizeOf(Unit)) {
             flush_to_vl(info, tl, slab);
         }