From a7d0265480c662964988f83d4e245bf139eb7cc0 Mon Sep 17 00:00:00 2001
From: Mike Pall <mike>
Date: Thu, 28 Jul 2022 15:40:28 +0200
Subject: Improve GC estimation for userdata with attached managed memory.

This works well for string.buffers, but not for userdata or
cdata with attached unmanaged memory (malloc/free, mmap/munmap).
---
 src/lj_gc.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/lj_gc.c b/src/lj_gc.c
index b35a0d44..2fc52ec1 100644
--- a/src/lj_gc.c
+++ b/src/lj_gc.c
@@ -700,9 +700,12 @@ static size_t gc_onestep(lua_State *L)
     }
   case GCSfinalize:
     if (gcref(g->gc.mmudata) != NULL) {
+      GCSize old = g->gc.total;
       if (tvref(g->jit_base))  /* Don't call finalizers on trace. */
 	return LJ_MAX_MEM;
       gc_finalize(L);  /* Finalize one userdata object. */
+      if (old >= g->gc.total && g->gc.estimate > old - g->gc.total)
+	g->gc.estimate -= old - g->gc.total;
       if (g->gc.estimate > GCFINALIZECOST)
 	g->gc.estimate -= GCFINALIZECOST;
       return GCFINALIZECOST;
-- 
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