From fa154f6944ce6b104e62702b3ccc31985ab29566 Mon Sep 17 00:00:00 2001
From: Jorge Prendes <jorge.prendes@gmail.com>
Date: Thu, 25 Sep 2025 16:32:18 +0100
Subject: [PATCH] Fix large allocations in preallocated arenas

Signed-off-by: Jorge Prendes <jorge.prendes@gmail.com>
---
 CMakeLists.txt                |  2 +-
 src/bitmap.c                  |  2 --
 test/CMakeLists.txt           |  4 ++++
 test/test-large-arena-alloc.c | 30 ++++++++++++++++++++++++++++++
 4 files changed, 35 insertions(+), 3 deletions(-)
 create mode 100644 test/test-large-arena-alloc.c

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 5ce084f6..a56197d6 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -708,7 +708,7 @@ if (MI_BUILD_TESTS)
   enable_testing()
 
   # static link tests
-  foreach(TEST_NAME api api-fill stress)
+  foreach(TEST_NAME api api-fill stress large-arena-alloc)
     add_executable(mimalloc-test-${TEST_NAME} test/test-${TEST_NAME}.c)
     target_compile_definitions(mimalloc-test-${TEST_NAME} PRIVATE ${mi_defines})
     target_compile_options(mimalloc-test-${TEST_NAME} PRIVATE ${mi_cflags})
diff --git a/src/bitmap.c b/src/bitmap.c
index 32d1e954..9e07d9cb 100644
--- a/src/bitmap.c
+++ b/src/bitmap.c
@@ -304,13 +304,11 @@ bool _mi_bitmap_try_find_from_claim_across(mi_bitmap_t bitmap, const size_t bitm
   for (size_t visited = 0; visited < bitmap_fields; visited++, idx++) {
     if (idx >= bitmap_fields) { idx = 0; } // wrap
     // first try to claim inside a field
-    /*
     if (count <= MI_BITMAP_FIELD_BITS) {
       if (_mi_bitmap_try_find_claim_field(bitmap, idx, count, bitmap_idx)) {
         return true;
       }
     }
-    */
     // if that fails, then try to claim across fields
     if (mi_bitmap_try_find_claim_field_across(bitmap, bitmap_fields, idx, count, 0, bitmap_idx)) {
       return true;
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index c5fff1a6..72b2d0b0 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -54,3 +54,7 @@ target_link_libraries(static-override-cxx PUBLIC mimalloc-static)
 ## test memory errors
 add_executable(test-wrong  test-wrong.c)
 target_link_libraries(test-wrong PUBLIC mimalloc)
+
+## test large memory allocations in a preallocated arena
+add_executable(test-large-arena-alloc  test-large-arena-alloc.c)
+target_link_libraries(test-large-arena-alloc PUBLIC mimalloc)
diff --git a/test/test-large-arena-alloc.c b/test/test-large-arena-alloc.c
new file mode 100644
index 00000000..47b48dc8
--- /dev/null
+++ b/test/test-large-arena-alloc.c
@@ -0,0 +1,30 @@
+// Issue #1142: Test that allocating large amounts of memory (3+ bits in the bitmap)
+// uses the preallocated arena when a large enough arena is provided.
+#include <stdio.h>
+#include <mimalloc.h>
+
+#define ARENA_SIZE (256 * 1024 * 1024)
+#define ALLOC_SIZE (64 * 1024 * 1024)
+
+char memory[ARENA_SIZE] = {0};
+
+int main(void) {
+  mi_option_set_enabled(mi_option_disallow_os_alloc, true);
+  mi_option_set_enabled(mi_option_verbose, true);
+
+  mi_manage_os_memory(
+    memory,
+    sizeof(memory),
+    1 /* committed */,
+    0 /* large     */,
+    0 /* zero      */,
+    -1 /* numa_node */
+  );
+
+  void * ptr = mi_malloc(ALLOC_SIZE);
+
+  fprintf(stderr, "ptr = %p\n", ptr);
+
+  mi_option_set_enabled(mi_option_verbose, false);
+  return ptr ? 0 : 1;
+}
\ No newline at end of file