From 7dfe547e1918ecbb15495e8e15af4d2567584997 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Nils=20O=2E=20Sel=C3=A5sdal?= <nos@utel.tech>
Date: Tue, 9 Jun 2026 02:05:50 +0200
Subject: [PATCH] Fix commit at block end

---
 src/arena.c |  3 ++-
 src/main.c  | 25 ++++++++++++++++++++++++-
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/src/arena.c b/src/arena.c
index fecfe81..dbbc3ed 100644
--- a/src/arena.c
+++ b/src/arena.c
@@ -25,7 +25,7 @@ MemoryBlock *memoryblock_allocate(size_t size, size_t commit_size)
 void arena_init(Arena *arena, const ArenaParams *params)
 {
     Assert(params->size > MemoryBlock_Header_Size);
-    Assert(params->size < (U32_Max -  Max(params->commit_size, platform_page_size()))); // Reserving last piece so our math doesn't overflow
+    Assert(params->size < (U32_Max -  platform_page_size())); // Reserving last piece so our math doesn't overflow
     Assert(IsPow2(params->commit_size));
 
     MemoryBlock *block = memoryblock_allocate(params->size, params->commit_size);
@@ -84,6 +84,7 @@ void *arena_push(Arena *arena, U32 size, U32 align)
         // Commit more memory
         U32 aligned_end_pos   = AlignToPageEnd(start_pos + size);
         U32 aligned_size      = RoundUpToMultiple(aligned_end_pos - block->committed_pos, arena->commit_size);
+        aligned_size = Min(aligned_size, block->size - block->committed_pos); // Note(nos): Is this actually right ?
 
         memory_commit(&block->base[block->committed_pos], aligned_size);
         block->committed_pos  += aligned_size;
diff --git a/src/main.c b/src/main.c
index 3f9c7fc..41de530 100644
--- a/src/main.c
+++ b/src/main.c
@@ -44,6 +44,7 @@ static void arena_test_1(void)
     arena_dump(&arena);
     arena_free(&arena);
 }
+
 static void arena_test_2(void)
 {
     ArenaParams arena_params = {};
@@ -92,8 +93,30 @@ static void arena_test_2(void)
     arena_free(&arena);
 }
 
+static void arena_test_3(void)
+{
+    ArenaParams arena_params = {};
+    U32 arena_size = KB(97) + MemoryBlock_Header_Size;
+    U32 commit_size = KB(32);
+    arena_params.size = arena_size;
+    arena_params.commit_size = commit_size;
+    Arena arena;
+    arena_init(&arena, &arena_params);
+    arena_dump(&arena);
+    void *ptr = arena_push(&arena, KB(64), 32);
+    MemoryZero(ptr, KB(64));
+    printf("Allocated ptr %p\n", ptr);
+    arena_dump(&arena);
+    ptr = arena_push(&arena, KB(97) - KB(64), 32);
+    MemoryZero(ptr, KB(97) - KB(64));
+    printf("Allocated ptr %p\n", ptr);
+    arena_dump(&arena);
+    arena_free(&arena);
+}
+
 int main(int argc, char *argv[])
 {
     //arena_test_1();
-    arena_test_2();
+    //arena_test_2();
+    arena_test_3();
 }