From 4b61f589fd66370bce28b9bc054aed4ec674a706 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Nils=20O=2E=20Sel=C3=A5sdal?= <nos@utel.tech>
Date: Tue, 16 Jun 2026 23:53:30 +0200
Subject: [PATCH] Refactor decommit to arena_trim

---
 src/arena.c | 19 +++++++++++++------
 src/arena.h |  2 ++
 2 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/src/arena.c b/src/arena.c
index 3ca6661..2acbe07 100644
--- a/src/arena.c
+++ b/src/arena.c
@@ -128,12 +128,7 @@ void arena_reset_to(Arena *arena, U64 total_offset)
             ASAN_POISON_MEMORY_REGION(&block->base[block->first_free], memoryblock_available(block));
 
             if ((arena->flags & ArenaFlag_NoDecommit) == 0) {
-                U32 aligned_pos = RoundUpToMultiple(block->first_free, arena->commit_size);
-                if (aligned_pos < block->committed_end) {
-                    ASAN_UNPOISON_MEMORY_REGION(&block->base[aligned_pos], block->committed_end);
-                    memory_decommit(&block->base[aligned_pos], block->committed_end - aligned_pos);
-                    block->committed_end = aligned_pos;
-                }
+                arena_trim(arena);
             }
 
             break;
@@ -143,6 +138,18 @@ void arena_reset_to(Arena *arena, U64 total_offset)
     }
 }
 
+void arena_trim(Arena *arena)
+{
+    MemoryBlock *block = arena->current;
+    U32 aligned_pos = RoundUpToMultiple(block->first_free, arena->commit_size);
+    if (aligned_pos < block->committed_end) {
+        void *trim_start = &block->base[aligned_pos];
+        // Note(nos): Should we unpoision ?
+        //ASAN_UNPOISON_MEMORY_REGION(trim_start, block->committed_end);
+        memory_decommit(trim_start, block->committed_end - aligned_pos);
+        block->committed_end = aligned_pos;
+    }
+            }
 ATemp arena_temp_begin(Arena *arena)
 {
     ATemp checkpoint = {};
diff --git a/src/arena.h b/src/arena.h
index f2f64db..638ae11 100644
--- a/src/arena.h
+++ b/src/arena.h
@@ -54,6 +54,8 @@ void *arena_push(Arena *arena, U32 size, U32 align);
 // Invalid for arrays > U32
 #define arena_push_array_of(arena, type, len) arena_push(arena, (U32) (sizeof(type) * (len)), alignof(type))
 
+void arena_trim(Arena *arena);
+
 ATemp arena_temp_begin(Arena *arena);
 void arena_temp_end(ATemp *checkpoint);
 void arena_reset_to(Arena *arena, U64 total_offset);