From d1ace374b62fd083e0f8a6445a9fbd95d50a68bf Mon Sep 17 00:00:00 2001
From: Drew Galbraith <dgalbraith33@gmail.com>
Date: Fri, 24 Nov 2023 16:04:40 -0800
Subject: [PATCH] [Zion] Return freed kernel stacks to pool.

---
 zion/memory/kernel_stack_manager.cpp | 10 ++++++++--
 zion/memory/kernel_stack_manager.h   |  4 +++-
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/zion/memory/kernel_stack_manager.cpp b/zion/memory/kernel_stack_manager.cpp
index d7ec980..31ca839 100644
--- a/zion/memory/kernel_stack_manager.cpp
+++ b/zion/memory/kernel_stack_manager.cpp
@@ -15,6 +15,9 @@ void KernelStackManager::SetupInterruptStack() {
 }
 
 uint64_t KernelStackManager::AllocateKernelStack() {
+  if (!free_stacks_.empty()) {
+    return free_stacks_.PopFront();
+  }
   next_stack_addr_ += kKernelStackOffset;
   if (next_stack_addr_ >= kKernelStackEnd) {
     panic("No more kernel stack space");
@@ -24,6 +27,9 @@ uint64_t KernelStackManager::AllocateKernelStack() {
 }
 
 void KernelStackManager::FreeKernelStack(uint64_t stack_base) {
-  freed_stack_cnt_++;
-  dbgln("Freed kernel stacks using {} KiB", freed_stack_cnt_ * 12);
+  // TODO: Validate this value.
+  if ((stack_base & 0x3FF8) != 0x3FF8) {
+    dbgln("Odd kernel stack free {x}", stack_base);
+  }
+  free_stacks_.PushFront(stack_base);
 }
diff --git a/zion/memory/kernel_stack_manager.h b/zion/memory/kernel_stack_manager.h
index b331c92..3cd9187 100644
--- a/zion/memory/kernel_stack_manager.h
+++ b/zion/memory/kernel_stack_manager.h
@@ -1,5 +1,6 @@
 #pragma once
 
+#include <glacier/container/linked_list.h>
 #include <stdint.h>
 
 // KernelStackManager doles out kernel stacks.
@@ -24,5 +25,6 @@ class KernelStackManager {
 
  private:
   uint64_t next_stack_addr_;
-  uint64_t freed_stack_cnt_ = 0;
+
+  glcr::LinkedList<uint64_t> free_stacks_;
 };