mm: fix/improve malloc for on-demand paging

src/mm/user_heap/umm_malloc.cc

@@ -7,39 +7,52 @@
 #include "common/logger.h"
 #include "mm/pgtable.h"
 
-// FIXME
-#define PAGING_PAGES (static_cast<uint64_t>(1024) * 1024 * 1024 * 2 / PAGE_SIZE)
-
 namespace evisor {
 
 namespace {
+// FIXME: use kUserSize
+constexpr uint32_t kPagingPages =
+    static_cast<uint64_t>(1024) * 1024 * 1024 * 2 / PAGE_SIZE;
+constexpr uint32_t kMemMapSize = kPagingPages / 8;
 
-bool userHeapMemMap[PAGING_PAGES] = {false};
-
+uint8_t userMemoryRegionMap_[kPagingPages] = {0};
+uint32_t nextFreeSpaceIndex = 0;
 }  // namespace
 
 void* umm_malloc(size_t size) {
-  if (size < 1) {
+  if (size < PAGE_SIZE) {
+    LOG_ERROR("Requested size (%d) is less than page size(%d)", size,
+              PAGE_SIZE);
     return nullptr;
   }
 
-  // FIXME
-  size = size;
+  if (size % PAGE_SIZE != 0) {
+    LOG_ERROR("Requested size (%d) is not aligned to page size(%d)", size,
+              PAGE_SIZE);
+    return nullptr;
+  }
 
-  for (uint32_t i = 0; i < PAGING_PAGES; i++) {
-    if (!userHeapMemMap[i]) {
-      userHeapMemMap[i] = true;
+  for (uint32_t i = nextFreeSpaceIndex; i < kPagingPages; i++) {
+    const uint32_t j = i / 8;
+    const uint8_t bit = 1 << (i % 8);
+    if ((userMemoryRegionMap_[j] & bit) == 0) {
+      userMemoryRegionMap_[j] |= bit;
+      nextFreeSpaceIndex = i + 1;
       auto* page = reinterpret_cast<uint64_t*>(kUserStart + i * PAGE_SIZE);
       return page;
     }
   }
-  PANIC("No free pages!");
+
+  PANIC("No free pages in user memory region!");
   return nullptr;
 }
 
 void umm_free(void* va) {
-  userHeapMemMap[(reinterpret_cast<uint64_t>(va) - kUserStart) / PAGE_SIZE] =
-      false;
+  const uint32_t page =
+      (reinterpret_cast<uint64_t>(va) - kUserStart) / PAGE_SIZE;
+  const uint32_t i = page / 8;
+  const uint8_t bit = 1 << (page % 8);
+  userMemoryRegionMap_[i] &= ~bit;
 }
 
 }  // namespace evisor