diff --git a/core/alloc.c b/core/alloc.c
index 1448334..fa466e7 100644
--- a/core/alloc.c
+++ b/core/alloc.c
@@ -11,32 +11,56 @@
 #define SLUB_SIZE (PAGE_SHIFT - 1)
 struct slabDesc *slub;
 
-int initSlabDesc(struct slabDesc **desc, size_t size);
+int addSlab(struct slabDesc **desc, size_t size);
 static int formatPage(struct slabDesc *desc, size_t size);
 
-int initSlab(void)
+int allocInit(void)
 {
         uint start = log2(sizeof(void *));
         list_init(slub);
         for (uint i = start; i < SLUB_SIZE; i++) {
-                struct slabDesc *slab;
-                if (initSlabDesc(&slab, 1U << i))
-                        return ENOMEM;
-                list_add_tail(slub, slab);
+                int ret;
+                if ((ret = allocBookSlab(1U << i))) {
+                        pr_devel("Fail to allocBookSlab %d\n", ret);
+                        return -ENOMEM;
+                }
         }
         return 0;
 }
 
-int initSlabDesc(struct slabDesc **desc, size_t size)
+int allocBookSlab(size_t size)
+{
+        struct slabDesc *slabEntry;
+        struct slabDesc *slab;
+        int slabIdx;
+        int ret;
+        if ((ret = addSlab(&slabEntry, size)))
+                return ret;
+        list_foreach(slub, slab, slabIdx)
+        {
+                if (slab->size == size) {
+                        pr_devel("Slab already exist");
+                        return -EEXIST;
+                }
+                if (slab->size > size) {
+                        list_insert_before(slub, slab, slabEntry);
+                        return 0;
+                }
+        }
+        list_add_tail(slub, slabEntry);
+        return 0;
+}
+
+int addSlab(struct slabDesc **desc, size_t size)
 {
         if (size > PAGE_SIZE)
-                return ENOENT;
+                return -ENOENT;
         paddr_t alloc = allocPhyPage();
         if (alloc == (paddr_t)NULL)
-                return ENOMEM;
-        if (pageMap((vaddr_t)alloc, alloc, PAGING_MEM_WRITE)) {
-                return ENOMEM;
-        }
+                return -ENOMEM;
+        if (pageMap((vaddr_t)alloc, alloc, PAGING_MEM_WRITE))
+                return -ENOMEM;
+
         *desc = (struct slabDesc *)alloc;
         list_singleton(*desc, *desc);
         (*desc)->page   = (vaddr_t)alloc;
@@ -64,7 +88,7 @@ static void *allocFromSlab(struct slabDesc *slab)
 {
         vaddr_t *next = slab->freeEl;
         if (*next == (vaddr_t)NULL) {
-                pr_devel("Slab %d full\n", slab);
+                pr_devel("Slab @%d for %d full\n", slab, slab->size);
                 slab->full = 1;
         } else {
                 slab->freeEl = (void *)(*next);
@@ -82,7 +106,7 @@ void *malloc(size_t size)
         uint slubIdx = 0;
         list_foreach(slub, slubEntry, slubIdx)
         {
-                if(size <= slubEntry->size)
+                if (size <= slubEntry->size)
                         break;
         }
         struct slabDesc *slab;
@@ -96,7 +120,11 @@ void *malloc(size_t size)
         }
         if (!list_foreach_early_break(slubEntry, slab, slabIdx)) {
                 struct slabDesc *newSlab;
-                initSlabDesc(&newSlab, slab->size);
+                int ret;
+                if ((ret = addSlab(&newSlab, slab->size))) {
+                        pr_devel("Fail to addSlab %d\n", ret);
+                        return NULL;
+                }
                 list_add_head(slubEntry, newSlab);
                 return allocFromSlab(newSlab);
         }
diff --git a/core/alloc.h b/core/alloc.h
index cbe1019..d644cd3 100644
--- a/core/alloc.h
+++ b/core/alloc.h
@@ -10,6 +10,7 @@ struct slabDesc {
         struct slabDesc *next;
         struct slabDesc *prev;
 };
-int initSlab(void);
+int allocInit(void);
+int allocBookSlab(size_t size);
 
 void *malloc(size_t size);
diff --git a/core/main.c b/core/main.c
index 15b7ca2..f119452 100644
--- a/core/main.c
+++ b/core/main.c
@@ -81,7 +81,7 @@ void kmain(unsigned long magic, unsigned long addr)
 
     printf("Setting up Serial link (115200)\n");
     serialSetup(115200);
-    initSlab();
+    allocInit();
 #ifdef RUN_TEST
     run_test();
 #endif
diff --git a/core/paging.c b/core/paging.c
index 8f44ae9..223073e 100644
--- a/core/paging.c
+++ b/core/paging.c
@@ -141,7 +141,7 @@ int pageMap(vaddr_t vaddr, paddr_t paddr, int flags)
 	if (!pd[pdEntry].present) {
 		paddr_t ptPhy = allocPhyPage();
 		if (ptPhy == (vaddr_t)NULL)
-			return ENOMEM;
+			return -ENOMEM;
 
 		pd[pdEntry].user    = (flags & PAGING_MEM_USER) ? 1 : 0;
 		pd[pdEntry].present = 1;