kernel: minor malloc tweaks before refactor

* firstfreepage now updates properly, preventing a crash (oops)
* kfree only wipes the length of the allocation, not the entire page - which
  should make it easier to see the performance impact of the pagealloc changes

1 files changed, 14 insertions, 8 deletions

diff --git a/src/kernel/malloc.c b/src/kernel/malloc.c
index 471c945..0d5cba3 100644
--- a/src/kernel/malloc.c
+++ b/src/kernel/malloc.c
@@ -51,7 +51,7 @@ pbitmap_set(void *p, bool v)
 	assert(b < pbitmap_len);
 	bool prev = (pbitmap[b]&m) != 0;
 	if (v) {
-		pbitmap[b] |=  m;
+		pbitmap[b] |= m;
 	} else {
 		pbitmap[b] &= ~m;
 	}
@@ -83,9 +83,13 @@ mem_reserve(void *addr, size_t len)
 	void *top = min(addr + len, memtop);
 	addr = (void*)((uintptr_t)addr & ~PAGE_MASK); /* round down to page */
 	for (void *p = max(addr, (void*)pbitmap); p < top; p += PAGE_SIZE) {
+		/* this doesn't allow overlapping reserved regions, but, more
+		 * importantly, it prevents reserving an already allocated page */
+		if (pbitmap_get(p)) {
+			panic_invalid_state();
+		}
 		pbitmap_set(p, true);
 	}
-
 }
 
 void
@@ -147,6 +151,7 @@ page_free(void *addr, size_t pages)
 			panic_invalid_state();
 		}
 	}
+	firstfreepage = min(firstfreepage, addr);
 }
 
 static void
@@ -206,14 +211,13 @@ void
 kfree(void *ptr)
 {
 	Allocation *hdr;
-	size_t pages;
+	size_t len;
 	if (ptr == NULL) return;
 
-	hdr = ptr - sizeof(Allocation);
 	kmalloc_sanity(ptr);
-	pages = page_amt(hdr->len);
+	hdr = ptr - sizeof(Allocation);
+	len = hdr->len;
 
-	hdr->magic = ~MALLOC_MAGIC; // (hopefully) detect double frees
 	if (hdr->next)
 		hdr->next->prev = hdr->prev;
 	if (hdr->prev)
@@ -221,7 +225,9 @@ kfree(void *ptr)
 	if (malloc_last == hdr)
 		malloc_last = hdr->prev;
 #ifndef NDEBUG
-	memset(hdr, 0xC0, pages * PAGE_SIZE);
+	memset(hdr, 0xC0, len);
+#else
+	hdr->magic = ~MALLOC_MAGIC; /* (hopefully) detect double frees */
 #endif
-	page_free(hdr, pages);
+	page_free(hdr, page_amt(len));
 }