power-of-two kmalloc

should be much faster, though no more scalable

power-of-two kmalloc
41d63b70 · Robert Morris · a7b311ad · 41d63b70
--- a/kmalloc.c
+++ b/kmalloc.c
@@ -10,6 +10,106 @@
 #include "mtrace.h"
 #include "cpu.h"

+// allocate in power-of-two sizes up to 2^KMMAX
+// must be < 12
+#define KMMAX 11
+
+struct header {
+  struct header *next;
+};
+
+struct freelist {
+  struct header *buckets[KMMAX+1];
+  char name[MAXNAME];
+  struct spinlock lock;
+};
+
+struct freelist freelists[NCPU];
+
+void
+kminit(void)
+{
+  for (int c = 0; c < NCPU; c++) {
+    freelists[c].name[0] = (char) c + '0';
+    safestrcpy(freelists[c].name+1, "freelist", MAXNAME-1);
+    initlock(&freelists[c].lock, freelists[c].name);
+  }
+}
+
+// get more space for freelists[c].buckets[b]
+void
+morecore(int c, int b)
+{
+  char *p = kalloc();
+  if(p == 0)
+    return;
+
+  int sz = 1 << b;
+  for(char *q = p;
+      q + sz + sizeof(struct header) <= p + PGSIZE;
+      q += sz + sizeof(struct header)){
+    struct header *h = (struct header *) q;
+    h->next = freelists[c].buckets[b];
+    freelists[c].buckets[b] = h;
+  }
+}
+
+void *
+kmalloc(u64 nbytes)
+{
+  int nn = 1, b = 0;
+  void *r = 0;
+  struct header *h;
+  int c = mycpu()->id;
+
+  while(nn < nbytes && b <= KMMAX){
+    nn *= 2;
+    b++;
+  }
+  if(nn != (1 << b))
+    panic("kmalloc oops");
+  if(b > KMMAX)
+    panic("kmalloc too big");
+
+  acquire(&freelists[c].lock);
+  if(freelists[c].buckets[b] == 0)
+    morecore(c, b);
+  h = freelists[c].buckets[b];
+  if(h){
+    freelists[c].buckets[b] = h->next;
+    r = h + 1;
+    h->next = (void *) (long) b;
+  }
+  release(&freelists[c].lock);
+
+  if (r)
+    mtlabel(mtrace_label_heap, r, nbytes, "kmalloc'ed", sizeof("kmalloc'ed"));
+  if(r == 0)
+    cprintf("kmalloc(%d) failed\n", (int) nbytes);
+  return r;
+}
+
+void
+kmfree(void *ap)
+{
+  int c = mycpu()->id;
+  struct header *h;
+  int b;
+
+  acquire(&freelists[c].lock);
+
+  h = (struct header *) ((char *)ap - sizeof(struct header));
+  b = (long) h->next;
+  if(b < 0 || b > KMMAX)
+    panic("kmfree bad bucket");
+  h->next = freelists[c].buckets[b];
+  freelists[c].buckets[b] = h;
+
+  mtunlabel(mtrace_label_heap, ap);
+  release(&freelists[c].lock);
+}
+
+#if 0
 // Memory allocator by Kernighan and Ritchie,
 // The C programming Language, 2nd ed.  Section 8.7.

@@ -128,6 +228,8 @@ kmalloc(u64 nbytes)
  return r;
 }

+#endif
+
 int
 kmalign(void **p, int align, u64 size)
 {