Summary: I think line 294 in kern_malloc.c can be deleted, and a tiny
bit of memory might be saved. L294 is the first of two lines that look
like:
offset = __VM_CACHELINE_ALIGN(offset);
I did a quick test to confirm it's okay to remove.
If you buy that, you can skip the rest of this email!
****
In more detail:
I can't see why line 294 is there. There's already code later in the
function to deal with the alignment issue, and it looks correct on its
own.
To test my theory, I deleted the line and added a bunch of kprintfs.
Result: no failed KKASSERTs, no crashes, and sometimes a malloc_slab
can store one more object than before.
****
In even more detail:
I booted a kernel with the following patch, which deletes line 294 and
adds a bunch of printfs. (The new function malloc_mgt_old_count is just
a copy of the old calculation, so I can show a comparison with
kprintf.)
Output of "dmesg|grep XXX" at bottom.
+static size_t malloc_mgt_old_count(size_t size)
+{
+ size_t offset;
+ size_t count;
+
+ /*
+ * Figure out the count by taking into account the size of the fobjs[]
+ * array by adding it to the object size.
+ */
+ offset = offsetof(struct kmalloc_slab, fobjs[0]);
+ offset = __VM_CACHELINE_ALIGN(offset);
+ count = (KMALLOC_SLAB_SIZE - offset) / (size + sizeof(void *));
+
+ /*
+ * However, the fobj[] array itself must be aligned, so we might
+ * have to reduce the count by 1. (We can do this becaues 'size'
+ * is already aligned as well).
+ */
+ offset = offsetof(struct kmalloc_slab, fobjs[count]);
+ offset = __VM_CACHELINE_ALIGN(offset);
+
+ if (offset + size * count > KMALLOC_SLAB_SIZE) {
+ --count;
+ offset = offsetof(struct kmalloc_slab, fobjs[count]);
+ offset = __VM_CACHELINE_ALIGN(offset);
+ KKASSERT (offset + size * count <= KMALLOC_SLAB_SIZE);
+ }
+
+ return count;
+}
+
void
malloc_mgt_init(struct malloc_type *type __unused,
struct kmalloc_mgt *mgt, size_t size)
{
size_t offset;
- size_t count;
+ size_t count, old_count;
bzero(mgt, sizeof(*mgt));
spin_init(&mgt->spin, "kmmgt");
@@ -291,7 +322,7 @@ malloc_mgt_init(struct malloc_type *type __unused,
* array by adding it to the object size.
*/
offset = offsetof(struct kmalloc_slab, fobjs[0]);
- offset = __VM_CACHELINE_ALIGN(offset);
+ kprintf("XXX malloc_mgt_init fobjs[0] offset %jx\n", (uintmax_t)offset);
count = (KMALLOC_SLAB_SIZE - offset) / (size + sizeof(void *));
/*
@@ -309,6 +340,13 @@ malloc_mgt_init(struct malloc_type *type __unused,
KKASSERT (offset + size * count <= KMALLOC_SLAB_SIZE);
}
+ old_count = malloc_mgt_old_count(size);
+ kprintf("XXX malloc_mgt_init count before %jx now %jx\n", old_count,
count);
+ if (old_count != count) {
+ kprintf("XXX malloc_mgt_init count changed! offset + size * count =
%jx\n",
+ (uintmax_t)(offset + size * count));
+ }
+
mgt->slab_offset = offset;
mgt->slab_count = count;
}
Output of dmesg|grep xxx; note all numbers are hex.
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 14d now 14d
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 14d now 14d
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 3c0 now 3c1
XXX malloc_mgt_init count changed! offset + size * count = 20000
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 3c0 now 3c1
XXX malloc_mgt_init count changed! offset + size * count = 20000
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 18e now 18e
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 18e now 18e
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 1ef now 1ef
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 1ef now 1ef
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 1ef now 1ef
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 1ef now 1ef
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 18e now 18e
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 18e now 18e
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 3c0 now 3c1
XXX malloc_mgt_init count changed! offset + size * count = 20000
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 3c0 now 3c1
XXX malloc_mgt_init count changed! offset + size * count = 20000
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 14d now 14d
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 14d now 14d
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 11e now 11e
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 11e now 11e
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 11e now 11e
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 11e now 11e
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 3c0 now 3c1
XXX malloc_mgt_init count changed! offset + size * count = 20000
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 3c0 now 3c1
XXX malloc_mgt_init count changed! offset + size * count = 20000
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 3c0 now 3c1
XXX malloc_mgt_init count changed! offset + size * count = 20000
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 3c0 now 3c1
XXX malloc_mgt_init count changed! offset + size * count = 20000
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before a8 now a8
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before a8 now a8
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before a8 now a8
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before a8 now a8
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before a8 now a8
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before a8 now a8
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before a8 now a8
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before a8 now a8
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before a8 now a8
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before a8 now a8
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before a8 now a8
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before a8 now a8
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 11e now 11e
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 11e now 11e
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 11e now 11e
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 11e now 11e
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 3c0 now 3c1
XXX malloc_mgt_init count changed! offset + size * count = 20000
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 3c0 now 3c1
XXX malloc_mgt_init count changed! offset + size * count = 20000
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 3c0 now 3c1
XXX malloc_mgt_init count changed! offset + size * count = 20000
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 3c0 now 3c1
XXX malloc_mgt_init count changed! offset + size * count = 20000
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before a8 now a8
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before a8 now a8
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before a8 now a8
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before a8 now a8
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before a8 now a8
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before a8 now a8
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before a8 now a8
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before a8 now a8
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before a8 now a8
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before a8 now a8
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before a8 now a8
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before a8 now a8
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 18e now 18e
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 18e now 18e
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 18e now 18e
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 18e now 18e
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 3c0 now 3c1
XXX malloc_mgt_init count changed! offset + size * count = 20000
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 3c0 now 3c1
XXX malloc_mgt_init count changed! offset + size * count = 20000
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 3c0 now 3c1
XXX malloc_mgt_init count changed! offset + size * count = 20000
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 3c0 now 3c1
XXX malloc_mgt_init count changed! offset + size * count = 20000
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 18e now 18e
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 18e now 18e
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 18e now 18e
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 18e now 18e
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 3c0 now 3c1
XXX malloc_mgt_init count changed! offset + size * count = 20000
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 3c0 now 3c1
XXX malloc_mgt_init count changed! offset + size * count = 20000
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 3c0 now 3c1
XXX malloc_mgt_init count changed! offset + size * count = 20000
XXX malloc_mgt_init fobjs[0] offset 160
XXX malloc_mgt_init count before 3c0 now 3c1
XXX malloc_mgt_init count changed! offset + size * count = 20000
--
James
