Hello, a developer here at work asked me to go over
some of the swapper code with him.
We came across something we both couldn't understand,
so I was wondering if anyone had looked at this.
in dev/md/md.c mdstart_swap() there is the following code,
it seems that in the case of VM_PAGER_ERROR most of the state
is unwound, however the page is not freed. Is this a bug or
are we missing something? How is the page released?
rv = VM_PAGER_OK;
VM_OBJECT_LOCK(sc->object);
vm_object_pip_add(sc->object, 1);
for (i = bp->bio_offset / PAGE_SIZE; i <= lastp; i++) {
len = ((i == lastp) ? lastend : PAGE_SIZE) - offs;
m = vm_page_grab(sc->object, i,
VM_ALLOC_NORMAL|VM_ALLOC_RETRY);
VM_OBJECT_UNLOCK(sc->object);
sched_pin();
sf = sf_buf_alloc(m, SFB_CPUPRIVATE);
VM_OBJECT_LOCK(sc->object);
if (bp->bio_cmd == BIO_READ) {
if (m->valid != VM_PAGE_BITS_ALL)
rv = vm_pager_get_pages(sc->object, &m, 1, 0);
if (rv == VM_PAGER_ERROR) {
sf_buf_free(sf);
sched_unpin();
vm_page_lock_queues();
vm_page_wakeup(m);
vm_page_unlock_queues();
break;
}
bcopy((void *)(sf_buf_kva(sf) + offs), p, len); } else if (bp->bio_cmd == BIO_WRITE) {
if (len != PAGE_SIZE && m->valid != VM_PAGE_BITS_ALL)
rv = vm_pager_get_pages(sc->object, &m, 1, 0);
if (rv == VM_PAGER_ERROR) {
sf_buf_free(sf);
sched_unpin();
vm_page_lock_queues();
vm_page_wakeup(m);
vm_page_unlock_queues();
break;
}
--
- Alfred Perlstein