On 22/09/25(Mon) 09:24, Miod Vallat wrote:
> > Interesting. Could you enter ddb and report a trace of the ssh client
> > stuck on "pmrwait"? At the same time, could you get "ps", "show uvm",
> > "show all pools" and "show bcstats"?
>
> I have rebooted the machine since, but I'll do it next time.
>
> > Do I understand correctly that the #ifdef __sh__ doesn't make a
> > difference for your machine?
>
> Yes.
>
> > Indeed, that said is the pdaemon currently running? `pdwoke' is quite
> > high. So the question is does the ssh client keeps hitting the memory
> > limit? Or is it stuck there?
>
> As I said, its cpu time is slowly increasing. But it did not appear to
> make any significant progress after 8 hours...
Diff below includes a fix for a missing wakeup. It might correspond to
the bug you're seeing.
Problem is that there are two sleep channels and two mechanism for OOM
situations. The IOdone daemon was waking only one of the two.
Does it help?
Index: uvm/uvm_pdaemon.c
===================================================================
RCS file: /cvs/src/sys/uvm/uvm_pdaemon.c,v
diff -u -p -r1.137 uvm_pdaemon.c
--- uvm/uvm_pdaemon.c 2 Jun 2025 18:49:04 -0000 1.137
+++ uvm/uvm_pdaemon.c 24 Sep 2025 10:11:11 -0000
@@ -303,10 +303,10 @@ uvm_pageout(void *arg)
* wake up any waiters.
*/
uvm_lock_fpageq();
- if (uvmexp.free > uvmexp.reserve_kernel || uvmexp.paging == 0) {
- wakeup(&uvmexp.free);
- }
-
+ /*
+ * Wake waiter on pma first because they are more likely
+ * to starve on low pages.
+ */
if (pma != NULL) {
/*
* XXX If UVM_PMA_FREED isn't set, no pages
@@ -320,8 +320,11 @@ uvm_pageout(void *arg)
wakeup(pma);
}
}
+ if (uvmexp.free > uvmexp.reserve_kernel || uvmexp.paging == 0)
+ wakeup(&uvmexp.free);
uvm_unlock_fpageq();
+
/*
* scan done. unlock page queues (the only lock we are holding)
*/
@@ -377,8 +380,11 @@ uvm_aiodone_daemon(void *arg)
uvm_lock_fpageq();
atomic_sub_int(&uvmexp.paging, npages);
- wakeup(uvmexp.free <= uvmexp.reserve_kernel ? &uvm.pagedaemon :
- &uvmexp.free);
+ if (uvmexp.free <= uvmexp.reserve_kernel ||
+ !TAILQ_EMPTY(&uvm.pmr_control.allocs))
+ wakeup(&uvm.pagedaemon);
+ else
+ wakeup(&uvmexp.free);
uvm_unlock_fpageq();
}
}
