On Tue, Sep 15, 2020 at 10:22:09AM -0400, Mark Johnston wrote:
> On Tue, Sep 15, 2020 at 05:15:30PM +0300, Konstantin Belousov wrote:
> > On Sat, Aug 29, 2020 at 04:29:53AM +0000, Warner Losh wrote:
> > > Author: imp
> > > Date: Sat Aug 29 04:29:53 2020
> > > New Revision: 364944
> > > URL: https://svnweb.freebsd.org/changeset/base/364944
> > >
> > > Log:
> > > devctl: move to using a uma zone
> > >
> > > Convert the memory management of devctl. Rewrite if to make better
> > > use of memory. This eliminates several mallocs (5? worse case) needed
> > > to send a message. It's now possible to always send a message, though
> > > if things are really backed up the oldest message will be dropped to
> > > free up space for the newest.
> > >
> > > Add a static bus_child_{location,pnpinfo}_sb to start migrating to
> > > sbuf instead of buffer + length. Use it in the new code. Other code
> > > will be converted later (bus_child_*_str is only used inside of
> > > subr_bus.c, though implemented in ~100 places in the tree).
> > >
> > > Reviewed by: markj@
> > > Differential Revision: https://reviews.freebsd.org/D26140
> > >
> > > Modified:
> > > head/sys/kern/subr_bus.c
> > >
> >
> > > + } else {
> > > + /* dei can't be NULL -- we know we have at least one in the
> > > zone */
> > > + dei = uma_zalloc(devsoftc.zone, M_NOWAIT);
> > > + MPASS(dei != NULL);
> > This does not work. I believe you need to disable per-cpu cache for the
> > zone, at least. But I am not sure it is enough.
>
> From the report we have:
>
> db:0:pho> show uma
> Zone Size Used Free Requests Sleeps Bucket Total
> Mem XFree
> DEVCTL 1024 6415164 0 6416203 0 16
> 6569127936 0
>
> so it looks like the primary problem is a leak.
>
> > https://people.freebsd.org/~pho/stress/log/kostik1314.txt
devctl_queue() does not maintain the queue length bound, so if devd goes
away (due to an OOM kill in this case), we can end up with a large
backlog. This hack might be sufficient.
diff --git a/sys/kern/subr_bus.c b/sys/kern/subr_bus.c
index 19c056ab9974..91c57cdfae5b 100644
--- a/sys/kern/subr_bus.c
+++ b/sys/kern/subr_bus.c
@@ -635,7 +635,14 @@ devctl_queue(struct dev_event_info *dei)
{
mtx_lock(&devsoftc.mtx);
STAILQ_INSERT_TAIL(&devsoftc.devq, dei, dei_link);
- devsoftc.queued++;
+ if (devctl_queue_length != 0 &&
+ devctl_queue_length == devsoftc.queued) {
+ dei = STAILQ_FIRST(&devsoftc.devq);
+ STAILQ_REMOVE_HEAD(&devsoftc.devq, dei_link);
+ uma_zfree(devsoftc.zone, dei);
+ } else {
+ devsoftc.queued++;
+ }
cv_broadcast(&devsoftc.cv);
KNOTE_LOCKED(&devsoftc.sel.si_note, 0);
mtx_unlock(&devsoftc.mtx);
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