On 13/10/14 09:32, Rusty Russell wrote:
"Denis V. Lunev" <d...@parallels.com> writes:
From: Raushaniya Maksudova <rmaksud...@parallels.com>

Excessive virtio_balloon inflation can cause invocation of OOM-killer,
when Linux is under severe memory pressure. Various mechanisms are
responsible for correct virtio_balloon memory management. Nevertheless
it is often the case that these control tools does not have enough time
to react on fast changing memory load. As a result OS runs out of memory
and invokes OOM-killer. The balancing of memory by use of the virtio
balloon should not cause the termination of processes while there are
pages in the balloon. Now there is no way for virtio balloon driver to
free some memory at the last moment before some process will be get
killed by OOM-killer.
This makes some amount of sense.

But I suggest a few minor changes:

+static int oom_vballoon_pages = OOM_VBALLOON_DEFAULT_PAGES;
+module_param(oom_vballoon_pages, int, S_IRUSR | S_IWUSR);
+MODULE_PARM_DESC(oom_vballoon_pages, "pages to free on OOM");
Since this is already prefixed with "virtio_balloon." I suggest just
calling it "oom_pages".
ok, will do

+static int virtballoon_oom_notify(struct notifier_block *self,
+                                 unsigned long dummy, void *parm)
+       unsigned int num_freed_pages;
+       unsigned long *freed = (unsigned long *)parm;
+       struct virtio_balloon *vb = container_of((struct notifier_block *)self,
+                                                struct virtio_balloon, nb);
Why cast self here?
this is a piece from a previous version of the patch, I'll fix this and resend.

+       num_freed_pages = leak_balloon(vb, oom_vballoon_pages);
+       update_balloon_size(vb);
+       *freed += num_freed_pages;
+       return NOTIFY_OK;

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