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Re: [PATCH v3] xen/balloon: add late_initcall_sync() for initial ballooning done
- To: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
- From: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
- Date: Fri, 29 Oct 2021 19:44:31 -0400
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- Cc: Juergen Gross <jgross@xxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, Stefano Stabellini <sstabellini@xxxxxxxxxx>, stable@xxxxxxxxxxxxxxx
- Delivery-date: Fri, 29 Oct 2021 23:45:20 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 10/29/21 6:18 PM, Marek Marczykowski-Górecki wrote:
On Fri, Oct 29, 2021 at 05:46:18PM -0400, Boris Ostrovsky wrote:
On 10/29/21 10:20 AM, Juergen Gross wrote:
--- a/Documentation/ABI/stable/sysfs-devices-system-xen_memory
+++ b/Documentation/ABI/stable/sysfs-devices-system-xen_memory
@@ -84,3 +84,13 @@ Description:
Control scrubbing pages before returning them to Xen for others
domains
use. Can be set with xen_scrub_pages cmdline
parameter. Default value controlled with
CONFIG_XEN_SCRUB_PAGES_DEFAULT.
+
+What: /sys/devices/system/xen_memory/xen_memory0/boot_timeout
+Date: November 2021
+KernelVersion: 5.16
+Contact: xen-devel@xxxxxxxxxxxxxxxxxxxx
+Description:
+ The time (in seconds) to wait before giving up to boot in case
+ initial ballooning fails to free enough memory. Applies only
+ when running as HVM or PVH guest and started with less memory
+ configured than allowed at max.
How is this going to be used? We only need this during boot.
- state = update_schedule(state);
+ balloon_state = update_schedule(balloon_state);
Now that balloon_state has whole file scope it can probably be updated inside
update_schedule().
+ while ((credit = current_credit()) < 0) {
+ if (credit != last_credit) {
+ last_changed = jiffies;
+ last_credit = credit;
+ }
+ if (balloon_state == BP_ECANCELED) {
What about other states? We are really waiting for BP_DONE, aren't we?
BP_DONE is set also as an intermediate step:
balloon_state = decrease_reservation(n_pages,
GFP_BALLOON);
if (balloon_state == BP_DONE && n_pages != -credit &&
n_pages < totalreserve_pages)
balloon_state = BP_EAGAIN;
It would be bad to finish waiting in this case.
RIght, but if we were to say 'if (balloon_state != BP_DONE)' the worst that can
happen is that we will continue on to the next iteration without warning and/or
panicing. Of course, there is a chance thaton the next iteration the same thing
will happen but I think chances of hitting this race every time are infinitely
low. We can also check for current_credit() again.
The question is whether we do want to continue waiting if we are in BP_AGAIN. I
don't think BP_WAIT is possible in this case although this may change in the
future and we will forget to update this code.
-boris
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