On 30.10.21 01:44, Boris Ostrovsky wrote:
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@lists.xenproject.org +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.
BP_EAGAIN should not stop waiting, as it might be intermediate in case some caches or buffers are freed.
Juergen