Messages in this thread | | | Date | Fri, 29 Oct 2021 19:44:31 -0400 | Subject | Re: [PATCH v3] xen/balloon: add late_initcall_sync() for initial ballooning done | From | Boris Ostrovsky <> |
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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.
-boris
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