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Re: [PATCH RFC] memory: Don't allow to resize RAM while migrating
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [PATCH RFC] memory: Don't allow to resize RAM while migrating |
Date: |
Fri, 14 Feb 2020 15:14:50 +0000 |
User-agent: |
Mutt/1.13.3 (2020-01-12) |
* David Hildenbrand (address@hidden) wrote:
>
> >> diff --git a/migration/ram.c b/migration/ram.c
> >> index ed23ed1c7c..f86f32b453 100644
> >> --- a/migration/ram.c
> >> +++ b/migration/ram.c
> >> @@ -52,6 +52,7 @@
> >> #include "migration/colo.h"
> >> #include "block.h"
> >> #include "sysemu/sysemu.h"
> >> +#include "sysemu/runstate.h"
> >> #include "savevm.h"
> >> #include "qemu/iov.h"
> >> #include "multifd.h"
> >> @@ -3710,8 +3711,49 @@ static SaveVMHandlers savevm_ram_handlers = {
> >> .resume_prepare = ram_resume_prepare,
> >> };
> >>
> >> +static void ram_mig_ram_block_resized(RAMBlockNotifier *n, void *host,
> >> + size_t old_size, size_t new_size)
> >> +{
> >> + /*
> >> + * We don't care about resizes triggered on incoming migration (when
> >> + * syncing ram blocks), or of course, when no migration is going on.
> >> + */
> >> + if (migration_is_idle() || !runstate_is_running()) {
> >> + return;
> >> + }
> >> +
> >> + if (!postcopy_is_running()) {
> >> + Error *err = NULL;
> >> +
> >> + /*
> >> + * Precopy code cannot deal with the size of ram blocks changing
> >> at
> >> + * random points in time. We're still running on the source, abort
> >> + * the migration and continue running here. Make sure to wait
> >> until
> >> + * migration was canceled.
> >> + */
> >> + error_setg(&err, "RAM resized during precopy.");
> >> + migrate_set_error(migrate_get_current(), err);
> >> + error_free(err);
> >> + migration_cancel();
> >
> > If we can't do anything else, this is reasonable.
> >
> > But as discussed before, it is still not fully clear to me _why_ are
> > ramblocks changing if we have disabled add/remove memory during migration.
>
>
> Ramblock add/remove is ties to device add/remove, which we block.
>
> Resize, however, it not. Here, the resize happens while the guest is
> booting up. The content/size of the ram block depends also on previous
> guest action AFAIK. There is no way from stopping the guest from doing
> that. It's required for the guest to continue booting (with ACPI).
>
> I'm currently working on a project which reuses resizable ram blocks in
> different context. There, I can simply defer/avoid resizing when
> migration is active. In the ACPI case, however, we cannot avoid it.
>
> Hope that answers your question
>
> >
> >> + } else {
> >> + /*
> >> + * Postcopy code cannot deal with the size of ram blocks changing
> >> at
> >> + * random points in time. We're running on the target. Fail hard.
> >> + *
> >> + * TODO: How to handle this in a better way?
> >> + */
> >> + error_report("RAM resized during postcopy.");
> >> + exit(-1);
> >
> > Idea is good, but we also need to exit destination, not only source, no?
>
> @Dave, any idea what could be the right thing to do here?
I think that's OK; postcopy_is_running() will return true on the
destination (e.g. see it's use in ram_load()) and should work.
I'd really appreciate if you could print hte RAMBlock or something at
this point - when we hit this error we're going to want to try and
figure out why.
Dave
> >
> >> + }
> >> +}
> >
> >
> >
> >> +static RAMBlockNotifier ram_mig_ram_notifier = {
> >> + .ram_block_resized = ram_mig_ram_block_resized,
> >> +};
> >> +
> >> void ram_mig_init(void)
> >> {
> >> qemu_mutex_init(&XBZRLE.lock);
> >> register_savevm_live("ram", 0, 4, &savevm_ram_handlers, &ram_state);
> >> + ram_block_notifier_add(&ram_mig_ram_notifier);
> >> }
> >
> > Shouldn't we remove the notifier when we finish the migration.
>
> It's called from main() unconditionally (so not when migration starts),
> so the notifier remains active the whole QEMU lifetime (which should be
> fine AFAIKT).
>
> --
> Thanks,
>
> David / dhildenb
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK
- Re: [PATCH RFC] memory: Don't allow to resize RAM while migrating, (continued)
- Re: [PATCH RFC] memory: Don't allow to resize RAM while migrating, Dr. David Alan Gilbert, 2020/02/14
- Re: [PATCH RFC] memory: Don't allow to resize RAM while migrating, David Hildenbrand, 2020/02/14
- Re: [PATCH RFC] memory: Don't allow to resize RAM while migrating, Dr. David Alan Gilbert, 2020/02/14
- Re: [PATCH RFC] memory: Don't allow to resize RAM while migrating, David Hildenbrand, 2020/02/14
- Re: [PATCH RFC] memory: Don't allow to resize RAM while migrating, Dr. David Alan Gilbert, 2020/02/14
- Re: [PATCH RFC] memory: Don't allow to resize RAM while migrating, David Hildenbrand, 2020/02/14
- Re: [PATCH RFC] memory: Don't allow to resize RAM while migrating, David Hildenbrand, 2020/02/14
- Re: [PATCH RFC] memory: Don't allow to resize RAM while migrating, Juan Quintela, 2020/02/14
- Re: [PATCH RFC] memory: Don't allow to resize RAM while migrating, David Hildenbrand, 2020/02/14
- Re: [PATCH RFC] memory: Don't allow to resize RAM while migrating,
Dr. David Alan Gilbert <=
- Re: [PATCH RFC] memory: Don't allow to resize RAM while migrating, Peter Xu, 2020/02/14
- Re: [PATCH RFC] memory: Don't allow to resize RAM while migrating, David Hildenbrand, 2020/02/14
- Re: [PATCH RFC] memory: Don't allow to resize RAM while migrating, Peter Xu, 2020/02/14
- Re: [PATCH RFC] memory: Don't allow to resize RAM while migrating, David Hildenbrand, 2020/02/14
- Re: [PATCH RFC] memory: Don't allow to resize RAM while migrating, Peter Xu, 2020/02/14
- Re: [PATCH RFC] memory: Don't allow to resize RAM while migrating, David Hildenbrand, 2020/02/14
- Re: [PATCH RFC] memory: Don't allow to resize RAM while migrating, Peter Xu, 2020/02/14