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Re: [PATCH v1 05/13] migrate/ram: Handle RAM block resizes during precop
From: |
David Hildenbrand |
Subject: |
Re: [PATCH v1 05/13] migrate/ram: Handle RAM block resizes during precopy |
Date: |
Thu, 20 Feb 2020 16:16:02 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 |
On 19.02.20 17:17, David Hildenbrand wrote:
> Resizing while migrating is dangerous and does not work as expected.
> The whole migration code works on the usable_length of ram blocks and does
> not expect this to change at random points in time.
>
> In the case of precopy, the ram block size must not change on the source,
> after syncing the RAM block list in ram_save_setup(), so as long as the
> guest is still running on the source.
>
> Resizing can be trigger *after* (but not during) a reset in
> ACPI code by the guest
> - hw/arm/virt-acpi-build.c:acpi_ram_update()
> - hw/i386/acpi-build.c:acpi_ram_update()
>
> Use the ram block notifier to get notified about resizes. Let's simply
> cancel migration and indicate the reason. We'll continue running on the
> source. No harm done.
>
> Update the documentation. Postcopy will be handled separately.
>
> Cc: "Dr. David Alan Gilbert" <address@hidden>
> Cc: Juan Quintela <address@hidden>
> Cc: Eduardo Habkost <address@hidden>
> Cc: Paolo Bonzini <address@hidden>
> Cc: Igor Mammedov <address@hidden>
> Cc: "Michael S. Tsirkin" <address@hidden>
> Cc: Richard Henderson <address@hidden>
> Cc: Shannon Zhao <address@hidden>
> Cc: Alex Bennée <address@hidden>
> Cc: Peter Xu <address@hidden>
> Signed-off-by: David Hildenbrand <address@hidden>
> ---
> exec.c | 5 +++--
> include/exec/memory.h | 10 ++++++----
> migration/migration.c | 9 +++++++--
> migration/migration.h | 1 +
> migration/ram.c | 41 +++++++++++++++++++++++++++++++++++++++++
> 5 files changed, 58 insertions(+), 8 deletions(-)
>
> diff --git a/exec.c b/exec.c
> index b75250e773..8b015821d6 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -2120,8 +2120,9 @@ static int memory_try_enable_merging(void *addr, size_t
> len)
> return qemu_madvise(addr, len, QEMU_MADV_MERGEABLE);
> }
>
> -/* Only legal before guest might have detected the memory size: e.g. on
> - * incoming migration, or right after reset.
> +/*
> + * Resizing RAM while migrating can result in the migration being canceled.
> + * Care has to be taken if the guest might have already detected the memory.
> *
> * As memory core doesn't know how is memory accessed, it is up to
> * resize callback to update device state and/or add assertions to detect
> diff --git a/include/exec/memory.h b/include/exec/memory.h
> index e85b7de99a..de111347e8 100644
> --- a/include/exec/memory.h
> +++ b/include/exec/memory.h
> @@ -113,7 +113,7 @@ typedef struct IOMMUNotifier IOMMUNotifier;
> #define RAM_SHARED (1 << 1)
>
> /* Only a portion of RAM (used_length) is actually used, and migrated.
> - * This used_length size can change across reboots.
> + * Resizing RAM while migrating can result in the migration being canceled.
> */
> #define RAM_RESIZEABLE (1 << 2)
>
> @@ -843,7 +843,9 @@ void memory_region_init_ram_shared_nomigrate(MemoryRegion
> *mr,
> * RAM. Accesses into the region will
> * modify memory directly. Only an
> initial
> * portion of this RAM is actually used.
> - * The used size can change across
> reboots.
> + * Changing the size while migrating
> + * can result in the migration being
> + * canceled.
> *
> * @mr: the #MemoryRegion to be initialized.
> * @owner: the object that tracks the region's reference count
> @@ -1464,8 +1466,8 @@ void *memory_region_get_ram_ptr(MemoryRegion *mr);
>
> /* memory_region_ram_resize: Resize a RAM region.
> *
> - * Only legal before guest might have detected the memory size: e.g. on
> - * incoming migration, or right after reset.
> + * Resizing RAM while migrating can result in the migration being canceled.
> + * Care has to be taken if the guest might have already detected the memory.
> *
> * @mr: a memory region created with @memory_region_init_resizeable_ram.
> * @newsize: the new size the region
> diff --git a/migration/migration.c b/migration/migration.c
> index 8fb68795dc..ac9751dbe5 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -175,13 +175,18 @@ void migration_object_init(void)
> }
> }
>
> +void migration_cancel(void)
> +{
> + migrate_fd_cancel(current_migration);
> +}
> +
> void migration_shutdown(void)
> {
> /*
> * Cancel the current migration - that will (eventually)
> * stop the migration using this structure
> */
> - migrate_fd_cancel(current_migration);
> + migration_cancel();
> object_unref(OBJECT(current_migration));
> }
>
> @@ -2019,7 +2024,7 @@ void qmp_migrate(const char *uri, bool has_blk, bool
> blk,
>
> void qmp_migrate_cancel(Error **errp)
> {
> - migrate_fd_cancel(migrate_get_current());
> + migration_cancel();
> }
>
> void qmp_migrate_continue(MigrationStatus state, Error **errp)
> diff --git a/migration/migration.h b/migration/migration.h
> index 8473ddfc88..79fd74afa5 100644
> --- a/migration/migration.h
> +++ b/migration/migration.h
> @@ -343,5 +343,6 @@ int foreach_not_ignored_block(RAMBlockIterFunc func, void
> *opaque);
> void migration_make_urgent_request(void);
> void migration_consume_urgent_request(void);
> bool migration_rate_limit(void);
> +void migration_cancel(void);
>
> #endif
> diff --git a/migration/ram.c b/migration/ram.c
> index ed23ed1c7c..57f32011a3 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 +3711,48 @@ 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)
> +{
> + ram_addr_t offset;
> + Error *err = NULL;
> + RAMBlock *rb = qemu_ram_block_from_host(host, false, &offset);
> +
> + if (ramblock_is_ignored(rb)) {
> + return;
> + }
> +
> + /*
> + * Some resizes are triggered on the migration target by precopy code,
> + * when synchronizing RAM block sizes. In these cases, the VM is not
> + * running and migration is not idle. We have to ignore these resizes,
> + * as we only care about resizes during precopy on the migration source.
> + * This handler is always registered, so ignore when migration is idle.
> + */
> + if (migration_is_idle() || !runstate_is_running() ||
> + postcopy_is_running()) {
> + return;
> + }
> +
> + /*
> + * 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 block '%s' resized during precopy.", rb->idstr);
> + migrate_set_error(migrate_get_current(), err);
> + error_free(err);
> + migration_cancel();
> +}
> +
> +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);
> }
>
So, this seems to work very reliably when triggering a resize of a RAM
block during system reset (using my virtio-mem prototype):
(qemu) info migrate
globals:
store-global-state: on
only-migratable: off
send-configuration: on
send-section-footer: on
decompress-error-check: on
clear-bitmap-shift: 18
Migration status: cancelled
total time: 0 milliseconds
And from QEMU
qemu-system-x86_64: RAM block '0000:00:03.0/mem1' resized during precopy.
--
Thanks,
David / dhildenb
- Re: [PATCH v1 02/13] stubs/ram-block: Remove stubs that are no longer needed, (continued)
- [PATCH v1 05/13] migrate/ram: Handle RAM block resizes during precopy, David Hildenbrand, 2020/02/19
- Re: [PATCH v1 05/13] migrate/ram: Handle RAM block resizes during precopy,
David Hildenbrand <=
- Re: [PATCH v1 05/13] migrate/ram: Handle RAM block resizes during precopy, Peter Xu, 2020/02/20
- Re: [PATCH v1 05/13] migrate/ram: Handle RAM block resizes during precopy, David Hildenbrand, 2020/02/21
- Re: [PATCH v1 05/13] migrate/ram: Handle RAM block resizes during precopy, David Hildenbrand, 2020/02/21
- Re: [PATCH v1 05/13] migrate/ram: Handle RAM block resizes during precopy, David Hildenbrand, 2020/02/21
- Re: [PATCH v1 05/13] migrate/ram: Handle RAM block resizes during precopy, Peter Xu, 2020/02/21
Re: [PATCH v1 05/13] migrate/ram: Handle RAM block resizes during precopy, Dr. David Alan Gilbert, 2020/02/21
[PATCH v1 08/13] migrate/ram: Simplify host page handling in ram_load_postcopy(), David Hildenbrand, 2020/02/19