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Subject: Re: [virtio-dev] Re: [PATCH v10 6/7] migration/ram.c: add a function to disable the bulk stage
On 12/03/2018 04:20 PM, Wei Wang wrote:
On 12/03/2018 01:31 PM, Peter Xu wrote:On Mon, Dec 03, 2018 at 10:18:30AM +0800, Wei Wang wrote:This patch adds a function to enable a precopy notifier callback outside the migration subsystem to disable the bulk stage flag. This is needed bythe free page optimization offered by virtio-balloon. Signed-off-by: Wei Wang <wei.w.wang@intel.com> CC: Dr. David Alan Gilbert <dgilbert@redhat.com> CC: Juan Quintela <quintela@redhat.com> CC: Michael S. Tsirkin <mst@redhat.com> CC: Peter Xu <peterx@redhat.com> --- include/migration/misc.h | 1 + migration/ram.c | 9 +++++++++ 2 files changed, 10 insertions(+) diff --git a/include/migration/misc.h b/include/migration/misc.h index 15f8d00..47e7ff5 100644 --- a/include/migration/misc.h +++ b/include/migration/misc.h @@ -37,6 +37,7 @@ void precopy_infrastructure_init(void); void precopy_add_notifier(NotifierWithReturn *n); void precopy_remove_notifier(NotifierWithReturn *n); int precopy_notify(PrecopyNotifyReason reason, Error **errp); +void precopy_disable_bulk_stage(void); void ram_mig_init(void); void qemu_guest_free_page_hint(void *addr, size_t len); diff --git a/migration/ram.c b/migration/ram.c index b90a3f2..739dc97 100644 --- a/migration/ram.c +++ b/migration/ram.c@@ -354,6 +354,15 @@ int precopy_notify(PrecopyNotifyReason reason, Error **errp) return notifier_with_return_list_notify(&precopy_notifier_list, &pnd);} +void precopy_disable_bulk_stage(void) +{ + if (!ram_state) { + return; + } + + ram_state->ram_bulk_stage = false; +} +This one is a bit tricky. E.g., I think it'll at least affect XBZRLE and compression somehow. Since we will have the on-off switch for balloon free page hinting so the user can at least decide what features to use, with that I don't see much issue with it so far. But I'd also like to see how other people see this change.Yes. I think it would be better that this optimization could co-exist with thecompression feature. How about adding a new flag "ram_state->free_page_optimization_enabled"? We will then need a change in migration_bitmap_find_dirty: - if (rs->ram_bulk_stage && start > 0) {+ if (!rs->free_page_optimization_enabled && rs->ram_bulk_stage && start > 0) {next = start + 1; } else { next = find_next_bit(bitmap, size, start); }
Btw, with the new flag, this patch is not needed, so "ram_bulk_stage" will not be changed.
Best, Wei
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