migration: Maintain postcopy faulted addresses

Maintain a list of faulted addresses on the destination host for which we're
waiting on.  This is implemented using a GTree rather than a real list to make
sure even there're plenty of vCPUs/threads that are faulting, the lookup will
still be fast with O(log(N)) (because we'll do that after placing each page).
It should bring a slight overhead, but ideally that shouldn't be a big problem
simply because in most cases the requested page list will be short.

Actually we did similar things for postcopy blocktime measurements.  This patch
didn't use that simply because:

  (1) blocktime measurement is towards vcpu threads only, but here we need to
      record all faulted addresses, including main thread and external
      thread (like, DPDK via vhost-user).

  (2) blocktime measurement will require UFFD_FEATURE_THREAD_ID, but here we
      don't want to add that extra dependency on the kernel version since not
      necessary.  E.g., we don't need to know which thread faulted on which
      page, we also don't care about multiple threads faulting on the same
      page.  But we only care about what addresses are faulted so waiting for a
      page copying from src.

  (3) blocktime measurement is not enabled by default.  However we need this by
      default especially for postcopy recover.

Another thing to mention is that this patch introduced a new mutex to serialize
the receivedmap and the page_requested tree, however that serialization does
not cover other procedures like UFFDIO_COPY.

Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20201021212721.440373-4-peterx@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

1 files changed, 18 insertions, 1 deletions

diff --git a/migration/migration.h b/migration/migration.h
index 9c1cba9..d096b77 100644
--- a/migration/migration.h
+++ b/migration/migration.h
@@ -104,6 +104,23 @@ struct MigrationIncomingState {
 
     /* List of listening socket addresses  */
     SocketAddressList *socket_address_list;
+
+    /* A tree of pages that we requested to the source VM */
+    GTree *page_requested;
+    /* For debugging purpose only, but would be nice to keep */
+    int page_requested_count;
+    /*
+     * The mutex helps to maintain the requested pages that we sent to the
+     * source, IOW, to guarantee coherent between the page_requests tree and
+     * the per-ramblock receivedmap.  Note! This does not guarantee consistency
+     * of the real page copy procedures (using UFFDIO_[ZERO]COPY).  E.g., even
+     * if one bit in receivedmap is cleared, UFFDIO_COPY could have happened
+     * for that page already.  This is intended so that the mutex won't
+     * serialize and blocked by slow operations like UFFDIO_* ioctls.  However
+     * this should be enough to make sure the page_requested tree always
+     * contains valid information.
+     */
+    QemuMutex page_request_mutex;
 };
 
 MigrationIncomingState *migration_incoming_get_current(void);
@@ -331,7 +348,7 @@ void migrate_send_rp_shut(MigrationIncomingState *mis,
 void migrate_send_rp_pong(MigrationIncomingState *mis,
                           uint32_t value);
 int migrate_send_rp_req_pages(MigrationIncomingState *mis, RAMBlock *rb,
-                              ram_addr_t start);
+                              ram_addr_t start, uint64_t haddr);
 int migrate_send_rp_message_req_pages(MigrationIncomingState *mis,
                                       RAMBlock *rb, ram_addr_t start);
 void migrate_send_rp_recv_bitmap(MigrationIncomingState *mis,