1 files changed, 164 insertions, 44 deletions

diff --git a/migration/ram.c b/migration/ram.c
index 424df6d..2140785 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -48,7 +48,7 @@
 #include "qapi/qapi-commands-migration.h"
 #include "qapi/qmp/qerror.h"
 #include "trace.h"
-#include "exec/ram_addr.h"
+#include "system/ram_addr.h"
 #include "exec/target_page.h"
 #include "qemu/rcu_queue.h"
 #include "migration/colo.h"
@@ -91,6 +91,36 @@
 
 XBZRLECacheStats xbzrle_counters;
 
+/*
+ * This structure locates a specific location of a guest page.  In QEMU,
+ * it's described in a tuple of (ramblock, offset).
+ */
+struct PageLocation {
+    RAMBlock *block;
+    unsigned long offset;
+};
+typedef struct PageLocation PageLocation;
+
+/**
+ * PageLocationHint: describes a hint to a page location
+ *
+ * @valid     set if the hint is vaild and to be consumed
+ * @location: the hint content
+ *
+ * In postcopy preempt mode, the urgent channel may provide hints to the
+ * background channel, so that QEMU source can try to migrate whatever is
+ * right after the requested urgent pages.
+ *
+ * This is based on the assumption that the VM (already running on the
+ * destination side) tends to access the memory with spatial locality.
+ * This is also the default behavior of vanilla postcopy (preempt off).
+ */
+struct PageLocationHint {
+    bool valid;
+    PageLocation location;
+};
+typedef struct PageLocationHint PageLocationHint;
+
 /* used by the search for pages to send */
 struct PageSearchStatus {
     /* The migration channel used for a specific host page */
@@ -395,6 +425,13 @@ struct RAMState {
      * RAM migration.
      */
     unsigned int postcopy_bmap_sync_requested;
+    /*
+     * Page hint during postcopy when preempt mode is on.  Return path
+     * thread sets it, while background migration thread consumes it.
+     *
+     * Protected by @bitmap_mutex.
+     */
+    PageLocationHint page_hint;
 };
 typedef struct RAMState RAMState;
 
@@ -794,14 +831,22 @@ static inline bool migration_bitmap_clear_dirty(RAMState *rs,
     bool ret;
 
     /*
-     * Clear dirty bitmap if needed.  This _must_ be called before we
-     * send any of the page in the chunk because we need to make sure
-     * we can capture further page content changes when we sync dirty
-     * log the next time.  So as long as we are going to send any of
-     * the page in the chunk we clear the remote dirty bitmap for all.
-     * Clearing it earlier won't be a problem, but too late will.
+     * During the last stage (after source VM stopped), resetting the write
+     * protections isn't needed as we know there will be either (1) no
+     * further writes if migration will complete, or (2) migration fails
+     * at last then tracking isn't needed either.
      */
-    migration_clear_memory_region_dirty_bitmap(rb, page);
+    if (!rs->last_stage) {
+        /*
+         * Clear dirty bitmap if needed.  This _must_ be called before we
+         * send any of the page in the chunk because we need to make sure
+         * we can capture further page content changes when we sync dirty
+         * log the next time.  So as long as we are going to send any of
+         * the page in the chunk we clear the remote dirty bitmap for all.
+         * Clearing it earlier won't be a problem, but too late will.
+         */
+        migration_clear_memory_region_dirty_bitmap(rb, page);
+    }
 
     ret = test_and_clear_bit(page, rb->bmap);
     if (ret) {
@@ -811,8 +856,8 @@ static inline bool migration_bitmap_clear_dirty(RAMState *rs,
     return ret;
 }
 
-static void dirty_bitmap_clear_section(MemoryRegionSection *section,
-                                       void *opaque)
+static int dirty_bitmap_clear_section(MemoryRegionSection *section,
+                                      void *opaque)
 {
     const hwaddr offset = section->offset_within_region;
     const hwaddr size = int128_get64(section->size);
@@ -831,6 +876,7 @@ static void dirty_bitmap_clear_section(MemoryRegionSection *section,
     }
     *cleared_bits += bitmap_count_one_with_offset(rb->bmap, start, npages);
     bitmap_clear(rb->bmap, start, npages);
+    return 0;
 }
 
 /*
@@ -1144,32 +1190,6 @@ static int save_zero_page(RAMState *rs, PageSearchStatus *pss,
 }
 
 /*
- * @pages: the number of pages written by the control path,
- *        < 0 - error
- *        > 0 - number of pages written
- *
- * Return true if the pages has been saved, otherwise false is returned.
- */
-static bool control_save_page(PageSearchStatus *pss,
-                              ram_addr_t offset, int *pages)
-{
-    int ret;
-
-    ret = rdma_control_save_page(pss->pss_channel, pss->block->offset, offset,
-                                 TARGET_PAGE_SIZE);
-    if (ret == RAM_SAVE_CONTROL_NOT_SUPP) {
-        return false;
-    }
-
-    if (ret == RAM_SAVE_CONTROL_DELAYED) {
-        *pages = 1;
-        return true;
-    }
-    *pages = ret;
-    return true;
-}
-
-/*
  * directly send the page to the stream
  *
  * Returns the number of pages written.
@@ -1965,7 +1985,13 @@ static int ram_save_target_page(RAMState *rs, PageSearchStatus *pss)
     int res;
 
     /* Hand over to RDMA first */
-    if (control_save_page(pss, offset, &res)) {
+    if (migrate_rdma()) {
+        res = rdma_control_save_page(pss->pss_channel, pss->block->offset,
+                                     offset, TARGET_PAGE_SIZE);
+
+        if (res == RAM_SAVE_CONTROL_DELAYED) {
+            res = 1;
+        }
         return res;
     }
 
@@ -1976,9 +2002,8 @@ static int ram_save_target_page(RAMState *rs, PageSearchStatus *pss)
         }
     }
 
-    if (migrate_multifd()) {
-        RAMBlock *block = pss->block;
-        return ram_save_multifd_page(block, offset);
+    if (migrate_multifd() && !migration_in_postcopy()) {
+        return ram_save_multifd_page(pss->block, offset);
     }
 
     return ram_save_page(rs, pss);
@@ -2039,6 +2064,21 @@ static void pss_host_page_finish(PageSearchStatus *pss)
     pss->host_page_start = pss->host_page_end = 0;
 }
 
+static void ram_page_hint_update(RAMState *rs, PageSearchStatus *pss)
+{
+    PageLocationHint *hint = &rs->page_hint;
+
+    /* If there's a pending hint not consumed, don't bother */
+    if (hint->valid) {
+        return;
+    }
+
+    /* Provide a hint to the background stream otherwise */
+    hint->location.block = pss->block;
+    hint->location.offset = pss->page;
+    hint->valid = true;
+}
+
 /*
  * Send an urgent host page specified by `pss'.  Need to be called with
  * bitmap_mutex held.
@@ -2084,6 +2124,7 @@ out:
     /* For urgent requests, flush immediately if sent */
     if (sent) {
         qemu_fflush(pss->pss_channel);
+        ram_page_hint_update(rs, pss);
     }
     return ret;
 }
@@ -2171,6 +2212,30 @@ static int ram_save_host_page(RAMState *rs, PageSearchStatus *pss)
     return (res < 0 ? res : pages);
 }
 
+static bool ram_page_hint_valid(RAMState *rs)
+{
+    /* There's only page hint during postcopy preempt mode */
+    if (!postcopy_preempt_active()) {
+        return false;
+    }
+
+    return rs->page_hint.valid;
+}
+
+static void ram_page_hint_collect(RAMState *rs, RAMBlock **block,
+                                  unsigned long *page)
+{
+    PageLocationHint *hint = &rs->page_hint;
+
+    assert(hint->valid);
+
+    *block = hint->location.block;
+    *page = hint->location.offset;
+
+    /* Mark the hint consumed */
+    hint->valid = false;
+}
+
 /**
  * ram_find_and_save_block: finds a dirty page and sends it to f
  *
@@ -2187,6 +2252,8 @@ static int ram_save_host_page(RAMState *rs, PageSearchStatus *pss)
 static int ram_find_and_save_block(RAMState *rs)
 {
     PageSearchStatus *pss = &rs->pss[RAM_CHANNEL_PRECOPY];
+    unsigned long next_page;
+    RAMBlock *next_block;
     int pages = 0;
 
     /* No dirty page as there is zero RAM */
@@ -2206,7 +2273,14 @@ static int ram_find_and_save_block(RAMState *rs)
         rs->last_page = 0;
     }
 
-    pss_init(pss, rs->last_seen_block, rs->last_page);
+    if (ram_page_hint_valid(rs)) {
+        ram_page_hint_collect(rs, &next_block, &next_page);
+    } else {
+        next_block = rs->last_seen_block;
+        next_page = rs->last_page;
+    }
+
+    pss_init(pss, next_block, next_page);
 
     while (true){
         if (!get_queued_page(rs, pss)) {
@@ -2339,6 +2413,13 @@ static void ram_save_cleanup(void *opaque)
     ram_state_cleanup(rsp);
 }
 
+static void ram_page_hint_reset(PageLocationHint *hint)
+{
+    hint->location.block = NULL;
+    hint->location.offset = 0;
+    hint->valid = false;
+}
+
 static void ram_state_reset(RAMState *rs)
 {
     int i;
@@ -2351,6 +2432,8 @@ static void ram_state_reset(RAMState *rs)
     rs->last_page = 0;
     rs->last_version = ram_list.version;
     rs->xbzrle_started = false;
+
+    ram_page_hint_reset(&rs->page_hint);
 }
 
 #define MAX_WAIT 50 /* ms, half buffered_file limit */
@@ -3598,7 +3681,9 @@ static int ram_load_cleanup(void *opaque)
     RAMBlock *rb;
 
     RAMBLOCK_FOREACH_NOT_IGNORED(rb) {
-        qemu_ram_block_writeback(rb);
+        if (memory_region_is_nonvolatile(rb->mr)) {
+            qemu_ram_block_writeback(rb);
+        }
     }
 
     xbzrle_load_cleanup();
@@ -3963,8 +4048,6 @@ static void parse_ramblock_mapped_ram(QEMUFile *f, RAMBlock *block,
 
     /* Skip pages array */
     qemu_set_offset(f, block->pages_offset + length, SEEK_SET);
-
-    return;
 }
 
 static int parse_ramblock(QEMUFile *f, RAMBlock *block, ram_addr_t length)
@@ -4420,6 +4503,42 @@ static int ram_resume_prepare(MigrationState *s, void *opaque)
     return 0;
 }
 
+static bool ram_save_postcopy_prepare(QEMUFile *f, void *opaque, Error **errp)
+{
+    int ret;
+
+    if (migrate_multifd()) {
+        /*
+         * When multifd is enabled, source QEMU needs to make sure all the
+         * pages queued before postcopy starts have been flushed.
+         *
+         * The load of these pages must happen before switching to postcopy.
+         * It's because loading of guest pages (so far) in multifd recv
+         * threads is still non-atomic, so the load cannot happen with vCPUs
+         * running on the destination side.
+         *
+         * This flush and sync will guarantee that those pages are loaded
+         * _before_ postcopy starts on the destination. The rationale is,
+         * this happens before VM stops (and before source QEMU sends all
+         * the rest of the postcopy messages).  So when the destination QEMU
+         * receives the postcopy messages, it must have received the sync
+         * message on the main channel (either RAM_SAVE_FLAG_MULTIFD_FLUSH,
+         * or RAM_SAVE_FLAG_EOS), and such message would guarantee that
+         * all previous guest pages queued in the multifd channels are
+         * completely loaded.
+         */
+        ret = multifd_ram_flush_and_sync(f);
+        if (ret < 0) {
+            error_setg(errp, "%s: multifd flush and sync failed", __func__);
+            return false;
+        }
+    }
+
+    qemu_put_be64(f, RAM_SAVE_FLAG_EOS);
+
+    return true;
+}
+
 void postcopy_preempt_shutdown_file(MigrationState *s)
 {
     qemu_put_be64(s->postcopy_qemufile_src, RAM_SAVE_FLAG_EOS);
@@ -4439,6 +4558,7 @@ static SaveVMHandlers savevm_ram_handlers = {
     .load_setup = ram_load_setup,
     .load_cleanup = ram_load_cleanup,
     .resume_prepare = ram_resume_prepare,
+    .save_postcopy_prepare = ram_save_postcopy_prepare,
 };
 
 static void ram_mig_ram_block_resized(RAMBlockNotifier *n, void *host,