migration: do not sent zero pages in bulk stage

during bulk stage of ram migration if a page is a
zero page do not send it at all.
the memory at the destination reads as zero anyway.

even if there is an madvise with QEMU_MADV_DONTNEED
at the target upon receipt of a zero page I have observed
that the target starts swapping if the memory is overcommitted.
it seems that the pages are dropped asynchronously.

this patch also updates QMP to return the number of
skipped pages in MigrationStats.

Signed-off-by: Peter Lieven <pl@kamp.de>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

diff --git a/arch_init.c b/arch_init.c
index 1291bd2b3a009b3cb4206efb00d86cc229f8af3b..3a0d02eafac7e6ae02dcf617e5f7e3661c3da1d9 100644 (file)
--- a/arch_init.c
+++ b/arch_init.c
@@ -183,6 +183,7 @@ int64_t xbzrle_cache_resize(int64_t new_size)
 /* accounting for migration statistics */
 typedef struct AccountingInfo {
     uint64_t dup_pages;
+    uint64_t skipped_pages;
     uint64_t norm_pages;
     uint64_t iterations;
     uint64_t xbzrle_bytes;
@@ -208,6 +209,16 @@ uint64_t dup_mig_pages_transferred(void)
     return acct_info.dup_pages;
 }
 
+uint64_t skipped_mig_bytes_transferred(void)
+{
+    return acct_info.skipped_pages * TARGET_PAGE_SIZE;
+}
+
+uint64_t skipped_mig_pages_transferred(void)
+{
+    return acct_info.skipped_pages;
+}
+
 uint64_t norm_mig_bytes_transferred(void)
 {
     return acct_info.norm_pages * TARGET_PAGE_SIZE;
@@ -440,10 +451,15 @@ static int ram_save_block(QEMUFile *f, bool last_stage)
             bytes_sent = -1;
             if (is_zero_page(p)) {
                 acct_info.dup_pages++;
-                bytes_sent = save_block_hdr(f, block, offset, cont,
-                                            RAM_SAVE_FLAG_COMPRESS);
-                qemu_put_byte(f, 0);
-                bytes_sent++;
+                if (!ram_bulk_stage) {
+                    bytes_sent = save_block_hdr(f, block, offset, cont,
+                                                RAM_SAVE_FLAG_COMPRESS);
+                    qemu_put_byte(f, 0);
+                    bytes_sent++;
+                } else {
+                    acct_info.skipped_pages++;
+                    bytes_sent = 0;
+                }
             } else if (migrate_use_xbzrle()) {
                 current_addr = block->offset + offset;
                 bytes_sent = save_xbzrle_page(f, p, current_addr, block,

diff --git a/hmp.c b/hmp.c
index b0a861cfbb0eba7c93b8698a1a53da30cd73b9ff..e3e833edf4744e0efb01e2d87821d3e1cf14ae0c 100644 (file)
--- a/hmp.c
+++ b/hmp.c
@@ -173,6 +173,8 @@ void hmp_info_migrate(Monitor *mon, const QDict *qdict)
                        info->ram->total >> 10);
         monitor_printf(mon, "duplicate: %" PRIu64 " pages\n",
                        info->ram->duplicate);
+        monitor_printf(mon, "skipped: %" PRIu64 " pages\n",
+                       info->ram->skipped);
         monitor_printf(mon, "normal: %" PRIu64 " pages\n",
                        info->ram->normal);
         monitor_printf(mon, "normal bytes: %" PRIu64 " kbytes\n",

diff --git a/include/migration/migration.h b/include/migration/migration.h
index bb617fdacf111b91c1e97de438158115c0f074b2..e2acec64c0b1c95e53fdccaa2a64657509bb9d06 100644 (file)
--- a/include/migration/migration.h
+++ b/include/migration/migration.h
@@ -96,6 +96,8 @@ extern SaveVMHandlers savevm_ram_handlers;
 
 uint64_t dup_mig_bytes_transferred(void);
 uint64_t dup_mig_pages_transferred(void);
+uint64_t skipped_mig_bytes_transferred(void);
+uint64_t skipped_mig_pages_transferred(void);
 uint64_t norm_mig_bytes_transferred(void);
 uint64_t norm_mig_pages_transferred(void);
 uint64_t xbzrle_mig_bytes_transferred(void);

diff --git a/migration.c b/migration.c
index 185d11260d9e6d31fb5906eb741189c7dc624583..7fb21473916b2e04f79834a3de242adcac456462 100644 (file)
--- a/migration.c
+++ b/migration.c
@@ -197,11 +197,11 @@ MigrationInfo *qmp_query_migrate(Error **errp)
         info->ram->remaining = ram_bytes_remaining();
         info->ram->total = ram_bytes_total();
         info->ram->duplicate = dup_mig_pages_transferred();
+        info->ram->skipped = skipped_mig_pages_transferred();
         info->ram->normal = norm_mig_pages_transferred();
         info->ram->normal_bytes = norm_mig_bytes_transferred();
         info->ram->dirty_pages_rate = s->dirty_pages_rate;
 
-
         if (blk_mig_active()) {
             info->has_disk = true;
             info->disk = g_malloc0(sizeof(*info->disk));
@@ -227,6 +227,7 @@ MigrationInfo *qmp_query_migrate(Error **errp)
         info->ram->remaining = 0;
         info->ram->total = ram_bytes_total();
         info->ram->duplicate = dup_mig_pages_transferred();
+        info->ram->skipped = skipped_mig_pages_transferred();
         info->ram->normal = norm_mig_pages_transferred();
         info->ram->normal_bytes = norm_mig_bytes_transferred();
         break;

diff --git a/qapi-schema.json b/qapi-schema.json
index 088f4e150fc1a068c6b5240506bb251b544d605a..6c4966be43afcdfa6554d174633b067cacce58e1 100644 (file)
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -496,7 +496,9 @@
 #
 # @total: total amount of bytes involved in the migration process
 #
-# @duplicate: number of duplicate pages (since 1.2)
+# @duplicate: number of duplicate (zero) pages (since 1.2)
+#
+# @skipped: number of skipped zero pages (since 1.5)
 #
 # @normal : number of normal pages (since 1.2)
 #
@@ -509,8 +511,8 @@
 ##
 { 'type': 'MigrationStats',
   'data': {'transferred': 'int', 'remaining': 'int', 'total': 'int' ,
-           'duplicate': 'int', 'normal': 'int', 'normal-bytes': 'int',
-           'dirty-pages-rate' : 'int' } }
+           'duplicate': 'int', 'skipped': 'int', 'normal': 'int',
+           'normal-bytes': 'int', 'dirty-pages-rate' : 'int' } }
 
 ##
 # @XBZRLECacheStats

diff --git a/qmp-commands.hx b/qmp-commands.hx
index 5e847b18d9137fb9989ede279ced7f44bc2edb40..fdc40486f68836b76a57e5d3babacb73e0bf3b68 100644 (file)
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -2445,6 +2445,7 @@ The main json-object contains the following:
          - "duplicate": number of pages filled entirely with the same
             byte (json-int)
             These are sent over the wire much more efficiently.
+         - "skipped": number of skipped zero pages (json-int)
          - "normal" : number of whole pages transfered.  I.e. they
             were not sent as duplicate or xbzrle pages (json-int)
          - "normal-bytes" : number of bytes transferred in whole