[PATCH 00/11] Multifd zero page support

[PATCH 00/11] Multifd zero page support

[Juan Quintela]

Based on top of my next-8.0 branch.

- rebased on top of latest upstream
- lots of minor fixes
- start support for atomic counters
  * we need to move ram_limit_used/max to migration.c
  * that means fixing rdma.c
  * and test-vmstate.

So I am donig that right now.

Juan Quintela (11):
  migration: Update atomic stats out of the mutex
  migration: Make multifd_bytes atomic
  multifd: We already account for this packet on the multifd thread
  multifd: Count the number of bytes sent correctly
  migration: Make ram_save_target_page() a pointer
  multifd: Make flags field thread local
  multifd: Prepare to send a packet without the mutex held
  multifd: Add capability to enable/disable zero_page
  multifd: Support for zero pages transmission
  multifd: Zero pages transmission
  So we use multifd to transmit zero pages.

 qapi/migration.json    |   8 ++-
 migration/migration.h  |   1 +
 migration/multifd.h    |  36 ++++++++++--
 migration/ram.h        |   1 +
 hw/core/machine.c      |   1 +
 migration/migration.c  |  16 +++++-
 migration/multifd.c    | 123 +++++++++++++++++++++++++++++++----------
 migration/ram.c        |  51 +++++++++++++++--
 migration/trace-events |   8 +--
 9 files changed, 197 insertions(+), 48 deletions(-)

-- 
2.38.1

[PATCH 01/11] migration: Update atomic stats out of the mutex

[Juan Quintela]

Signed-off-by: Juan Quintela <quintela@redhat.com>
---
 migration/multifd.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/migration/multifd.c b/migration/multifd.c
index 000ca4d4ec..20a81cd7f2 100644
--- a/migration/multifd.c
+++ b/migration/multifd.c
@@ -432,8 +432,8 @@ static int multifd_send_pages(QEMUFile *f)
     transferred = ((uint64_t) pages->num) * p->page_size + p->packet_len;
     qemu_file_acct_rate_limit(f, transferred);
     ram_counters.multifd_bytes += transferred;
+    qemu_mutex_unlock(&p->mutex);
     stat64_add(&ram_atomic_counters.transferred, transferred);
-    qemu_mutex_unlock(&p->mutex);
     qemu_sem_post(&p->sem);
 
     return 1;
@@ -624,8 +624,8 @@ int multifd_send_sync_main(QEMUFile *f)
         p->pending_job++;
         qemu_file_acct_rate_limit(f, p->packet_len);
         ram_counters.multifd_bytes += p->packet_len;
+        qemu_mutex_unlock(&p->mutex);
         stat64_add(&ram_atomic_counters.transferred, p->packet_len);
-        qemu_mutex_unlock(&p->mutex);
         qemu_sem_post(&p->sem);
 
         if (flush_zero_copy && p->c && (multifd_zero_copy_flush(p->c) < 0)) {
-- 
2.38.1

[PATCH 02/11] migration: Make multifd_bytes atomic

[Juan Quintela]

In the spirit of:

commit 394d323bc3451e4d07f13341cb8817fac8dfbadd
Author: Peter Xu <peterx@redhat.com>
Date:   Tue Oct 11 17:55:51 2022 -0400

    migration: Use atomic ops properly for page accountings

Signed-off-by: Juan Quintela <quintela@redhat.com>
---
 migration/ram.h       | 1 +
 migration/migration.c | 4 ++--
 migration/multifd.c   | 4 ++--
 3 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/migration/ram.h b/migration/ram.h
index 81cbb0947c..3c1de6aedf 100644
--- a/migration/ram.h
+++ b/migration/ram.h
@@ -50,6 +50,7 @@ typedef struct {
     Stat64 duplicate;
     Stat64 normal;
     Stat64 postcopy_bytes;
+    Stat64 multifd_bytes;
 } MigrationAtomicStats;
 
 extern MigrationAtomicStats ram_atomic_counters;
diff --git a/migration/migration.c b/migration/migration.c
index c3490c495d..d5733b7c03 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -1062,7 +1062,7 @@ static void populate_ram_info(MigrationInfo *info, MigrationState *s)
             ram_counters.dirty_sync_missed_zero_copy;
     info->ram->postcopy_requests = ram_counters.postcopy_requests;
     info->ram->page_size = page_size;
-    info->ram->multifd_bytes = ram_counters.multifd_bytes;
+    info->ram->multifd_bytes = stat64_get(&ram_atomic_counters.multifd_bytes);
     info->ram->pages_per_second = s->pages_per_second;
     info->ram->precopy_bytes = ram_counters.precopy_bytes;
     info->ram->downtime_bytes = ram_counters.downtime_bytes;
@@ -3667,7 +3667,7 @@ static MigThrError migration_detect_error(MigrationState *s)
 static uint64_t migration_total_bytes(MigrationState *s)
 {
     return qemu_file_total_transferred(s->to_dst_file) +
-        ram_counters.multifd_bytes;
+        stat64_get(&ram_atomic_counters.multifd_bytes);
 }
 
 static void migration_calculate_complete(MigrationState *s)
diff --git a/migration/multifd.c b/migration/multifd.c
index 20a81cd7f2..49fa76e5e1 100644
--- a/migration/multifd.c
+++ b/migration/multifd.c
@@ -431,8 +431,8 @@ static int multifd_send_pages(QEMUFile *f)
     p->pages = pages;
     transferred = ((uint64_t) pages->num) * p->page_size + p->packet_len;
     qemu_file_acct_rate_limit(f, transferred);
-    ram_counters.multifd_bytes += transferred;
     qemu_mutex_unlock(&p->mutex);
+    stat64_add(&ram_atomic_counters.multifd_bytes, transferred);
     stat64_add(&ram_atomic_counters.transferred, transferred);
     qemu_sem_post(&p->sem);
 
@@ -623,8 +623,8 @@ int multifd_send_sync_main(QEMUFile *f)
         p->flags |= MULTIFD_FLAG_SYNC;
         p->pending_job++;
         qemu_file_acct_rate_limit(f, p->packet_len);
-        ram_counters.multifd_bytes += p->packet_len;
         qemu_mutex_unlock(&p->mutex);
+        stat64_add(&ram_atomic_counters.multifd_bytes, p->packet_len);
         stat64_add(&ram_atomic_counters.transferred, p->packet_len);
         qemu_sem_post(&p->sem);
 
-- 
2.38.1

[PATCH 03/11] multifd: We already account for this packet on the multifd thread

[Juan Quintela]

Signed-off-by: Juan Quintela <quintela@redhat.com>
---
 migration/multifd.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/migration/multifd.c b/migration/multifd.c
index 49fa76e5e1..61cafe4c76 100644
--- a/migration/multifd.c
+++ b/migration/multifd.c
@@ -622,10 +622,7 @@ int multifd_send_sync_main(QEMUFile *f)
         p->packet_num = multifd_send_state->packet_num++;
         p->flags |= MULTIFD_FLAG_SYNC;
         p->pending_job++;
-        qemu_file_acct_rate_limit(f, p->packet_len);
         qemu_mutex_unlock(&p->mutex);
-        stat64_add(&ram_atomic_counters.multifd_bytes, p->packet_len);
-        stat64_add(&ram_atomic_counters.transferred, p->packet_len);
         qemu_sem_post(&p->sem);
 
         if (flush_zero_copy && p->c && (multifd_zero_copy_flush(p->c) < 0)) {
-- 
2.38.1

[PATCH 04/11] multifd: Count the number of bytes sent correctly

[Juan Quintela]

Current code asumes that all pages are whole.  That is not true for
example for compression already.  Fix it for creating a new field
->sent_bytes that includes it.

All ram_counters are used only from the migration thread, so we have
two options:
- put a mutex and fill everything when we sent it (not only
  ram_counters, also qemu_file->xfer_bytes).
- Create a local variable that implements how much has been sent
  through each channel.  And when we push another packet, we "add" the
  previous stats.

I choose two due to less changes overall.  On the previous code we
increase transferred and then we sent.  Current code goes the other
way around.  It sents the data, and after the fact, it updates the
counters.  Notice that each channel can have a maximum of half a
megabyte of data without counting, so it is not very important.

Signed-off-by: Juan Quintela <quintela@redhat.com>
---
 migration/multifd.h | 2 ++
 migration/multifd.c | 6 ++++--
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/migration/multifd.h b/migration/multifd.h
index e2802a9ce2..36f899c56f 100644
--- a/migration/multifd.h
+++ b/migration/multifd.h
@@ -102,6 +102,8 @@ typedef struct {
     uint32_t flags;
     /* global number of generated multifd packets */
     uint64_t packet_num;
+    /* How many bytes have we sent on the last packet */
+    uint64_t sent_bytes;
     /* thread has work to do */
     int pending_job;
     /* array of pages to sent.
diff --git a/migration/multifd.c b/migration/multifd.c
index 61cafe4c76..cd26b2fda9 100644
--- a/migration/multifd.c
+++ b/migration/multifd.c
@@ -394,7 +394,6 @@ static int multifd_send_pages(QEMUFile *f)
     static int next_channel;
     MultiFDSendParams *p = NULL; /* make happy gcc */
     MultiFDPages_t *pages = multifd_send_state->pages;
-    uint64_t transferred;
 
     if (qatomic_read(&multifd_send_state->exiting)) {
         return -1;
@@ -429,7 +428,8 @@ static int multifd_send_pages(QEMUFile *f)
     p->packet_num = multifd_send_state->packet_num++;
     multifd_send_state->pages = p->pages;
     p->pages = pages;
-    transferred = ((uint64_t) pages->num) * p->page_size + p->packet_len;
+    uint64_t transferred = p->sent_bytes;
+    p->sent_bytes = 0;
     qemu_file_acct_rate_limit(f, transferred);
     qemu_mutex_unlock(&p->mutex);
     stat64_add(&ram_atomic_counters.multifd_bytes, transferred);
@@ -719,6 +719,8 @@ static void *multifd_send_thread(void *opaque)
             }
 
             qemu_mutex_lock(&p->mutex);
+            p->sent_bytes += p->packet_len;
+            p->sent_bytes += p->next_packet_size;
             p->pending_job--;
             qemu_mutex_unlock(&p->mutex);
 
-- 
2.38.1

[PATCH 05/11] migration: Make ram_save_target_page() a pointer

[Juan Quintela]

We are going to create a new function for multifd latest in the series.

Signed-off-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
---
 migration/ram.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/migration/ram.c b/migration/ram.c
index 334309f1c6..48cbba3173 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -450,6 +450,13 @@ void dirty_sync_missed_zero_copy(void)
     ram_counters.dirty_sync_missed_zero_copy++;
 }
 
+struct MigrationOps {
+    int (*ram_save_target_page)(RAMState *rs, PageSearchStatus *pss);
+};
+typedef struct MigrationOps MigrationOps;
+
+MigrationOps *migration_ops;
+
 CompressionStats compression_counters;
 
 struct CompressParam {
@@ -2265,14 +2272,14 @@ static bool save_compress_page(RAMState *rs, PageSearchStatus *pss,
 }
 
 /**
- * ram_save_target_page: save one target page
+ * ram_save_target_page_legacy: save one target page
  *
  * Returns the number of pages written
  *
  * @rs: current RAM state
  * @pss: data about the page we want to send
  */
-static int ram_save_target_page(RAMState *rs, PageSearchStatus *pss)
+static int ram_save_target_page_legacy(RAMState *rs, PageSearchStatus *pss)
 {
     RAMBlock *block = pss->block;
     ram_addr_t offset = ((ram_addr_t)pss->page) << TARGET_PAGE_BITS;
@@ -2381,7 +2388,7 @@ static int ram_save_host_page_urgent(PageSearchStatus *pss)
 
         if (page_dirty) {
             /* Be strict to return code; it must be 1, or what else? */
-            if (ram_save_target_page(rs, pss) != 1) {
+            if (migration_ops->ram_save_target_page(rs, pss) != 1) {
                 error_report_once("%s: ram_save_target_page failed", __func__);
                 ret = -1;
                 goto out;
@@ -2450,7 +2457,7 @@ static int ram_save_host_page(RAMState *rs, PageSearchStatus *pss)
             if (preempt_active) {
                 qemu_mutex_unlock(&rs->bitmap_mutex);
             }
-            tmppages = ram_save_target_page(rs, pss);
+            tmppages = migration_ops->ram_save_target_page(rs, pss);
             if (tmppages >= 0) {
                 pages += tmppages;
                 /*
@@ -2645,6 +2652,8 @@ static void ram_save_cleanup(void *opaque)
     xbzrle_cleanup();
     compress_threads_save_cleanup();
     ram_state_cleanup(rsp);
+    g_free(migration_ops);
+    migration_ops = NULL;
 }
 
 static void ram_state_reset(RAMState *rs)
@@ -3198,6 +3207,8 @@ static int ram_save_setup(QEMUFile *f, void *opaque)
     ram_control_before_iterate(f, RAM_CONTROL_SETUP);
     ram_control_after_iterate(f, RAM_CONTROL_SETUP);
 
+    migration_ops = g_malloc0(sizeof(MigrationOps));
+    migration_ops->ram_save_target_page = ram_save_target_page_legacy;
     ret =  multifd_send_sync_main(f);
     if (ret < 0) {
         return ret;
-- 
2.38.1

[PATCH 06/11] multifd: Make flags field thread local

[Juan Quintela]

Use of flags with respect to locking was incensistant.  For the
sending side:
- it was set to 0 with mutex held on the multifd channel.
- MULTIFD_FLAG_SYNC was set with mutex held on the migration thread.
- Everything else was done without the mutex held on the multifd channel.

On the reception side, it is not used on the migration thread, only on
the multifd channels threads.

So we move it to the multifd channels thread only variables, and we
introduce a new bool sync_needed on the send side to pass that information.

Signed-off-by: Juan Quintela <quintela@redhat.com>
---
 migration/multifd.h | 10 ++++++----
 migration/multifd.c | 23 +++++++++++++----------
 2 files changed, 19 insertions(+), 14 deletions(-)

diff --git a/migration/multifd.h b/migration/multifd.h
index 36f899c56f..a67cefc0a2 100644
--- a/migration/multifd.h
+++ b/migration/multifd.h
@@ -98,12 +98,12 @@ typedef struct {
     bool running;
     /* should this thread finish */
     bool quit;
-    /* multifd flags for each packet */
-    uint32_t flags;
     /* global number of generated multifd packets */
     uint64_t packet_num;
     /* How many bytes have we sent on the last packet */
     uint64_t sent_bytes;
+    /* Do we need to do an iteration sync */
+    bool sync_needed;
     /* thread has work to do */
     int pending_job;
     /* array of pages to sent.
@@ -117,6 +117,8 @@ typedef struct {
 
     /* pointer to the packet */
     MultiFDPacket_t *packet;
+    /* multifd flags for each packet */
+    uint32_t flags;
     /* size of the next packet that contains pages */
     uint32_t next_packet_size;
     /* packets sent through this channel */
@@ -163,8 +165,6 @@ typedef struct {
     bool running;
     /* should this thread finish */
     bool quit;
-    /* multifd flags for each packet */
-    uint32_t flags;
     /* global number of generated multifd packets */
     uint64_t packet_num;
 
@@ -172,6 +172,8 @@ typedef struct {
 
     /* pointer to the packet */
     MultiFDPacket_t *packet;
+    /* multifd flags for each packet */
+    uint32_t flags;
     /* size of the next packet that contains pages */
     uint32_t next_packet_size;
     /* packets sent through this channel */
diff --git a/migration/multifd.c b/migration/multifd.c
index cd26b2fda9..77196a55b4 100644
--- a/migration/multifd.c
+++ b/migration/multifd.c
@@ -620,7 +620,7 @@ int multifd_send_sync_main(QEMUFile *f)
         }
 
         p->packet_num = multifd_send_state->packet_num++;
-        p->flags |= MULTIFD_FLAG_SYNC;
+        p->sync_needed = true;
         p->pending_job++;
         qemu_mutex_unlock(&p->mutex);
         qemu_sem_post(&p->sem);
@@ -667,7 +667,11 @@ static void *multifd_send_thread(void *opaque)
 
         if (p->pending_job) {
             uint64_t packet_num = p->packet_num;
-            uint32_t flags = p->flags;
+            p->flags = 0;
+            if (p->sync_needed) {
+                p->flags |= MULTIFD_FLAG_SYNC;
+                p->sync_needed = false;
+            }
             p->normal_num = 0;
 
             if (use_zero_copy_send) {
@@ -689,14 +693,13 @@ static void *multifd_send_thread(void *opaque)
                 }
             }
             multifd_send_fill_packet(p);
-            p->flags = 0;
             p->num_packets++;
             p->total_normal_pages += p->normal_num;
             p->pages->num = 0;
             p->pages->block = NULL;
             qemu_mutex_unlock(&p->mutex);
 
-            trace_multifd_send(p->id, packet_num, p->normal_num, flags,
+            trace_multifd_send(p->id, packet_num, p->normal_num, p->flags,
                                p->next_packet_size);
 
             if (use_zero_copy_send) {
@@ -724,7 +727,7 @@ static void *multifd_send_thread(void *opaque)
             p->pending_job--;
             qemu_mutex_unlock(&p->mutex);
 
-            if (flags & MULTIFD_FLAG_SYNC) {
+            if (p->flags & MULTIFD_FLAG_SYNC) {
                 qemu_sem_post(&p->sem_sync);
             }
             qemu_sem_post(&multifd_send_state->channels_ready);
@@ -1099,7 +1102,7 @@ static void *multifd_recv_thread(void *opaque)
     rcu_register_thread();
 
     while (true) {
-        uint32_t flags;
+        bool sync_needed = false;
 
         if (p->quit) {
             break;
@@ -1121,11 +1124,11 @@ static void *multifd_recv_thread(void *opaque)
             break;
         }
 
-        flags = p->flags;
+        trace_multifd_recv(p->id, p->packet_num, p->normal_num, p->flags,
+                           p->next_packet_size);
+        sync_needed = p->flags & MULTIFD_FLAG_SYNC;
         /* recv methods don't know how to handle the SYNC flag */
         p->flags &= ~MULTIFD_FLAG_SYNC;
-        trace_multifd_recv(p->id, p->packet_num, p->normal_num, flags,
-                           p->next_packet_size);
         p->num_packets++;
         p->total_normal_pages += p->normal_num;
         qemu_mutex_unlock(&p->mutex);
@@ -1137,7 +1140,7 @@ static void *multifd_recv_thread(void *opaque)
             }
         }
 
-        if (flags & MULTIFD_FLAG_SYNC) {
+        if (sync_needed) {
             qemu_sem_post(&multifd_recv_state->sem_sync);
             qemu_sem_wait(&p->sem_sync);
         }
-- 
2.38.1

[PATCH 07/11] multifd: Prepare to send a packet without the mutex held

[Juan Quintela]

We do the send_prepare() and the fill of the head packet without the
mutex held.  It will help a lot for compression and later in the
series for zero pages.

Notice that we can use p->pages without holding p->mutex because
p->pending_job == 1.

Signed-off-by: Juan Quintela <quintela@redhat.com>
---
 migration/multifd.h |  2 ++
 migration/multifd.c | 12 ++++++------
 2 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/migration/multifd.h b/migration/multifd.h
index a67cefc0a2..cd389d18d2 100644
--- a/migration/multifd.h
+++ b/migration/multifd.h
@@ -109,7 +109,9 @@ typedef struct {
     /* array of pages to sent.
      * The owner of 'pages' depends of 'pending_job' value:
      * pending_job == 0 -> migration_thread can use it.
+     *                     No need for mutex lock.
      * pending_job != 0 -> multifd_channel can use it.
+     *                     No need for mutex lock.
      */
     MultiFDPages_t *pages;
 
diff --git a/migration/multifd.c b/migration/multifd.c
index 77196a55b4..7ebaca6e55 100644
--- a/migration/multifd.c
+++ b/migration/multifd.c
@@ -672,6 +672,8 @@ static void *multifd_send_thread(void *opaque)
                 p->flags |= MULTIFD_FLAG_SYNC;
                 p->sync_needed = false;
             }
+            qemu_mutex_unlock(&p->mutex);
+
             p->normal_num = 0;
 
             if (use_zero_copy_send) {
@@ -688,16 +690,10 @@ static void *multifd_send_thread(void *opaque)
             if (p->normal_num) {
                 ret = multifd_send_state->ops->send_prepare(p, &local_err);
                 if (ret != 0) {
-                    qemu_mutex_unlock(&p->mutex);
                     break;
                 }
             }
             multifd_send_fill_packet(p);
-            p->num_packets++;
-            p->total_normal_pages += p->normal_num;
-            p->pages->num = 0;
-            p->pages->block = NULL;
-            qemu_mutex_unlock(&p->mutex);
 
             trace_multifd_send(p->id, packet_num, p->normal_num, p->flags,
                                p->next_packet_size);
@@ -722,6 +718,10 @@ static void *multifd_send_thread(void *opaque)
             }
 
             qemu_mutex_lock(&p->mutex);
+            p->num_packets++;
+            p->total_normal_pages += p->normal_num;
+            p->pages->num = 0;
+            p->pages->block = NULL;
             p->sent_bytes += p->packet_len;
             p->sent_bytes += p->next_packet_size;
             p->pending_job--;
-- 
2.38.1

[PATCH 08/11] multifd: Add capability to enable/disable zero_page

[Juan Quintela]

We have to enable it by default until we introduce the new code.

Signed-off-by: Juan Quintela <quintela@redhat.com>

---

Change it to a capability.  As capabilities are off by default, have
to change MULTIFD_ZERO_PAGE to MAIN_ZERO_PAGE, so it is false for
default, and true for older versions.
---
 qapi/migration.json   |  8 +++++++-
 migration/migration.h |  1 +
 hw/core/machine.c     |  1 +
 migration/migration.c | 13 ++++++++++++-
 4 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/qapi/migration.json b/qapi/migration.json
index 88ecf86ac8..ac5bc071a9 100644
--- a/qapi/migration.json
+++ b/qapi/migration.json
@@ -472,12 +472,18 @@
 #                  Requires that QEMU be permitted to use locked memory
 #                  for guest RAM pages.
 #                  (since 7.1)
+#
 # @postcopy-preempt: If enabled, the migration process will allow postcopy
 #                    requests to preempt precopy stream, so postcopy requests
 #                    will be handled faster.  This is a performance feature and
 #                    should not affect the correctness of postcopy migration.
 #                    (since 7.1)
 #
+# @main-zero-page: If enabled, the detection of zero pages will be
+#                  done on the main thread.  Otherwise it is done on
+#                  the multifd threads.
+#                  (since 8.0)
+#
 # Features:
 # @unstable: Members @x-colo and @x-ignore-shared are experimental.
 #
@@ -492,7 +498,7 @@
            'dirty-bitmaps', 'postcopy-blocktime', 'late-block-activate',
            { 'name': 'x-ignore-shared', 'features': [ 'unstable' ] },
            'validate-uuid', 'background-snapshot',
-           'zero-copy-send', 'postcopy-preempt'] }
+           'zero-copy-send', 'postcopy-preempt', 'main-zero-page'] }
 
 ##
 # @MigrationCapabilityStatus:
diff --git a/migration/migration.h b/migration/migration.h
index ae4ffd3454..c38a0baf10 100644
--- a/migration/migration.h
+++ b/migration/migration.h
@@ -408,6 +408,7 @@ int migrate_multifd_channels(void);
 MultiFDCompression migrate_multifd_compression(void);
 int migrate_multifd_zlib_level(void);
 int migrate_multifd_zstd_level(void);
+bool migrate_use_main_zero_page(void);
 
 #ifdef CONFIG_LINUX
 bool migrate_use_zero_copy_send(void);
diff --git a/hw/core/machine.c b/hw/core/machine.c
index 8d34caa31d..cdc9c1e2a3 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -48,6 +48,7 @@ const size_t hw_compat_7_1_len = G_N_ELEMENTS(hw_compat_7_1);
 GlobalProperty hw_compat_7_0[] = {
     { "arm-gicv3-common", "force-8-bit-prio", "on" },
     { "nvme-ns", "eui64-default", "on"},
+    { "migration", "main-zero-page", "true" },
 };
 const size_t hw_compat_7_0_len = G_N_ELEMENTS(hw_compat_7_0);
 
diff --git a/migration/migration.c b/migration/migration.c
index d5733b7c03..2a828764ed 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -164,7 +164,8 @@ INITIALIZE_MIGRATE_CAPS_SET(check_caps_background_snapshot,
     MIGRATION_CAPABILITY_XBZRLE,
     MIGRATION_CAPABILITY_X_COLO,
     MIGRATION_CAPABILITY_VALIDATE_UUID,
-    MIGRATION_CAPABILITY_ZERO_COPY_SEND);
+    MIGRATION_CAPABILITY_ZERO_COPY_SEND,
+    MIGRATION_CAPABILITY_MAIN_ZERO_PAGE);
 
 /* When we add fault tolerance, we could have several
    migrations at once.  For now we don't need to add
@@ -2611,6 +2612,14 @@ bool migrate_use_multifd(void)
     return s->enabled_capabilities[MIGRATION_CAPABILITY_MULTIFD];
 }
 
+bool migrate_use_main_zero_page(void)
+{
+    MigrationState *s = migrate_get_current();
+
+    /* We will enable this when we add the right code. */
+    return true || s->enabled_capabilities[MIGRATION_CAPABILITY_MAIN_ZERO_PAGE];
+}
+
 bool migrate_pause_before_switchover(void)
 {
     MigrationState *s;
@@ -4427,6 +4436,8 @@ static Property migration_properties[] = {
     DEFINE_PROP_MIG_CAP("x-zero-copy-send",
             MIGRATION_CAPABILITY_ZERO_COPY_SEND),
 #endif
+    DEFINE_PROP_MIG_CAP("main-zero-page",
+            MIGRATION_CAPABILITY_MAIN_ZERO_PAGE),
 
     DEFINE_PROP_END_OF_LIST(),
 };
-- 
2.38.1

[PATCH 09/11] multifd: Support for zero pages transmission

[Juan Quintela]

This patch adds counters and similar.  Logic will be added on the
following patch.

Signed-off-by: Juan Quintela <quintela@redhat.com>

---

Added counters for duplicated/non duplicated pages.
Removed reviewed by from David.
Add total_zero_pages
---
 migration/multifd.h    | 17 ++++++++++++++++-
 migration/multifd.c    | 36 +++++++++++++++++++++++++++++-------
 migration/ram.c        |  2 --
 migration/trace-events |  8 ++++----
 4 files changed, 49 insertions(+), 14 deletions(-)

diff --git a/migration/multifd.h b/migration/multifd.h
index cd389d18d2..a1b852200d 100644
--- a/migration/multifd.h
+++ b/migration/multifd.h
@@ -47,7 +47,10 @@ typedef struct {
     /* size of the next packet that contains pages */
     uint32_t next_packet_size;
     uint64_t packet_num;
-    uint64_t unused[4];    /* Reserved for future use */
+    /* zero pages */
+    uint32_t zero_pages;
+    uint32_t unused32[1];    /* Reserved for future use */
+    uint64_t unused64[3];    /* Reserved for future use */
     char ramblock[256];
     uint64_t offset[];
 } __attribute__((packed)) MultiFDPacket_t;
@@ -127,6 +130,8 @@ typedef struct {
     uint64_t num_packets;
     /* non zero pages sent through this channel */
     uint64_t total_normal_pages;
+    /* zero pages sent through this channel */
+    uint64_t total_zero_pages;
     /* buffers to send */
     struct iovec *iov;
     /* number of iovs used */
@@ -135,6 +140,10 @@ typedef struct {
     ram_addr_t *normal;
     /* num of non zero pages */
     uint32_t normal_num;
+    /* Pages that are  zero */
+    ram_addr_t *zero;
+    /* num of zero pages */
+    uint32_t zero_num;
     /* used for compression methods */
     void *data;
 }  MultiFDSendParams;
@@ -184,12 +193,18 @@ typedef struct {
     uint8_t *host;
     /* non zero pages recv through this channel */
     uint64_t total_normal_pages;
+    /* zero pages recv through this channel */
+    uint64_t total_zero_pages;
     /* buffers to recv */
     struct iovec *iov;
     /* Pages that are not zero */
     ram_addr_t *normal;
     /* num of non zero pages */
     uint32_t normal_num;
+    /* Pages that are  zero */
+    ram_addr_t *zero;
+    /* num of zero pages */
+    uint32_t zero_num;
     /* used for de-compression methods */
     void *data;
 } MultiFDRecvParams;
diff --git a/migration/multifd.c b/migration/multifd.c
index 7ebaca6e55..30cc206190 100644
--- a/migration/multifd.c
+++ b/migration/multifd.c
@@ -263,6 +263,7 @@ static void multifd_send_fill_packet(MultiFDSendParams *p)
     packet->normal_pages = cpu_to_be32(p->normal_num);
     packet->next_packet_size = cpu_to_be32(p->next_packet_size);
     packet->packet_num = cpu_to_be64(p->packet_num);
+    packet->zero_pages = cpu_to_be32(p->zero_num);
 
     if (p->pages->block) {
         strncpy(packet->ramblock, p->pages->block->idstr, 256);
@@ -323,7 +324,15 @@ static int multifd_recv_unfill_packet(MultiFDRecvParams *p, Error **errp)
     p->next_packet_size = be32_to_cpu(packet->next_packet_size);
     p->packet_num = be64_to_cpu(packet->packet_num);
 
-    if (p->normal_num == 0) {
+    p->zero_num = be32_to_cpu(packet->zero_pages);
+    if (p->zero_num > packet->pages_alloc - p->normal_num) {
+        error_setg(errp, "multifd: received packet "
+                   "with %u zero pages and expected maximum pages are %u",
+                   p->zero_num, packet->pages_alloc - p->normal_num) ;
+        return -1;
+    }
+
+    if (p->normal_num == 0 && p->zero_num == 0) {
         return 0;
     }
 
@@ -428,6 +437,8 @@ static int multifd_send_pages(QEMUFile *f)
     p->packet_num = multifd_send_state->packet_num++;
     multifd_send_state->pages = p->pages;
     p->pages = pages;
+    stat64_add(&ram_atomic_counters.normal, p->normal_num);
+    stat64_add(&ram_atomic_counters.duplicate, p->zero_num);
     uint64_t transferred = p->sent_bytes;
     p->sent_bytes = 0;
     qemu_file_acct_rate_limit(f, transferred);
@@ -546,6 +557,8 @@ void multifd_save_cleanup(void)
         p->iov = NULL;
         g_free(p->normal);
         p->normal = NULL;
+        g_free(p->zero);
+        p->zero = NULL;
         multifd_send_state->ops->send_cleanup(p, &local_err);
         if (local_err) {
             migrate_set_error(migrate_get_current(), local_err);
@@ -675,6 +688,7 @@ static void *multifd_send_thread(void *opaque)
             qemu_mutex_unlock(&p->mutex);
 
             p->normal_num = 0;
+            p->zero_num = 0;
 
             if (use_zero_copy_send) {
                 p->iovs_num = 0;
@@ -695,8 +709,8 @@ static void *multifd_send_thread(void *opaque)
             }
             multifd_send_fill_packet(p);
 
-            trace_multifd_send(p->id, packet_num, p->normal_num, p->flags,
-                               p->next_packet_size);
+            trace_multifd_send(p->id, packet_num, p->normal_num, p->zero_num,
+                               p->flags, p->next_packet_size);
 
             if (use_zero_copy_send) {
                 /* Send header first, without zerocopy */
@@ -720,6 +734,7 @@ static void *multifd_send_thread(void *opaque)
             qemu_mutex_lock(&p->mutex);
             p->num_packets++;
             p->total_normal_pages += p->normal_num;
+            p->total_zero_pages += p->zero_num;
             p->pages->num = 0;
             p->pages->block = NULL;
             p->sent_bytes += p->packet_len;
@@ -761,7 +776,8 @@ out:
     qemu_mutex_unlock(&p->mutex);
 
     rcu_unregister_thread();
-    trace_multifd_send_thread_end(p->id, p->num_packets, p->total_normal_pages);
+    trace_multifd_send_thread_end(p->id, p->num_packets, p->total_normal_pages,
+                                  p->total_zero_pages);
 
     return NULL;
 }
@@ -946,6 +962,7 @@ int multifd_save_setup(Error **errp)
         p->normal = g_new0(ram_addr_t, page_count);
         p->page_size = qemu_target_page_size();
         p->page_count = page_count;
+        p->zero = g_new0(ram_addr_t, page_count);
 
         if (migrate_use_zero_copy_send()) {
             p->write_flags = QIO_CHANNEL_WRITE_FLAG_ZERO_COPY;
@@ -1054,6 +1071,8 @@ int multifd_load_cleanup(Error **errp)
         p->iov = NULL;
         g_free(p->normal);
         p->normal = NULL;
+        g_free(p->zero);
+        p->zero = NULL;
         multifd_recv_state->ops->recv_cleanup(p);
     }
     qemu_sem_destroy(&multifd_recv_state->sem_sync);
@@ -1124,13 +1143,14 @@ static void *multifd_recv_thread(void *opaque)
             break;
         }
 
-        trace_multifd_recv(p->id, p->packet_num, p->normal_num, p->flags,
-                           p->next_packet_size);
+        trace_multifd_recv(p->id, p->packet_num, p->normal_num, p->zero_num,
+                           p->flags, p->next_packet_size);
         sync_needed = p->flags & MULTIFD_FLAG_SYNC;
         /* recv methods don't know how to handle the SYNC flag */
         p->flags &= ~MULTIFD_FLAG_SYNC;
         p->num_packets++;
         p->total_normal_pages += p->normal_num;
+        p->total_normal_pages += p->zero_num;
         qemu_mutex_unlock(&p->mutex);
 
         if (p->normal_num) {
@@ -1155,7 +1175,8 @@ static void *multifd_recv_thread(void *opaque)
     qemu_mutex_unlock(&p->mutex);
 
     rcu_unregister_thread();
-    trace_multifd_recv_thread_end(p->id, p->num_packets, p->total_normal_pages);
+    trace_multifd_recv_thread_end(p->id, p->num_packets, p->total_normal_pages,
+                                  p->total_zero_pages);
 
     return NULL;
 }
@@ -1195,6 +1216,7 @@ int multifd_load_setup(Error **errp)
         p->normal = g_new0(ram_addr_t, page_count);
         p->page_count = page_count;
         p->page_size = qemu_target_page_size();
+        p->zero = g_new0(ram_addr_t, page_count);
     }
 
     for (i = 0; i < thread_count; i++) {
diff --git a/migration/ram.c b/migration/ram.c
index 48cbba3173..f23a01719b 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -1426,8 +1426,6 @@ static int ram_save_multifd_page(QEMUFile *file, RAMBlock *block,
     if (multifd_queue_page(file, block, offset) < 0) {
         return -1;
     }
-    stat64_add(&ram_atomic_counters.normal, 1);
-
     return 1;
 }
 
diff --git a/migration/trace-events b/migration/trace-events
index 57003edcbd..0facbb07f0 100644
--- a/migration/trace-events
+++ b/migration/trace-events
@@ -121,21 +121,21 @@ postcopy_preempt_reset_channel(void) ""
 
 # multifd.c
 multifd_new_send_channel_async(uint8_t id) "channel %u"
-multifd_recv(uint8_t id, uint64_t packet_num, uint32_t used, uint32_t flags, uint32_t next_packet_size) "channel %u packet_num %" PRIu64 " pages %u flags 0x%x next packet size %u"
+multifd_recv(uint8_t id, uint64_t packet_num, uint32_t normal, uint32_t zero, uint32_t flags, uint32_t next_packet_size) "channel %u packet_num %" PRIu64 " normal pages %u zero pages %u flags 0x%x next packet size %u"
 multifd_recv_new_channel(uint8_t id) "channel %u"
 multifd_recv_sync_main(long packet_num) "packet num %ld"
 multifd_recv_sync_main_signal(uint8_t id) "channel %u"
 multifd_recv_sync_main_wait(uint8_t id) "channel %u"
 multifd_recv_terminate_threads(bool error) "error %d"
-multifd_recv_thread_end(uint8_t id, uint64_t packets, uint64_t pages) "channel %u packets %" PRIu64 " pages %" PRIu64
+multifd_recv_thread_end(uint8_t id, uint64_t packets, uint64_t normal_pages, uint64_t zero_pages) "channel %u packets %" PRIu64 " normal pages %" PRIu64 " zero pages %" PRIu64
 multifd_recv_thread_start(uint8_t id) "%u"
-multifd_send(uint8_t id, uint64_t packet_num, uint32_t normal, uint32_t flags, uint32_t next_packet_size) "channel %u packet_num %" PRIu64 " normal pages %u flags 0x%x next packet size %u"
+multifd_send(uint8_t id, uint64_t packet_num, uint32_t normalpages, uint32_t zero_pages, uint32_t flags, uint32_t next_packet_size) "channel %u packet_num %" PRIu64 " normal pages %u zero pages %u flags 0x%x next packet size %u"
 multifd_send_error(uint8_t id) "channel %u"
 multifd_send_sync_main(long packet_num) "packet num %ld"
 multifd_send_sync_main_signal(uint8_t id) "channel %u"
 multifd_send_sync_main_wait(uint8_t id) "channel %u"
 multifd_send_terminate_threads(bool error) "error %d"
-multifd_send_thread_end(uint8_t id, uint64_t packets, uint64_t normal_pages) "channel %u packets %" PRIu64 " normal pages %"  PRIu64
+multifd_send_thread_end(uint8_t id, uint64_t packets, uint64_t normal_pages, uint64_t zero_pages) "channel %u packets %" PRIu64 " normal pages %"  PRIu64 " zero pages %"  PRIu64
 multifd_send_thread_start(uint8_t id) "%u"
 multifd_tls_outgoing_handshake_start(void *ioc, void *tioc, const char *hostname) "ioc=%p tioc=%p hostname=%s"
 multifd_tls_outgoing_handshake_error(void *ioc, const char *err) "ioc=%p err=%s"
-- 
2.38.1

[PATCH 10/11] multifd: Zero pages transmission

[Juan Quintela]

This implements the zero page dection and handling.

Signed-off-by: Juan Quintela <quintela@redhat.com>

---

Add comment for offset (dave)
Use local variables for offset/block to have shorter lines
---
 migration/multifd.h |  5 +++++
 migration/multifd.c | 45 +++++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 48 insertions(+), 2 deletions(-)

diff --git a/migration/multifd.h b/migration/multifd.h
index a1b852200d..5931de6f86 100644
--- a/migration/multifd.h
+++ b/migration/multifd.h
@@ -52,6 +52,11 @@ typedef struct {
     uint32_t unused32[1];    /* Reserved for future use */
     uint64_t unused64[3];    /* Reserved for future use */
     char ramblock[256];
+    /*
+     * This array contains the pointers to:
+     *  - normal pages (initial normal_pages entries)
+     *  - zero pages (following zero_pages entries)
+     */
     uint64_t offset[];
 } __attribute__((packed)) MultiFDPacket_t;
 
diff --git a/migration/multifd.c b/migration/multifd.c
index 30cc206190..d3f82dad8a 100644
--- a/migration/multifd.c
+++ b/migration/multifd.c
@@ -11,6 +11,7 @@
  */
 
 #include "qemu/osdep.h"
+#include "qemu/cutils.h"
 #include "qemu/rcu.h"
 #include "exec/target_page.h"
 #include "sysemu/sysemu.h"
@@ -275,6 +276,12 @@ static void multifd_send_fill_packet(MultiFDSendParams *p)
 
         packet->offset[i] = cpu_to_be64(temp);
     }
+    for (i = 0; i < p->zero_num; i++) {
+        /* there are architectures where ram_addr_t is 32 bit */
+        uint64_t temp = p->zero[i];
+
+        packet->offset[p->normal_num + i] = cpu_to_be64(temp);
+    }
 }
 
 static int multifd_recv_unfill_packet(MultiFDRecvParams *p, Error **errp)
@@ -358,6 +365,18 @@ static int multifd_recv_unfill_packet(MultiFDRecvParams *p, Error **errp)
         p->normal[i] = offset;
     }
 
+    for (i = 0; i < p->zero_num; i++) {
+        uint64_t offset = be64_to_cpu(packet->offset[p->normal_num + i]);
+
+        if (offset > (block->used_length - p->page_size)) {
+            error_setg(errp, "multifd: offset too long %" PRIu64
+                       " (max " RAM_ADDR_FMT ")",
+                       offset, block->used_length);
+            return -1;
+        }
+        p->zero[i] = offset;
+    }
+
     return 0;
 }
 
@@ -657,6 +676,12 @@ static void *multifd_send_thread(void *opaque)
 {
     MultiFDSendParams *p = opaque;
     Error *local_err = NULL;
+    /*
+     * older qemu don't understand zero page on multifd channel.  To
+     * have capabilities "false" by default, we need to name it this
+     * way.
+     */
+    bool use_multifd_zero_page = !migrate_use_main_zero_page();
     int ret = 0;
     bool use_zero_copy_send = migrate_use_zero_copy_send();
 
@@ -679,6 +704,7 @@ static void *multifd_send_thread(void *opaque)
         qemu_mutex_lock(&p->mutex);
 
         if (p->pending_job) {
+            RAMBlock *rb = p->pages->block;
             uint64_t packet_num = p->packet_num;
             p->flags = 0;
             if (p->sync_needed) {
@@ -697,8 +723,16 @@ static void *multifd_send_thread(void *opaque)
             }
 
             for (int i = 0; i < p->pages->num; i++) {
-                p->normal[p->normal_num] = p->pages->offset[i];
-                p->normal_num++;
+                uint64_t offset = p->pages->offset[i];
+                if (use_multifd_zero_page &&
+                    buffer_is_zero(rb->host + offset, p->page_size)) {
+                    p->zero[p->zero_num] = offset;
+                    p->zero_num++;
+                    ram_release_page(rb->idstr, offset);
+                } else {
+                    p->normal[p->normal_num] = offset;
+                    p->normal_num++;
+                }
             }
 
             if (p->normal_num) {
@@ -1160,6 +1194,13 @@ static void *multifd_recv_thread(void *opaque)
             }
         }
 
+        for (int i = 0; i < p->zero_num; i++) {
+            void *page = p->host + p->zero[i];
+            if (!buffer_is_zero(page, p->page_size)) {
+                memset(page, 0, p->page_size);
+            }
+        }
+
         if (sync_needed) {
             qemu_sem_post(&multifd_recv_state->sem_sync);
             qemu_sem_wait(&p->sem_sync);
-- 
2.38.1

[PATCH 11/11] So we use multifd to transmit zero pages.

[Juan Quintela]

Signed-off-by: Juan Quintela <quintela@redhat.com>

---

- Check zero_page property before using new code (Dave)
---
 migration/migration.c |  3 +--
 migration/ram.c       | 32 +++++++++++++++++++++++++++++++-
 2 files changed, 32 insertions(+), 3 deletions(-)

diff --git a/migration/migration.c b/migration/migration.c
index 2a828764ed..1cdeeb19b8 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -2616,8 +2616,7 @@ bool migrate_use_main_zero_page(void)
 {
     MigrationState *s = migrate_get_current();
 
-    /* We will enable this when we add the right code. */
-    return true || s->enabled_capabilities[MIGRATION_CAPABILITY_MAIN_ZERO_PAGE];
+    return s->enabled_capabilities[MIGRATION_CAPABILITY_MAIN_ZERO_PAGE];
 }
 
 bool migrate_pause_before_switchover(void)
diff --git a/migration/ram.c b/migration/ram.c
index f23a01719b..f14ee63728 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -2404,6 +2404,31 @@ out:
     return ret;
 }
 
+/**
+ * ram_save_target_page_multifd: save one target page
+ *
+ * Returns the number of pages written
+ *
+ * @rs: current RAM state
+ * @pss: data about the page we want to send
+ */
+static int ram_save_target_page_multifd(RAMState *rs, PageSearchStatus *pss)
+{
+    RAMBlock *block = pss->block;
+    ram_addr_t offset = ((ram_addr_t)pss->page) << TARGET_PAGE_BITS;
+
+    if (!migration_in_postcopy()) {
+        return ram_save_multifd_page(pss->pss_channel, block, offset);
+    }
+
+    int res = save_zero_page(pss, block, offset);
+    if (res > 0) {
+        return res;
+    }
+
+    return ram_save_page(rs, pss);
+}
+
 /**
  * ram_save_host_page: save a whole host page
  *
@@ -3206,7 +3231,12 @@ static int ram_save_setup(QEMUFile *f, void *opaque)
     ram_control_after_iterate(f, RAM_CONTROL_SETUP);
 
     migration_ops = g_malloc0(sizeof(MigrationOps));
-    migration_ops->ram_save_target_page = ram_save_target_page_legacy;
+    if (migrate_use_multifd() && !migrate_use_main_zero_page()) {
+        migration_ops->ram_save_target_page = ram_save_target_page_multifd;
+    } else {
+        migration_ops->ram_save_target_page = ram_save_target_page_legacy;
+    }
+
     ret =  multifd_send_sync_main(f);
     if (ret < 0) {
         return ret;
-- 
2.38.1