Re: [PATCH v2 03/20] multifd: Zero pages transmission

[Wang, Lei]

On 11/14/2023 13:40, Hao Xiang wrote:> From: Juan Quintela 
> 
> This implements the zero page dection and handling.

s/dection/detection

> 
> Signed-off-by: Juan Quintela 
> ---
>  migration/multifd.c | 41 +++--
>  migration/multifd.h |  5 +

[...]

> +/*
> + * This array contains the pointers to:

it contains the offsets in the RAMBlock, not the real pointer.

> + *  - normal pages (initial normal_pages entries)
> + *  - zero pages (following zero_pages entries)
> + */
>  uint64_t offset[];
>  } __attribute__((packed)) MultiFDPacket_t;
>  

[PATCH v2 03/20] multifd: Zero pages transmission

[Hao Xiang]

From: Juan Quintela 

This implements the zero page dection and handling.

Signed-off-by: Juan Quintela 
---
 migration/multifd.c | 41 +++--
 migration/multifd.h |  5 +
 2 files changed, 44 insertions(+), 2 deletions(-)

diff --git a/migration/multifd.c b/migration/multifd.c
index d28ef0028b..1b994790d5 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"
@@ -279,6 +280,12 @@ 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)
@@ -361,6 +368,18 @@ 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 > (p->block->used_length - p->page_size)) {
+error_setg(errp, "multifd: offset too long %" PRIu64
+   " (max " RAM_ADDR_FMT ")",
+   offset, p->block->used_length);
+return -1;
+}
+p->zero[i] = offset;
+}
+
 return 0;
 }
 
@@ -664,6 +683,8 @@ static void *multifd_send_thread(void *opaque)
 MultiFDSendParams *p = opaque;
 MigrationThread *thread = NULL;
 Error *local_err = NULL;
+/* qemu older than 8.2 don't understand zero page on multifd channel */
+bool use_zero_page = !migrate_use_main_zero_page();
 int ret = 0;
 bool use_zero_copy_send = migrate_zero_copy_send();
 
@@ -689,6 +710,7 @@ static void *multifd_send_thread(void *opaque)
 qemu_mutex_lock(>mutex);
 
 if (p->pending_job) {
+RAMBlock *rb = p->pages->block;
 uint64_t packet_num = p->packet_num;
 uint32_t flags;
 p->normal_num = 0;
@@ -701,8 +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_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) {
@@ -1156,6 +1186,13 @@ 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 (flags & MULTIFD_FLAG_SYNC) {
 qemu_sem_post(_recv_state->sem_sync);
 qemu_sem_wait(>sem_sync);
diff --git a/migration/multifd.h b/migration/multifd.h
index d587b0e19c..13762900d4 100644
--- a/migration/multifd.h
+++ b/migration/multifd.h
@@ -53,6 +53,11 @@ 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;
 
-- 
2.30.2