[PATCH 1/1] migration/multifd: solve zero page causing multiple page faults

[Yuan Liu <yuan1.liu@intel.com>]

Implemented recvbitmap tracking of received pages in multifd.

If the zero page appears for the first time in the recvbitmap, this
page is not checked and set.

If the zero page has already appeared in the recvbitmap, there is no
need to check the data but directly set the data to 0, because it is
unlikely that the zero page will be migrated multiple times.

Signed-off-by: Yuan Liu <yuan1.liu@intel.com>
---
 migration/multifd-zero-page.c | 4 +++-
 migration/multifd-zlib.c      | 1 +
 migration/multifd-zstd.c      | 1 +
 migration/multifd.c           | 1 +
 migration/ram.c               | 4 ++++
 migration/ram.h               | 1 +
 6 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/migration/multifd-zero-page.c b/migration/multifd-zero-page.c
index 1ba38be636..e1b8370f88 100644
--- a/migration/multifd-zero-page.c
+++ b/migration/multifd-zero-page.c
@@ -80,8 +80,10 @@ void multifd_recv_zero_page_process(MultiFDRecvParams *p)
 {
     for (int i = 0; i < p->zero_num; i++) {
         void *page = p->host + p->zero[i];
-        if (!buffer_is_zero(page, p->page_size)) {
+        if (ramblock_recv_bitmap_test_byte_offset(p->block, p->zero[i])) {
             memset(page, 0, p->page_size);
+        } else {
+            ramblock_recv_bitmap_set_offset(p->block, p->zero[i]);
         }
     }
 }
diff --git a/migration/multifd-zlib.c b/migration/multifd-zlib.c
index 8095ef8e28..6246ecca2b 100644
--- a/migration/multifd-zlib.c
+++ b/migration/multifd-zlib.c
@@ -288,6 +288,7 @@ static int zlib_recv(MultiFDRecvParams *p, Error **errp)
         int flush = Z_NO_FLUSH;
         unsigned long start = zs->total_out;
 
+        ramblock_recv_bitmap_set_offset(p->block, p->normal[i]);
         if (i == p->normal_num - 1) {
             flush = Z_SYNC_FLUSH;
         }
diff --git a/migration/multifd-zstd.c b/migration/multifd-zstd.c
index 9c9217794e..989333b572 100644
--- a/migration/multifd-zstd.c
+++ b/migration/multifd-zstd.c
@@ -282,6 +282,7 @@ static int zstd_recv(MultiFDRecvParams *p, Error **errp)
     z->in.pos = 0;
 
     for (i = 0; i < p->normal_num; i++) {
+        ramblock_recv_bitmap_set_offset(p->block, p->normal[i]);
         z->out.dst = p->host + p->normal[i];
         z->out.size = p->page_size;
         z->out.pos = 0;
diff --git a/migration/multifd.c b/migration/multifd.c
index 72712fc31f..c9f544dba0 100644
--- a/migration/multifd.c
+++ b/migration/multifd.c
@@ -277,6 +277,7 @@ static int nocomp_recv(MultiFDRecvParams *p, Error **errp)
     for (int i = 0; i < p->normal_num; i++) {
         p->iov[i].iov_base = p->host + p->normal[i];
         p->iov[i].iov_len = p->page_size;
+        ramblock_recv_bitmap_set_offset(p->block, p->normal[i]);
     }
     return qio_channel_readv_all(p->c, p->iov, p->normal_num, errp);
 }
diff --git a/migration/ram.c b/migration/ram.c
index 8deb84984f..3aa70794c1 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -275,6 +275,10 @@ void ramblock_recv_bitmap_set_range(RAMBlock *rb, void *host_addr,
                       nr);
 }
 
+void ramblock_recv_bitmap_set_offset(RAMBlock *rb, uint64_t byte_offset)
+{
+    set_bit_atomic(byte_offset >> TARGET_PAGE_BITS, rb->receivedmap);
+}
 #define  RAMBLOCK_RECV_BITMAP_ENDING  (0x0123456789abcdefULL)
 
 /*
diff --git a/migration/ram.h b/migration/ram.h
index 08feecaf51..bc0318b834 100644
--- a/migration/ram.h
+++ b/migration/ram.h
@@ -69,6 +69,7 @@ int ramblock_recv_bitmap_test(RAMBlock *rb, void *host_addr);
 bool ramblock_recv_bitmap_test_byte_offset(RAMBlock *rb, uint64_t byte_offset);
 void ramblock_recv_bitmap_set(RAMBlock *rb, void *host_addr);
 void ramblock_recv_bitmap_set_range(RAMBlock *rb, void *host_addr, size_t nr);
+void ramblock_recv_bitmap_set_offset(RAMBlock *rb, uint64_t byte_offset);
 int64_t ramblock_recv_bitmap_send(QEMUFile *file,
                                   const char *block_name);
 bool ram_dirty_bitmap_reload(MigrationState *s, RAMBlock *rb, Error **errp);
-- 
2.39.3