migration/multifd: solve zero page causing multiple page faults
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>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20240401154110.2028453-2-yuan1.liu@intel.com
[peterx: touch up the comment, as the bitmap is used outside postcopy now]
Signed-off-by: Peter Xu <peterx@redhat.com>
diff --git a/include/exec/ramblock.h b/include/exec/ramblock.h
index 848915e..7062da3 100644
--- a/include/exec/ramblock.h
+++ b/include/exec/ramblock.h
@@ -57,7 +57,7 @@
off_t bitmap_offset;
uint64_t pages_offset;
- /* bitmap of already received pages in postcopy */
+ /* Bitmap of already received pages. Only used on destination side. */
unsigned long *receivedmap;
/*
diff --git a/migration/multifd-zero-page.c b/migration/multifd-zero-page.c
index 1ba38be..e1b8370 100644
--- a/migration/multifd-zero-page.c
+++ b/migration/multifd-zero-page.c
@@ -80,8 +80,10 @@
{
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 99821cd..737a964 100644
--- a/migration/multifd-zlib.c
+++ b/migration/multifd-zlib.c
@@ -284,6 +284,7 @@
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 0211225..256858d 100644
--- a/migration/multifd-zstd.c
+++ b/migration/multifd-zstd.c
@@ -278,6 +278,7 @@
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 2802afe..f317bff 100644
--- a/migration/multifd.c
+++ b/migration/multifd.c
@@ -277,6 +277,7 @@
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 daffcd8..a975c5a 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -275,6 +275,10 @@
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 08feeca..bc0318b 100644
--- a/migration/ram.h
+++ b/migration/ram.h
@@ -69,6 +69,7 @@
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);
