diff mbox series

[V7,RESEND,07/17] COLO: Load dirty pages into SVM's RAM cache firstly

Message ID 20180514165424.12884-8-zhangckid@gmail.com
State New
Headers show
Series COLO: integrate colo frame with block replication and COLO proxy | expand

Commit Message

Zhang Chen May 14, 2018, 4:54 p.m. UTC 
We should not load PVM's state directly into SVM, because there maybe some
errors happen when SVM is receving data, which will break SVM.

We need to ensure receving all data before load the state into SVM. We use
an extra memory to cache these data (PVM's ram). The ram cache in secondary side
is initially the same as SVM/PVM's memory. And in the process of checkpoint,
we cache the dirty pages of PVM into this ram cache firstly, so this ram cache
always the same as PVM's memory at every checkpoint, then we flush this cached ram
to SVM after we receive all PVM's state.

Signed-off-by: zhanghailiang <zhang.zhanghailiang@huawei.com>
Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>
Signed-off-by: Zhang Chen <zhangckid@gmail.com>
---
 include/exec/ram_addr.h |  1 +
 migration/migration.c   |  2 +
 migration/ram.c         | 99 +++++++++++++++++++++++++++++++++++++++--
 migration/ram.h         |  4 ++
 migration/savevm.c      |  2 +-
 5 files changed, 104 insertions(+), 4 deletions(-)

Comments

Dr. David Alan Gilbert May 15, 2018, 4:55 p.m. UTC | #1 
* Zhang Chen (zhangckid@gmail.com) wrote:
> We should not load PVM's state directly into SVM, because there maybe some
> errors happen when SVM is receving data, which will break SVM.
> 
> We need to ensure receving all data before load the state into SVM. We use
> an extra memory to cache these data (PVM's ram). The ram cache in secondary side
> is initially the same as SVM/PVM's memory. And in the process of checkpoint,
> we cache the dirty pages of PVM into this ram cache firstly, so this ram cache
> always the same as PVM's memory at every checkpoint, then we flush this cached ram
> to SVM after we receive all PVM's state.
> 
> Signed-off-by: zhanghailiang <zhang.zhanghailiang@huawei.com>
> Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>
> Signed-off-by: Zhang Chen <zhangckid@gmail.com>
> ---
>  include/exec/ram_addr.h |  1 +
>  migration/migration.c   |  2 +
>  migration/ram.c         | 99 +++++++++++++++++++++++++++++++++++++++--
>  migration/ram.h         |  4 ++
>  migration/savevm.c      |  2 +-
>  5 files changed, 104 insertions(+), 4 deletions(-)
> 
> diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
> index cf2446a176..51ec153a57 100644
> --- a/include/exec/ram_addr.h
> +++ b/include/exec/ram_addr.h
> @@ -27,6 +27,7 @@ struct RAMBlock {
>      struct rcu_head rcu;
>      struct MemoryRegion *mr;
>      uint8_t *host;
> +    uint8_t *colo_cache; /* For colo, VM's ram cache */
>      ram_addr_t offset;
>      ram_addr_t used_length;
>      ram_addr_t max_length;
> diff --git a/migration/migration.c b/migration/migration.c
> index 8dee7dd309..cfc1b958b9 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -421,6 +421,8 @@ static void process_incoming_migration_co(void *opaque)
>  
>          /* Wait checkpoint incoming thread exit before free resource */
>          qemu_thread_join(&mis->colo_incoming_thread);
> +        /* We hold the global iothread lock, so it is safe here */
> +        colo_release_ram_cache();
>      }
>  
>      if (ret < 0) {
> diff --git a/migration/ram.c b/migration/ram.c
> index 912810c18e..7ca845f8a9 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -2520,6 +2520,20 @@ static inline void *host_from_ram_block_offset(RAMBlock *block,
>      return block->host + offset;
>  }
>  
> +static inline void *colo_cache_from_block_offset(RAMBlock *block,
> +                                                 ram_addr_t offset)
> +{
> +    if (!offset_in_ramblock(block, offset)) {
> +        return NULL;
> +    }
> +    if (!block->colo_cache) {
> +        error_report("%s: colo_cache is NULL in block :%s",
> +                     __func__, block->idstr);
> +        return NULL;
> +    }
> +    return block->colo_cache + offset;
> +}
> +
>  /**
>   * ram_handle_compressed: handle the zero page case
>   *
> @@ -2724,6 +2738,57 @@ static void decompress_data_with_multi_threads(QEMUFile *f,
>      qemu_mutex_unlock(&decomp_done_lock);
>  }
>  
> +/*
> + * colo cache: this is for secondary VM, we cache the whole
> + * memory of the secondary VM, it is need to hold the global lock
> + * to call this helper.
> + */
> +int colo_init_ram_cache(void)
> +{
> +    RAMBlock *block;
> +
> +    rcu_read_lock();
> +    QLIST_FOREACH_RCU(block, &ram_list.blocks, next) {
> +        block->colo_cache = qemu_anon_ram_alloc(block->used_length,
> +                                                NULL,
> +                                                false);
> +        if (!block->colo_cache) {
> +            error_report("%s: Can't alloc memory for COLO cache of block %s,"
> +                         "size 0x" RAM_ADDR_FMT, __func__, block->idstr,
> +                         block->used_length);
> +            goto out_locked;
> +        }
> +    }
> +    rcu_read_unlock();
> +    return 0;
> +
> +out_locked:
> +    QLIST_FOREACH_RCU(block, &ram_list.blocks, next) {
> +        if (block->colo_cache) {
> +            qemu_anon_ram_free(block->colo_cache, block->used_length);
> +            block->colo_cache = NULL;
> +        }
> +    }
> +
> +    rcu_read_unlock();
> +    return -errno;
> +}
> +
> +/* It is need to hold the global lock to call this helper */
> +void colo_release_ram_cache(void)
> +{
> +    RAMBlock *block;
> +
> +    rcu_read_lock();
> +    QLIST_FOREACH_RCU(block, &ram_list.blocks, next) {
> +        if (block->colo_cache) {
> +            qemu_anon_ram_free(block->colo_cache, block->used_length);
> +            block->colo_cache = NULL;
> +        }
> +    }
> +    rcu_read_unlock();
> +}
> +
>  /**
>   * ram_load_setup: Setup RAM for migration incoming side
>   *
> @@ -2740,6 +2805,7 @@ static int ram_load_setup(QEMUFile *f, void *opaque)
>  
>      xbzrle_load_setup();
>      ramblock_recv_map_init();
> +
>      return 0;
>  }
>  
> @@ -2753,6 +2819,7 @@ static int ram_load_cleanup(void *opaque)
>          g_free(rb->receivedmap);
>          rb->receivedmap = NULL;
>      }
> +
>      return 0;
>  }
>  
> @@ -2966,7 +3033,7 @@ static int ram_load(QEMUFile *f, void *opaque, int version_id)
>  
>      while (!postcopy_running && !ret && !(flags & RAM_SAVE_FLAG_EOS)) {
>          ram_addr_t addr, total_ram_bytes;
> -        void *host = NULL;
> +        void *host = NULL, *host_bak = NULL;
>          uint8_t ch;
>  
>          addr = qemu_get_be64(f);
> @@ -2986,13 +3053,36 @@ static int ram_load(QEMUFile *f, void *opaque, int version_id)
>                       RAM_SAVE_FLAG_COMPRESS_PAGE | RAM_SAVE_FLAG_XBZRLE)) {
>              RAMBlock *block = ram_block_from_stream(f, flags);
>  
> -            host = host_from_ram_block_offset(block, addr);
> +             /*
> +             * After going into COLO, we should load the Page into colo_cache
> +             * NOTE: We need to keep a copy of SVM's ram in colo_cache.
> +             * Privously, we copied all these memory in preparing stage of COLO
> +             * while we need to stop VM, which is a time-consuming process.
> +             * Here we optimize it by a trick, back-up every page while in
> +             * migration process while COLO is enabled, though it affects the
> +             * speed of the migration, but it obviously reduce the downtime of
> +             * back-up all SVM'S memory in COLO preparing stage.
> +             */
> +            if (migration_incoming_in_colo_state()) {
> +                host = colo_cache_from_block_offset(block, addr);
> +                /* After goes into COLO state, don't backup it any more */
> +                if (!migration_incoming_in_colo_state()) {

I don't understand how we can reach this nested 'if';
colo_cache_from_block_offset is short and simple; so how can
migration_incoming_in_colo_state() be both true and false?

I think this is trying to do it for when COLO is enabled but when
receiving the first checkpoint you want to take a copy; but I don't
think that's what the 'if' is doing.

Dave

> +                    host_bak = host;
> +                }
> +            }
> +            if (!migration_incoming_in_colo_state()) {
> +                host = host_from_ram_block_offset(block, addr);
> +            }
>              if (!host) {
>                  error_report("Illegal RAM offset " RAM_ADDR_FMT, addr);
>                  ret = -EINVAL;
>                  break;
>              }
> -            ramblock_recv_bitmap_set(block, host);
> +
> +            if (!migration_incoming_in_colo_state()) {
> +                ramblock_recv_bitmap_set(block, host);
> +            }
> +
>              trace_ram_load_loop(block->idstr, (uint64_t)addr, flags, host);
>          }
>  
> @@ -3087,6 +3177,9 @@ static int ram_load(QEMUFile *f, void *opaque, int version_id)
>          if (!ret) {
>              ret = qemu_file_get_error(f);
>          }
> +        if (!ret && host_bak && host) {
> +            memcpy(host_bak, host, TARGET_PAGE_SIZE);
> +        }
>      }
>  
>      ret |= wait_for_decompress_done();
> diff --git a/migration/ram.h b/migration/ram.h
> index 5030be110a..66e9b86ff0 100644
> --- a/migration/ram.h
> +++ b/migration/ram.h
> @@ -64,4 +64,8 @@ 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);
>  
> +/* ram cache */
> +int colo_init_ram_cache(void);
> +void colo_release_ram_cache(void);
> +
>  #endif
> diff --git a/migration/savevm.c b/migration/savevm.c
> index c43d220220..ec0bff09ce 100644
> --- a/migration/savevm.c
> +++ b/migration/savevm.c
> @@ -1807,7 +1807,7 @@ static int loadvm_handle_cmd_packaged(MigrationIncomingState *mis)
>  static int loadvm_process_enable_colo(MigrationIncomingState *mis)
>  {
>      migration_incoming_enable_colo();
> -    return 0;
> +    return colo_init_ram_cache();
>  }
>  
>  /*
> -- 
> 2.17.0
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
Zhang Chen May 20, 2018, 6:30 p.m. UTC | #2 
On Wed, May 16, 2018 at 12:55 AM, Dr. David Alan Gilbert <
dgilbert@redhat.com> wrote:

> * Zhang Chen (zhangckid@gmail.com) wrote:
> > We should not load PVM's state directly into SVM, because there maybe
> some
> > errors happen when SVM is receving data, which will break SVM.
> >
> > We need to ensure receving all data before load the state into SVM. We
> use
> > an extra memory to cache these data (PVM's ram). The ram cache in
> secondary side
> > is initially the same as SVM/PVM's memory. And in the process of
> checkpoint,
> > we cache the dirty pages of PVM into this ram cache firstly, so this ram
> cache
> > always the same as PVM's memory at every checkpoint, then we flush this
> cached ram
> > to SVM after we receive all PVM's state.
> >
> > Signed-off-by: zhanghailiang <zhang.zhanghailiang@huawei.com>
> > Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>
> > Signed-off-by: Zhang Chen <zhangckid@gmail.com>
> > ---
> >  include/exec/ram_addr.h |  1 +
> >  migration/migration.c   |  2 +
> >  migration/ram.c         | 99 +++++++++++++++++++++++++++++++++++++++--
> >  migration/ram.h         |  4 ++
> >  migration/savevm.c      |  2 +-
> >  5 files changed, 104 insertions(+), 4 deletions(-)
> >
> > diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
> > index cf2446a176..51ec153a57 100644
> > --- a/include/exec/ram_addr.h
> > +++ b/include/exec/ram_addr.h
> > @@ -27,6 +27,7 @@ struct RAMBlock {
> >      struct rcu_head rcu;
> >      struct MemoryRegion *mr;
> >      uint8_t *host;
> > +    uint8_t *colo_cache; /* For colo, VM's ram cache */
> >      ram_addr_t offset;
> >      ram_addr_t used_length;
> >      ram_addr_t max_length;
> > diff --git a/migration/migration.c b/migration/migration.c
> > index 8dee7dd309..cfc1b958b9 100644
> > --- a/migration/migration.c
> > +++ b/migration/migration.c
> > @@ -421,6 +421,8 @@ static void process_incoming_migration_co(void
> *opaque)
> >
> >          /* Wait checkpoint incoming thread exit before free resource */
> >          qemu_thread_join(&mis->colo_incoming_thread);
> > +        /* We hold the global iothread lock, so it is safe here */
> > +        colo_release_ram_cache();
> >      }
> >
> >      if (ret < 0) {
> > diff --git a/migration/ram.c b/migration/ram.c
> > index 912810c18e..7ca845f8a9 100644
> > --- a/migration/ram.c
> > +++ b/migration/ram.c
> > @@ -2520,6 +2520,20 @@ static inline void *host_from_ram_block_offset(RAMBlock
> *block,
> >      return block->host + offset;
> >  }
> >
> > +static inline void *colo_cache_from_block_offset(RAMBlock *block,
> > +                                                 ram_addr_t offset)
> > +{
> > +    if (!offset_in_ramblock(block, offset)) {
> > +        return NULL;
> > +    }
> > +    if (!block->colo_cache) {
> > +        error_report("%s: colo_cache is NULL in block :%s",
> > +                     __func__, block->idstr);
> > +        return NULL;
> > +    }
> > +    return block->colo_cache + offset;
> > +}
> > +
> >  /**
> >   * ram_handle_compressed: handle the zero page case
> >   *
> > @@ -2724,6 +2738,57 @@ static void decompress_data_with_multi_threads(QEMUFile
> *f,
> >      qemu_mutex_unlock(&decomp_done_lock);
> >  }
> >
> > +/*
> > + * colo cache: this is for secondary VM, we cache the whole
> > + * memory of the secondary VM, it is need to hold the global lock
> > + * to call this helper.
> > + */
> > +int colo_init_ram_cache(void)
> > +{
> > +    RAMBlock *block;
> > +
> > +    rcu_read_lock();
> > +    QLIST_FOREACH_RCU(block, &ram_list.blocks, next) {
> > +        block->colo_cache = qemu_anon_ram_alloc(block->used_length,
> > +                                                NULL,
> > +                                                false);
> > +        if (!block->colo_cache) {
> > +            error_report("%s: Can't alloc memory for COLO cache of
> block %s,"
> > +                         "size 0x" RAM_ADDR_FMT, __func__, block->idstr,
> > +                         block->used_length);
> > +            goto out_locked;
> > +        }
> > +    }
> > +    rcu_read_unlock();
> > +    return 0;
> > +
> > +out_locked:
> > +    QLIST_FOREACH_RCU(block, &ram_list.blocks, next) {
> > +        if (block->colo_cache) {
> > +            qemu_anon_ram_free(block->colo_cache, block->used_length);
> > +            block->colo_cache = NULL;
> > +        }
> > +    }
> > +
> > +    rcu_read_unlock();
> > +    return -errno;
> > +}
> > +
> > +/* It is need to hold the global lock to call this helper */
> > +void colo_release_ram_cache(void)
> > +{
> > +    RAMBlock *block;
> > +
> > +    rcu_read_lock();
> > +    QLIST_FOREACH_RCU(block, &ram_list.blocks, next) {
> > +        if (block->colo_cache) {
> > +            qemu_anon_ram_free(block->colo_cache, block->used_length);
> > +            block->colo_cache = NULL;
> > +        }
> > +    }
> > +    rcu_read_unlock();
> > +}
> > +
> >  /**
> >   * ram_load_setup: Setup RAM for migration incoming side
> >   *
> > @@ -2740,6 +2805,7 @@ static int ram_load_setup(QEMUFile *f, void
> *opaque)
> >
> >      xbzrle_load_setup();
> >      ramblock_recv_map_init();
> > +
> >      return 0;
> >  }
> >
> > @@ -2753,6 +2819,7 @@ static int ram_load_cleanup(void *opaque)
> >          g_free(rb->receivedmap);
> >          rb->receivedmap = NULL;
> >      }
> > +
> >      return 0;
> >  }
> >
> > @@ -2966,7 +3033,7 @@ static int ram_load(QEMUFile *f, void *opaque, int
> version_id)
> >
> >      while (!postcopy_running && !ret && !(flags & RAM_SAVE_FLAG_EOS)) {
> >          ram_addr_t addr, total_ram_bytes;
> > -        void *host = NULL;
> > +        void *host = NULL, *host_bak = NULL;
> >          uint8_t ch;
> >
> >          addr = qemu_get_be64(f);
> > @@ -2986,13 +3053,36 @@ static int ram_load(QEMUFile *f, void *opaque,
> int version_id)
> >                       RAM_SAVE_FLAG_COMPRESS_PAGE |
> RAM_SAVE_FLAG_XBZRLE)) {
> >              RAMBlock *block = ram_block_from_stream(f, flags);
> >
> > -            host = host_from_ram_block_offset(block, addr);
> > +             /*
> > +             * After going into COLO, we should load the Page into
> colo_cache
> > +             * NOTE: We need to keep a copy of SVM's ram in colo_cache.
> > +             * Privously, we copied all these memory in preparing stage
> of COLO
> > +             * while we need to stop VM, which is a time-consuming
> process.
> > +             * Here we optimize it by a trick, back-up every page while
> in
> > +             * migration process while COLO is enabled, though it
> affects the
> > +             * speed of the migration, but it obviously reduce the
> downtime of
> > +             * back-up all SVM'S memory in COLO preparing stage.
> > +             */
> > +            if (migration_incoming_in_colo_state()) {
> > +                host = colo_cache_from_block_offset(block, addr);
> > +                /* After goes into COLO state, don't backup it any more
> */
> > +                if (!migration_incoming_in_colo_state()) {
>
> I don't understand how we can reach this nested 'if';
> colo_cache_from_block_offset is short and simple; so how can
> migration_incoming_in_colo_state() be both true and false?
>
> I think this is trying to do it for when COLO is enabled but when
> receiving the first checkpoint you want to take a copy; but I don't
> think that's what the 'if' is doing.
>

I'm also confused about this part.
I checked old version codes for this part, but it looks same .
How do you think this should be done?

Or maybe the original author know some detail?
CC Lizhijian and Zhanghailiang

Thanks
Zhang Chen




>
> Dave
>
> > +                    host_bak = host;
> > +                }
> > +            }
> > +            if (!migration_incoming_in_colo_state()) {
> > +                host = host_from_ram_block_offset(block, addr);
> > +            }
> >              if (!host) {
> >                  error_report("Illegal RAM offset " RAM_ADDR_FMT, addr);
> >                  ret = -EINVAL;
> >                  break;
> >              }
> > -            ramblock_recv_bitmap_set(block, host);
> > +
> > +            if (!migration_incoming_in_colo_state()) {
> > +                ramblock_recv_bitmap_set(block, host);
> > +            }
> > +
> >              trace_ram_load_loop(block->idstr, (uint64_t)addr, flags,
> host);
> >          }
> >
> > @@ -3087,6 +3177,9 @@ static int ram_load(QEMUFile *f, void *opaque, int
> version_id)
> >          if (!ret) {
> >              ret = qemu_file_get_error(f);
> >          }
> > +        if (!ret && host_bak && host) {
> > +            memcpy(host_bak, host, TARGET_PAGE_SIZE);
> > +        }
> >      }
> >
> >      ret |= wait_for_decompress_done();
> > diff --git a/migration/ram.h b/migration/ram.h
> > index 5030be110a..66e9b86ff0 100644
> > --- a/migration/ram.h
> > +++ b/migration/ram.h
> > @@ -64,4 +64,8 @@ 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);
> >
> > +/* ram cache */
> > +int colo_init_ram_cache(void);
> > +void colo_release_ram_cache(void);
> > +
> >  #endif
> > diff --git a/migration/savevm.c b/migration/savevm.c
> > index c43d220220..ec0bff09ce 100644
> > --- a/migration/savevm.c
> > +++ b/migration/savevm.c
> > @@ -1807,7 +1807,7 @@ static int loadvm_handle_cmd_packaged(MigrationIncomingState
> *mis)
> >  static int loadvm_process_enable_colo(MigrationIncomingState *mis)
> >  {
> >      migration_incoming_enable_colo();
> > -    return 0;
> > +    return colo_init_ram_cache();
> >  }
> >
> >  /*
> > --
> > 2.17.0
> >
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
>
diff mbox series

Patch

diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
index cf2446a176..51ec153a57 100644
--- a/include/exec/ram_addr.h
+++ b/include/exec/ram_addr.h
@@ -27,6 +27,7 @@  struct RAMBlock {
     struct rcu_head rcu;
     struct MemoryRegion *mr;
     uint8_t *host;
+    uint8_t *colo_cache; /* For colo, VM's ram cache */
     ram_addr_t offset;
     ram_addr_t used_length;
     ram_addr_t max_length;
diff --git a/migration/migration.c b/migration/migration.c
index 8dee7dd309..cfc1b958b9 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -421,6 +421,8 @@  static void process_incoming_migration_co(void *opaque)
 
         /* Wait checkpoint incoming thread exit before free resource */
         qemu_thread_join(&mis->colo_incoming_thread);
+        /* We hold the global iothread lock, so it is safe here */
+        colo_release_ram_cache();
     }
 
     if (ret < 0) {
diff --git a/migration/ram.c b/migration/ram.c
index 912810c18e..7ca845f8a9 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -2520,6 +2520,20 @@  static inline void *host_from_ram_block_offset(RAMBlock *block,
     return block->host + offset;
 }
 
+static inline void *colo_cache_from_block_offset(RAMBlock *block,
+                                                 ram_addr_t offset)
+{
+    if (!offset_in_ramblock(block, offset)) {
+        return NULL;
+    }
+    if (!block->colo_cache) {
+        error_report("%s: colo_cache is NULL in block :%s",
+                     __func__, block->idstr);
+        return NULL;
+    }
+    return block->colo_cache + offset;
+}
+
 /**
  * ram_handle_compressed: handle the zero page case
  *
@@ -2724,6 +2738,57 @@  static void decompress_data_with_multi_threads(QEMUFile *f,
     qemu_mutex_unlock(&decomp_done_lock);
 }
 
+/*
+ * colo cache: this is for secondary VM, we cache the whole
+ * memory of the secondary VM, it is need to hold the global lock
+ * to call this helper.
+ */
+int colo_init_ram_cache(void)
+{
+    RAMBlock *block;
+
+    rcu_read_lock();
+    QLIST_FOREACH_RCU(block, &ram_list.blocks, next) {
+        block->colo_cache = qemu_anon_ram_alloc(block->used_length,
+                                                NULL,
+                                                false);
+        if (!block->colo_cache) {
+            error_report("%s: Can't alloc memory for COLO cache of block %s,"
+                         "size 0x" RAM_ADDR_FMT, __func__, block->idstr,
+                         block->used_length);
+            goto out_locked;
+        }
+    }
+    rcu_read_unlock();
+    return 0;
+
+out_locked:
+    QLIST_FOREACH_RCU(block, &ram_list.blocks, next) {
+        if (block->colo_cache) {
+            qemu_anon_ram_free(block->colo_cache, block->used_length);
+            block->colo_cache = NULL;
+        }
+    }
+
+    rcu_read_unlock();
+    return -errno;
+}
+
+/* It is need to hold the global lock to call this helper */
+void colo_release_ram_cache(void)
+{
+    RAMBlock *block;
+
+    rcu_read_lock();
+    QLIST_FOREACH_RCU(block, &ram_list.blocks, next) {
+        if (block->colo_cache) {
+            qemu_anon_ram_free(block->colo_cache, block->used_length);
+            block->colo_cache = NULL;
+        }
+    }
+    rcu_read_unlock();
+}
+
 /**
  * ram_load_setup: Setup RAM for migration incoming side
  *
@@ -2740,6 +2805,7 @@  static int ram_load_setup(QEMUFile *f, void *opaque)
 
     xbzrle_load_setup();
     ramblock_recv_map_init();
+
     return 0;
 }
 
@@ -2753,6 +2819,7 @@  static int ram_load_cleanup(void *opaque)
         g_free(rb->receivedmap);
         rb->receivedmap = NULL;
     }
+
     return 0;
 }
 
@@ -2966,7 +3033,7 @@  static int ram_load(QEMUFile *f, void *opaque, int version_id)
 
     while (!postcopy_running && !ret && !(flags & RAM_SAVE_FLAG_EOS)) {
         ram_addr_t addr, total_ram_bytes;
-        void *host = NULL;
+        void *host = NULL, *host_bak = NULL;
         uint8_t ch;
 
         addr = qemu_get_be64(f);
@@ -2986,13 +3053,36 @@  static int ram_load(QEMUFile *f, void *opaque, int version_id)
                      RAM_SAVE_FLAG_COMPRESS_PAGE | RAM_SAVE_FLAG_XBZRLE)) {
             RAMBlock *block = ram_block_from_stream(f, flags);
 
-            host = host_from_ram_block_offset(block, addr);
+             /*
+             * After going into COLO, we should load the Page into colo_cache
+             * NOTE: We need to keep a copy of SVM's ram in colo_cache.
+             * Privously, we copied all these memory in preparing stage of COLO
+             * while we need to stop VM, which is a time-consuming process.
+             * Here we optimize it by a trick, back-up every page while in
+             * migration process while COLO is enabled, though it affects the
+             * speed of the migration, but it obviously reduce the downtime of
+             * back-up all SVM'S memory in COLO preparing stage.
+             */
+            if (migration_incoming_in_colo_state()) {
+                host = colo_cache_from_block_offset(block, addr);
+                /* After goes into COLO state, don't backup it any more */
+                if (!migration_incoming_in_colo_state()) {
+                    host_bak = host;
+                }
+            }
+            if (!migration_incoming_in_colo_state()) {
+                host = host_from_ram_block_offset(block, addr);
+            }
             if (!host) {
                 error_report("Illegal RAM offset " RAM_ADDR_FMT, addr);
                 ret = -EINVAL;
                 break;
             }
-            ramblock_recv_bitmap_set(block, host);
+
+            if (!migration_incoming_in_colo_state()) {
+                ramblock_recv_bitmap_set(block, host);
+            }
+
             trace_ram_load_loop(block->idstr, (uint64_t)addr, flags, host);
         }
 
@@ -3087,6 +3177,9 @@  static int ram_load(QEMUFile *f, void *opaque, int version_id)
         if (!ret) {
             ret = qemu_file_get_error(f);
         }
+        if (!ret && host_bak && host) {
+            memcpy(host_bak, host, TARGET_PAGE_SIZE);
+        }
     }
 
     ret |= wait_for_decompress_done();
diff --git a/migration/ram.h b/migration/ram.h
index 5030be110a..66e9b86ff0 100644
--- a/migration/ram.h
+++ b/migration/ram.h
@@ -64,4 +64,8 @@  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);
 
+/* ram cache */
+int colo_init_ram_cache(void);
+void colo_release_ram_cache(void);
+
 #endif
diff --git a/migration/savevm.c b/migration/savevm.c
index c43d220220..ec0bff09ce 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -1807,7 +1807,7 @@  static int loadvm_handle_cmd_packaged(MigrationIncomingState *mis)
 static int loadvm_process_enable_colo(MigrationIncomingState *mis)
 {
     migration_incoming_enable_colo();
-    return 0;
+    return colo_init_ram_cache();
 }
 
 /*