Re: [Qemu-devel] [PATCH v2 3/3] migration: add bitmap for received page

[Dr. David Alan Gilbert]

* Alexey Perevalov (address@hidden) wrote:
> This patch adds ability to track down already received
> pages, it's necessary for calculation vCPU block time in
> postcopy migration feature, maybe for restore after
> postcopy migration failure.
> Also it's necessary to solve shared memory issue in
> postcopy livemigration. Information about received pages
> will be transferred to the software virtual bridge
> (e.g. OVS-VSWITCHD), to avoid fallocate (unmap) for
> already received pages. fallocate syscall is required for
> remmaped shared memory, due to remmaping itself blocks
> ioctl(UFFDIO_COPY, ioctl in this case will end with EEXIT
> error (struct page is exists after remmap).
> 
> Bitmap is placed into RAMBlock as another postcopy/precopy
> related bitmaps.
> 
> Signed-off-by: Alexey Perevalov <address@hidden>
> ---
>  include/exec/ram_addr.h  |  2 ++
>  migration/postcopy-ram.c | 11 ++++++++---
>  migration/ram.c          | 33 +++++++++++++++++++++++++++++++++
>  migration/ram.h          |  5 +++++
>  migration/savevm.c       |  1 +
>  5 files changed, 49 insertions(+), 3 deletions(-)
> 
> diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
> index 140efa8..c2c1dfe 100644
> --- a/include/exec/ram_addr.h
> +++ b/include/exec/ram_addr.h
> @@ -47,6 +47,8 @@ struct RAMBlock {
>       * of the postcopy phase
>       */
>      unsigned long *unsentmap;
> +    /* bitmap of already received pages in postcopy */
> +    unsigned long *receivedmap;
>  };
>  
>  static inline bool offset_in_ramblock(RAMBlock *b, ram_addr_t offset)
> diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
> index 38a429a..5ac3ed2 100644
> --- a/migration/postcopy-ram.c
> +++ b/migration/postcopy-ram.c
> @@ -562,8 +562,13 @@ int postcopy_ram_enable_notify(MigrationIncomingState 
> *mis)
>  }
>  
>  static int qemu_ufd_copy_ioctl(int userfault_fd, void *host_addr,
> -        void *from_addr, uint64_t pagesize)
> +        void *from_addr, uint64_t pagesize, RAMBlock *rb)
>  {
> +    /* received page isn't feature of blocktime calculation,
> +     * it's more general entity, so keep it here,
> +     * but gup betwean two following operation could be high,
> +     * and in this case blocktime for such small interval will be lost */
> +    set_receivedmap_by_addr(host_addr, rb);
>      if (from_addr) {
>          struct uffdio_copy copy_struct;
>          copy_struct.dst = (uint64_t)(uintptr_t)host_addr;
> @@ -595,7 +600,7 @@ int postcopy_place_page(MigrationIncomingState *mis, void 
> *host, void *from,
>       * which would be slightly cheaper, but we'd have to be careful
>       * of the order of updating our page state.
>       */
> -    if (qemu_ufd_copy_ioctl(mis->userfault_fd, host, from, pagesize)) {
> +    if (qemu_ufd_copy_ioctl(mis->userfault_fd, host, from, pagesize, rb)) {

In your first patch of the series you changed postcopy_place_page to
take a RAMBlock* *rather* than a pagesize; perhaps it would be better
to do the same here?

Other than that looks pretty good.

Dave

>          int e = errno;
>          error_report("%s: %s copy host: %p from: %p (size: %zd)",
>                       __func__, strerror(e), host, from, pagesize);
> @@ -619,7 +624,7 @@ int postcopy_place_page_zero(MigrationIncomingState *mis, 
> void *host,
>  
>      pagesize = qemu_ram_pagesize(rb);
>      if (pagesize == getpagesize()) {
> -        if (qemu_ufd_copy_ioctl(mis->userfault_fd, host, 0, getpagesize())) {
> +        if (qemu_ufd_copy_ioctl(mis->userfault_fd, host, 0, getpagesize(), 
> rb)) {
>              int e = errno;
>              error_report("%s: %s zero host: %p",
>                           __func__, strerror(e), host);
> diff --git a/migration/ram.c b/migration/ram.c
> index f50479d..f5ea3c2 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -151,6 +151,34 @@ out:
>      return ret;
>  }
>  
> +void init_receivedmap(void)
> +{
> +    RAMBlock *rb;
> +
> +    RAMBLOCK_FOREACH(rb) {
> +        unsigned long pages;
> +        pages = rb->max_length >> TARGET_PAGE_BITS;
> +        rb->receivedmap = bitmap_new(pages);
> +    }
> +}
> +
> +static unsigned long int get_received_bit_offset(void *host_addr, RAMBlock 
> *rb)
> +{
> +    uint64_t host_addr_offset = (uint64_t)(uintptr_t)(host_addr
> +                                                      - (void *)rb->host);
> +    return host_addr_offset >> TARGET_PAGE_BITS;
> +}
> +
> +int test_receivedmap_by_addr(void *host_addr, RAMBlock *rb)
> +{
> +    return test_bit(get_received_bit_offset(host_addr, rb), rb->receivedmap);
> +}
> +
> +void set_receivedmap_by_addr(void *host_addr, RAMBlock *rb)
> +{
> +    set_bit_atomic(get_received_bit_offset(host_addr, rb), rb->receivedmap);
> +}
> +
>  /*
>   * An outstanding page request, on the source, having been received
>   * and queued
> @@ -2324,8 +2352,13 @@ static int ram_load_setup(QEMUFile *f, void *opaque)
>  
>  static int ram_load_cleanup(void *opaque)
>  {
> +    RAMBlock *rb;
>      xbzrle_load_cleanup();
>      compress_threads_load_cleanup();
> +
> +    RAMBLOCK_FOREACH(rb) {
> +        g_free(rb->receivedmap);
> +    }
>      return 0;
>  }
>  
> diff --git a/migration/ram.h b/migration/ram.h
> index c081fde..7048ff9 100644
> --- a/migration/ram.h
> +++ b/migration/ram.h
> @@ -52,4 +52,9 @@ int ram_discard_range(const char *block_name, uint64_t 
> start, size_t length);
>  int ram_postcopy_incoming_init(MigrationIncomingState *mis);
>  
>  void ram_handle_compressed(void *host, uint8_t ch, uint64_t size);
> +
> +void init_receivedmap(void);
> +int test_receivedmap_by_addr(void *host_addr, RAMBlock *rb);
> +void set_receivedmap_by_addr(void *host_addr, RAMBlock *rb);
> +
>  #endif
> diff --git a/migration/savevm.c b/migration/savevm.c
> index 31158da..668d3bb 100644
> --- a/migration/savevm.c
> +++ b/migration/savevm.c
> @@ -1372,6 +1372,7 @@ static int 
> loadvm_postcopy_handle_advise(MigrationIncomingState *mis)
>          return -1;
>      }
>  
> +    init_receivedmap();
>      remote_pagesize_summary = qemu_get_be64(mis->from_src_file);
>      local_pagesize_summary = ram_pagesize_summary();
>  
> -- 
> 1.9.1
> 
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK