Re: [Qemu-devel] [PATCH v1 2/2] migration: add bitmap for copied page

[Peter Xu <peterx@redhat.com>]

On Tue, Jun 13, 2017 at 12:36:33PM +0300, Alexey Perevalov wrote:
> This patch adds ability to track down already copied
> 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 copied pages
> will be transferred to the software virtual bridge
> (e.g. OVS-VSWITCHD), to avoid fallocate (unmap) for
> already copied 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.
> 
> copied bitmap is not releasing due to ramblocks is not releasing
> too.
> 
> Signed-off-by: Alexey Perevalov <a.perevalov@samsung.com>
> ---
>  include/exec/ram_addr.h       |  3 +++
>  include/migration/migration.h |  3 +++
>  migration/postcopy-ram.c      |  7 ++++++
>  migration/ram.c               | 54 ++++++++++++++++++++++++++++++++++++++++++-
>  migration/ram.h               |  5 ++++
>  migration/savevm.c            |  1 +
>  6 files changed, 72 insertions(+), 1 deletion(-)
> 
> diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
> index 140efa8..56cdf16 100644
> --- a/include/exec/ram_addr.h
> +++ b/include/exec/ram_addr.h
> @@ -47,6 +47,9 @@ struct RAMBlock {
>       * of the postcopy phase
>       */
>      unsigned long *unsentmap;
> +    /* bitmap of already copied pages in postcopy */
> +    unsigned long *copiedmap;
> +    size_t nr_copiedmap;

Do we really need this?

>  };
>  
>  static inline bool offset_in_ramblock(RAMBlock *b, ram_addr_t offset)
> diff --git a/include/migration/migration.h b/include/migration/migration.h
> index 79b5484..8005c11 100644
> --- a/include/migration/migration.h
> +++ b/include/migration/migration.h
> @@ -226,4 +226,7 @@ void savevm_skip_configuration(void);
>  int global_state_store(void);
>  void global_state_store_running(void);
>  
> +size_t get_copiedmap_size(RAMBlock *rb);
> +void movecopiedmap(void *dst, RAMBlock *rb, size_t len);
> +
>  #endif
> diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
> index f6244ee..e13b22e 100644
> --- a/migration/postcopy-ram.c
> +++ b/migration/postcopy-ram.c
> @@ -576,6 +576,13 @@ int postcopy_place_page(MigrationIncomingState *mis, void *host, void *from,
>      copy_struct.len = pagesize;
>      copy_struct.mode = 0;
>  
> +
> +    /* copied 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_copiedmap_by_addr(host, rb);
> +

I guess this is not enough?

For postcopy, you may have missed to trap in
postcopy_place_page_zero() when pagesize == getpagesize() (we used
UFFDIO_ZEROPAGE there)?

(Btw, why not we trap all these in ram_load_postcopy()?)

For precopy, looks like it's missing as well? I believe it's in
ram_load().

>      /* copy also acks to the kernel waking the stalled thread up
>       * TODO: We can inhibit that ack and only do it if it was requested
>       * which would be slightly cheaper, but we'd have to be careful
> diff --git a/migration/ram.c b/migration/ram.c
> index 4ed7c2c..8466e59 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -149,6 +149,58 @@ out:
>      return ret;
>  }
>  
> +void init_copiedmap(void)
> +{
> +    RAMBlock *rb;

(Nit: better with a new line after parameters.)

> +    RAMBLOCK_FOREACH(rb) {
> +        unsigned long pages;
> +        pages = rb->max_length >> find_first_bit(&rb->page_size,
> +                8 * sizeof(rb->page_size));
> +        /* need for destination, bitmap_new calls
> +         * g_try_malloc0 and this function
> +         * Attempts to allocate @n_bytes, initialized to 0'sh */
> +        rb->copiedmap = bitmap_new(pages);
> +        rb->nr_copiedmap = pages;
> +    }
> +}
> +
> +static unsigned long int get_copied_bit_offset(void *host_addr, RAMBlock *rb)
> +{
> +    uint64_t host_addr_offset = (uint64_t)(uintptr_t)(host_addr
> +                                                      - (void *)rb->host);
> +    int page_shift = find_first_bit(&rb->page_size, 8 * sizeof(rb->page_size));
> +
> +    return host_addr_offset >> page_shift;
> +}
> +
> +int test_copiedmap_by_addr(void *host_addr, RAMBlock *rb)
> +{
> +    return test_bit(get_copied_bit_offset(host_addr, rb), rb->copiedmap);
> +}
> +
> +void set_copiedmap_by_addr(void *host_addr, RAMBlock *rb)
> +{
> +    set_bit_atomic(get_copied_bit_offset(host_addr, rb), rb->copiedmap);
> +}
> +
> +size_t get_copiedmap_size(RAMBlock *rb)
> +{
> +    return rb->nr_copiedmap;
> +}

As commented by Juan, I think we need per-TARGET_PAGE_SIZE bitmap. If
so, we should be able to get rid of these helpers?

> +
> +/*
> + * This function copies copiedmap from RAMBlock into
> + * dst memory region
> + *
> + * @dst destination address
> + * @rb RAMBlock source
> + * @len length in bytes
> + */
> +void movecopiedmap(void *dst, RAMBlock *rb, size_t len)
> +{
> +    memcpy(dst, rb->copiedmap, len);
> +}
> +
>  /*
>   * An outstanding page request, on the source, having been received
>   * and queued
> @@ -1852,11 +1904,11 @@ int ram_discard_range(const char *rbname, uint64_t start, size_t length)
>  {
>      int ret = -1;
>  
> -    trace_ram_discard_range(rbname, start, length);
>  
>      rcu_read_lock();
>      RAMBlock *rb = qemu_ram_block_by_name(rbname);
>  
> +    trace_ram_discard_range(rbname, start, length);

Why this move?

And still, we need logic for the discard during postcopy?

Thanks,

>      if (!rb) {
>          error_report("ram_discard_range: Failed to find block '%s'", rbname);
>          goto err;
> diff --git a/migration/ram.h b/migration/ram.h
> index c9563d1..dc781c1 100644
> --- a/migration/ram.h
> +++ b/migration/ram.h
> @@ -67,4 +67,9 @@ 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_copiedmap(void);
> +int test_copiedmap_by_addr(void *host_addr, RAMBlock *rb);
> +void set_copiedmap_by_addr(void *host_addr, RAMBlock *rb);
> +
>  #endif
> diff --git a/migration/savevm.c b/migration/savevm.c
> index 9c320f5..7b3726a 100644
> --- a/migration/savevm.c
> +++ b/migration/savevm.c
> @@ -1385,6 +1385,7 @@ static int loadvm_postcopy_handle_advise(MigrationIncomingState *mis)
>          return -1;
>      }
>  
> +    init_copiedmap();
>      remote_pagesize_summary = qemu_get_be64(mis->from_src_file);
>      local_pagesize_summary = ram_pagesize_summary();
>  
> -- 
> 1.9.1
> 

Thanks,

-- 
Peter Xu