Re: [Qemu-devel] [PATCH 04/27] add a version number to ram_list

[Michael Roth <mdroth@linux.vnet.ibm.com>]

On Tue, Jul 24, 2012 at 08:36:29PM +0200, Juan Quintela wrote:
> From: Umesh Deshpande <udeshpan@redhat.com>
> 
> This will be used to detect if last_block might have become invalid
> across different calls to ram_save_live.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Umesh Deshpande <udeshpan@redhat.com>
> Signed-off-by: Juan Quintela <quintela@redhat.com>
> ---
>  arch_init.c |    6 ++++++
>  cpu-all.h   |    1 +
>  exec.c      |    4 ++++
>  3 files changed, 11 insertions(+)
> 
> diff --git a/arch_init.c b/arch_init.c
> index 02d36ce..9e05aae 100644
> --- a/arch_init.c
> +++ b/arch_init.c
> @@ -340,6 +340,7 @@ static int save_xbzrle_page(QEMUFile *f, uint8_t *current_data,
> 
>  static RAMBlock *last_block;
>  static ram_addr_t last_offset;
> +static uint32_t last_version;
> 
>  /*
>   * ram_save_block: Writes a page of memory to the stream f
> @@ -496,6 +497,7 @@ static void reset_ram_globals(void)
>  {
>      last_block = NULL;
>      last_offset = 0;
> +    last_version = ram_list.version;
>      sort_ram_list();
>  }
> 
> @@ -554,6 +556,10 @@ static int ram_save_iterate(QEMUFile *f, void *opaque)
>      int i;
>      uint64_t expected_time;
> 
> +    if (ram_list.version != last_version) {
> +        reset_ram_globals();
> +    }
> +

Was it a bug in the old code to not do this? In the unthreaded version
it looks like last_block could still become invalid between iterations if it
was removed in the meantime, so I'm trying to understand why it's needed
now.

And why do we re-sort when this happens? The old implementation didn't
seem to place any guarantees on the block ordering beyond the initial
sorting by block->idstr. After that they were sent in MRU order.

>      bytes_transferred_last = bytes_transferred;
>      bwidth = qemu_get_clock_ns(rt_clock);
> 
> diff --git a/cpu-all.h b/cpu-all.h
> index ca3bb24..429b2c6 100644
> --- a/cpu-all.h
> +++ b/cpu-all.h
> @@ -486,6 +486,7 @@ typedef struct RAMBlock {
> 
>  typedef struct RAMList {
>      uint8_t *phys_dirty;
> +    uint32_t version;
>      QLIST_HEAD(, RAMBlock) blocks_mru;
>      QLIST_HEAD(, RAMBlock) blocks;
>      uint64_t dirty_pages;
> diff --git a/exec.c b/exec.c
> index afc472f..ceffa4f 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -2555,6 +2555,8 @@ ram_addr_t qemu_ram_alloc_from_ptr(ram_addr_t size, void *host,
>      QLIST_INSERT_HEAD(&ram_list.blocks, new_block, next);
>      QLIST_INSERT_HEAD(&ram_list.blocks_mru, new_block, next_mru);
> 
> +    ram_list.version++;
> +
>      ram_list.phys_dirty = g_realloc(ram_list.phys_dirty,
>                                         last_ram_offset() >> TARGET_PAGE_BITS);
>      cpu_physical_memory_set_dirty_range(new_block->offset, size, 0xff);
> @@ -2578,6 +2580,7 @@ void qemu_ram_free_from_ptr(ram_addr_t addr)
>          if (addr == block->offset) {
>              QLIST_REMOVE(block, next);
>              QLIST_REMOVE(block, next_mru);
> +            ram_list.version++;
>              g_free(block);
>              return;
>          }
> @@ -2592,6 +2595,7 @@ void qemu_ram_free(ram_addr_t addr)
>          if (addr == block->offset) {
>              QLIST_REMOVE(block, next);
>              QLIST_REMOVE(block, next_mru);
> +            ram_list.version++;
>              if (block->flags & RAM_PREALLOC_MASK) {
>                  ;
>              } else if (mem_path) {
> -- 
> 1.7.10.4
> 
>