Re: [Qemu-devel] [PATCH v13 11/13] Add XBZRLE to ram_save_block and ram_save_live

[Orit Wasserman]

On 06/27/2012 10:56 PM, Eric Blake wrote:
> On 06/27/2012 04:34 AM, Orit Wasserman wrote:
>> In the outgoing migration check to see if the page is cached and
>> changed than send compressed page by using save_xbrle_page function.
>> In the incoming migration check to see if RAM_SAVE_FLAG_XBRLE is set
>> and decompress the page (by using load_xbrle function).
> 
> Mismatch between commit comment and actual code (XBRLE vs. XBZRLE).
> 
> 
>> +
>> +    /* Stage 1 cache the page and exit.
>> +       Stage 2 check to see if page is cached , if not cache the page.
> 
> s/cached ,/cached,/
> 
> 
>> +    if (encoded_len == 0) {
>> +        DPRINTF("Unmodifed page skipping\n");
> 
> spelling and grammar:
> s/Unmodifed page skipping/Skipping unmodified page/
> 
> 
>>      if (!block)
>>          block = QLIST_FIRST(&ram_list.blocks);
>>  
>> +
>> +
>>      do {
> 
> Why the spurious whitespace addition?
> 
> 
>> +            } else if (migrate_use_xbzrle() && stage != 3) {
>> +                current_addr = block->offset + offset;
>> +                /* In stage 1 we only cache the pages before sending them
>> +                   from the cache (uncompressed).
>> +                   We doen't use compression for stage 3.
> 
> s/doen't/don't/
> 
>> +
>> +            /* either we didn't send yet (we may got XBZRLE overflow) */
> 
> s/may got/may have had/
> 
>>  
>> -            break;
>> +            /* if page is unmodified lets continue to the next */
> 
> s/lets/let's/
> 
> or even shorter:
> 
> s/ lets/,/
> 
>> @@ -331,6 +440,17 @@ int ram_save_live(QEMUFile *f, int stage, void *opaque)
>>          last_offset = 0;
>>          sort_ram_list();
>>  
>> +        if (migrate_use_xbzrle()) {
>> +            XBZRLE.cache = cache_init(migrate_xbzrle_cache_size() /
>> +                                      TARGET_PAGE_SIZE,
>> +                                      TARGET_PAGE_SIZE);
>> +            if (!XBZRLE.cache) {
>> +                DPRINTF("Error creating cache\n");
>> +                return -1;
>> +            }
>> +            XBZRLE.encoded_buf = g_malloc0(TARGET_PAGE_SIZE);
> 
> This guarantees long alignment (good, per my proposed g_assert in
> 10/13), but not page alignment.  Do we get any benefits by using a
> different allocation to guarantee page alignment?  (Off-hand, I'm not
> thinking of any.)
> 
>> @@ -389,7 +509,7 @@ int ram_save_live(QEMUFile *f, int stage, void *opaque)
>>          while ((bytes_sent = ram_save_block(f, stage)) != -1) {
>>              bytes_transferred += bytes_sent;
>>          }
>> -        memory_global_dirty_log_stop();
>> +        migration_end();
>>      }
>>  
>>      qemu_put_be64(f, RAM_SAVE_FLAG_EOS);
> 
> This hunk should have been squashed into 9/13.
> 
>> @@ -512,6 +675,16 @@ int ram_load(QEMUFile *f, void *opaque, int version_id)
>>              host = host_from_stream_offset(f, addr, flags);
>>  
>>              qemu_get_buffer(f, host, TARGET_PAGE_SIZE);
>> +        } else if (flags & RAM_SAVE_FLAG_XBZRLE) {
> 
> We should probably be erroring out if we detect this incoming flag, but
> the management app explicitly disabled the xbzrle migration capability,
> since that represents a case of user error, and failing the migration is
> better than proceeding to decode things anyway.
> 
correct, I will fix it.

Orit