[Libguestfs] [PATCH] Improve memory management of nbdkit python plugin example

[Carl-Daniel Hailfinger]

Hi,

On 26.09.2016 17:19, Pino Toscano wrote:
> On Monday, 26 September 2016 17:07:41 CEST Carl-Daniel Hailfinger wrote: >> the nbdkit python plugin example has suboptimal memory management:
>> - it creates the disk image as a string on init >> - it casts the
string to bytearray on every read >> - it copies the string before and
the string after the written region, >> then reassembles those pieces
together with the written region to a new >> disk image string >> >>
This is not a problem as long as the image is small, but in my tests >>
with a 5 GB sized image nbdkit already used 15 GB RAM directly after >>
startup, and even more (20-25 GB) on the first write. >> >> This changes
the code to use bytearray everywhere and use the proper >> methods to
change bytearray objects directly. With the patch applied, >> nbdkit
with a 5 GB image will still only use 5 GB RAM even during heavy >>
read/write activity. >> >> Regards, >> Carl-Daniel >> >> diff -r
521366d1854b -r d7d5078d08c7 plugins/python/example.py >> ---
a/plugins/python/example.py    Sun Jul 10 17:10:30 2016 +0100 >> +++
b/plugins/python/example.py    Sun Sep 25 05:04:02 2016 +0200 >> @@
-29,7 +29,7 @@ >>  # reconnect to the same server you should see the
same disk.  You >>  # could also put this into the handle, so there
would be a fresh disk >>  # per handle. >> -disk = "\0" * (1024*1024);
>> +disk = bytearray(1024 * 1024) >>  >>  # This just prints the extra
command line parameters, but real plugins >>  # should parse them and
reject any unknown parameters. >> @@ -50,9 +50,9 @@ >>  >>  def pread(h,
count, offset): >>      global disk >> -    return bytearray
(disk[offset:offset+count]) >> +    return disk[offset:offset+count] >> 
>>  def pwrite(h, buf, offset): >>      global disk >>      end = offset
+ len (buf) >> -    disk = disk[:offset] + buf + disk[end:] >> +   
disk[offset:end] = buf > > I'd look fine to me -- I guess it should work
with both Python 2 and 3, > right?

Indeed. By the way, does anyone know if there is a Python 3 plugin
infrastructure for nbdkit?

Regards,
Carl-Daniel