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

Hi, sorry for the resend. My mailer mangled the previous attempt. 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?