revlog: break up compression of large deltas
Python's zlib apparently makes an internal copy of strings passed to
compress(). To avoid this, compress strings 1M at a time, then join
them at the end if the result would be smaller than the original.
For initial commits of large but compressible files, this cuts peak
memory usage nearly in half.
os = <unloaded module 'os'>
os.system = <built-in function system>
os = <module 'os' from '?'>
mercurial.version = <unloaded module 'version'>
mercurial.version.get_version = <function get_version at 0x?>
mercurial.version = <module 'mercurial.version' from '?'>
mercurial = <module 'mercurial' from '?'>
util = <unloaded module 'util'>
util.system = <function system at 0x?>
util = <module 'mercurial.util' from '?'>
util.system = <function system at 0x?>
fred = <unloaded module 're'>
re = <unloaded module 'sys'>
fred = <unloaded module 're'>
fred.sub = <function sub at 0x?>
fred = <proxied module 're'>
re = <unloaded module 'sys'>
re.stdout = <open file '<stdout>', mode 'w' at 0x?>
re = <proxied module 'sys'>