From: "martinemde (Martin Emde) via ruby-core" <ruby-core@ml.ruby-lang.org>
To: ruby-core@ml.ruby-lang.org
Cc: "martinemde (Martin Emde)" <noreply@ruby-lang.org>
Subject: [ruby-core:117497] [Ruby master Bug#20424] ZLib::GZipReader always double allocates strings when passed outbuf, significantly increasing memory usage
Date: Thu, 11 Apr 2024 19:20:33 +0000 (UTC) [thread overview]
Message-ID: <redmine.issue-20424.20240411192033.1181@ruby-lang.org> (raw)
In-Reply-To: redmine.issue-20424.20240411192033.1181@ruby-lang.org
Issue #20424 has been reported by martinemde (Martin Emde).
----------------------------------------
Bug #20424: ZLib::GZipReader always double allocates strings when passed outbuf, significantly increasing memory usage
https://bugs.ruby-lang.org/issues/20424
* Author: martinemde (Martin Emde)
* Status: Open
* ruby -v: ruby 3.3.0 (2023-12-25 revision 5124f9ac75) [arm64-darwin23]
* Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN
----------------------------------------
In trying to improve the memory performance during the install of rubygems, we previously found a bug in `eof?`. Further investigation into the memory usage during the fix for this bug found wasteful allocating of strings in readpartial and read.
In ZLib, when reading with readpartial or read, a new string is always created for the bytes read from the buffer.
The current approach allocates a string no matter if there is an outbuf passed.
```
# vastly simplified psuedo implementation
def readpartial(len, dst=nil)
if (buffer.empty?)
buffer = gzipfile.readpartial(len, dst) # adds inflated bytes into dst if passed
end
dst = allocate_new_string(len) # make a new string for the destination
dst << buffer.read(len) # read from the buffer into the destination
end
```
The result is that readpartial always allocated at least double the bytes necessary.
Samuel Giddins submitted, and I have tested and reviewed, [a pull request, zlib#61](https://github.com/ruby/zlib/pull/61) that resolves the issue and vastly improves the memory usage and increases the speed of GZipReader by avoiding excess memcpy and rb_str_new calls that were wasted.
This PR also adds an outbuf to GZipReader#read for improvement memory management, very similar to [IO#read](https://ruby-doc.org/core-2.5.1/IO.html#method-i-read)
We appreciate your attention to this performance improvement. We believe it will further improve the performance of rubygems gem installs.
--
https://bugs.ruby-lang.org/
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parent reply other threads:[~2024-04-11 19:20 UTC|newest]
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