[ruby-core:84642] [Ruby trunk Feature#14315] zlib: reduce garbage on gzip writes (deflate)

Issue #14315 has been updated by shevegen (Robert A. Heiler).


I forgot to add - if approved, it could also be (additionally or
not) be part of the expanded "shebang" information for ruby,
similar to how frozen string literals would work.

# frozen_string_literal: true

like

# warnings: verbose

Or something like that.

I assume that we probably can not pack too much information on the
top of all .rb files, so this is perhaps not a great suggestion
from me, but I just wanted to mention it. (And a commandline switch
to ruby too, like --enable-verbose-warnings or just --verbose-warnings)

Note that this applies only if the general direction for more 
fine-tuned warning messages is approved by matz. Since this may 
impact several areas of ruby, I assume that this may not be 
approved until some thorough prior discussion anyway - and I also
do not intend to distract from the initial suggestion by the 
threadstarter. I only wanted to refer to the overall situation again.

----------------------------------------
Feature #14315: zlib: reduce garbage on gzip writes (deflate)
https://bugs.ruby-lang.org/issues/14315#change-69218

* Author: normalperson (Eric Wong)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
```
zlib: reduce garbage on gzip writes (deflate)

Zlib::GzipWriter generated large amounts of garbage from
(struct zstream).input.  Reuse the .input field when it is
hidden, and recycle it when its lifetime is over.  This change
alone reduced memory usage of the writer from 90MB to 4.5MB.

For the detached buffer of compressed data used by
gzfile_write_raw, we can only clear the string (not recycle it)
since user code may hold references to it (but the data would be
clobbered, anyways).  This reduced memory usage slightly by
around 0.5MB (because it's smaller compressed data).

Combined, these changes reduce the anonymous RSS memory of a
dedicated writer process from over 90MB to under 4MB.

before:

    #      user     system      total        real

    writer   7.823332   0.053333   7.876665 (  7.881464)
    writer RssAnon:    92944 kB
    reader   6.969999   0.076666   7.046665 (  7.906377)
    reader RssAnon:   109820 kB

after:

    writer   7.359999   0.000000   7.359999 (  7.360639)
    writer RssAnon:     4040 kB
    reader   6.346667   0.070000   6.416667 (  7.387654)
    reader RssAnon:    98272 kB

Script used:
-------
require 'zlib'
require 'benchmark'
nr = 16384 * 2

def stats(pfx, bm)
  str = "#{bm}#{File.readlines("/proc/#$$/status").grep(/^RssAnon:/)[0]}"
  puts str.gsub!(/^/m, pfx)
end

rd, wr = IO.pipe
pid = fork do
  buf = ((0..255).map(&:chr).join * 128).freeze
  rd.close
  gzip = Zlib::GzipWriter.new(wr)
  bm = Benchmark.measure do
    nr.times { gzip.write(buf) }
    gzip.close
    wr.close
  end
  stats('writer ', bm)
end

wr.close
buf = ''
gunzip = Zlib::GzipReader.new(rd)
n = 0
bm = Benchmark.measure do
  begin
    gunzip.readpartial(16384, buf)
    n += buf.size
  rescue EOFError
    break
  end while true
end
stats('reader ', bm)
Process.waitall
-------
* ext/zlib/zlib.c (zstream_discard_input): reuse or recycle hidden input
  (zstream_reset_input): clear hidden input
  (zstream_run): detach input and recycle after use
  (gzfile_write_raw): clear buffer after write
```


---Files--------------------------------
0001-zlib-reduce-garbage-on-gzip-writes-deflate.patch (4.91 KB)


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