From 38be603bce83307326abe3f6e9ed13ffcbb04d3f Mon Sep 17 00:00:00 2001
From: Eric Wong <e@80x24.org>
Date: Fri, 5 Jan 2018 11:17:38 +0000
Subject: [PATCH] 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
---
 ext/zlib/zlib.c | 54 +++++++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 45 insertions(+), 9 deletions(-)

diff --git a/ext/zlib/zlib.c b/ext/zlib/zlib.c
index 7906e0fba3..4ccdfd7d65 100644
--- a/ext/zlib/zlib.c
+++ b/ext/zlib/zlib.c
@@ -845,19 +845,50 @@ zstream_append_input(struct zstream *z, const Bytef *src, long len)
 static void
 zstream_discard_input(struct zstream *z, long len)
 {
-    if (NIL_P(z->input) || RSTRING_LEN(z->input) <= len) {
-	z->input = Qnil;
+    if (NIL_P(z->input)) {
     }
-    else {
-	z->input = rb_str_substr(z->input, len,
-				 RSTRING_LEN(z->input) - len);
+    else if (RBASIC_CLASS(z->input) == 0) {
+	/* hidden, we created z->input and have complete control */
+	char *ptr;
+	long oldlen, newlen;
+
+	RSTRING_GETMEM(z->input, ptr, oldlen);
+	newlen = oldlen - len;
+	if (newlen > 0) {
+	    memmove(ptr, ptr + len, newlen);
+	}
+	if (newlen < 0) {
+	    newlen = 0;
+	}
+	rb_str_resize(z->input, newlen);
+	if (newlen == 0) {
+	    rb_gc_force_recycle(z->input);
+	    z->input = Qnil;
+	}
+	else {
+	    rb_str_set_len(z->input, newlen);
+	}
+    }
+    else { /* do not mangle user-provided data */
+	if (RSTRING_LEN(z->input) <= len) {
+	    z->input = Qnil;
+	}
+	else {
+	    z->input = rb_str_substr(z->input, len,
+				     RSTRING_LEN(z->input) - len);
+	}
     }
 }
 
 static void
 zstream_reset_input(struct zstream *z)
 {
-    z->input = Qnil;
+    if (!NIL_P(z->input) && RBASIC_CLASS(z->input) == 0) {
+	rb_str_resize(z->input, 0);
+    }
+    else {
+	z->input = Qnil;
+    }
 }
 
 static void
@@ -994,7 +1025,7 @@ zstream_run(struct zstream *z, Bytef *src, long len, int flush)
 {
     struct zstream_run_args args;
     int err;
-    VALUE guard = Qnil;
+    VALUE old_input = Qnil;
 
     args.z = z;
     args.flush = flush;
@@ -1013,7 +1044,8 @@ zstream_run(struct zstream *z, Bytef *src, long len, int flush)
 	/* keep reference to `z->input' so as not to be garbage collected
 	   after zstream_reset_input() and prevent `z->stream.next_in'
 	   from dangling. */
-	guard = z->input;
+	old_input = zstream_detach_input(z);
+	rb_obj_hide(old_input);
     }
 
     if (z->stream.avail_out == 0) {
@@ -1051,7 +1083,10 @@ loop:
 
     if (z->stream.avail_in > 0) {
 	zstream_append_input(z, z->stream.next_in, z->stream.avail_in);
-	RB_GC_GUARD(guard); /* prevent tail call to make guard effective */
+    }
+    if (!NIL_P(old_input)) {
+	rb_str_resize(old_input, 0);
+	rb_gc_force_recycle(old_input);
     }
 
     if (args.jump_state)
@@ -2330,6 +2365,7 @@ gzfile_write_raw(struct gzfile *gz)
 	str = zstream_detach_buffer(&gz->z);
 	OBJ_TAINT(str);  /* for safe */
 	rb_funcall(gz->io, id_write, 1, str);
+	rb_str_resize(str, 0);
 	if ((gz->z.flags & GZFILE_FLAG_SYNC)
 	    && rb_respond_to(gz->io, id_flush))
 	    rb_funcall(gz->io, id_flush, 0);
-- 
EW