[ruby-core:64444] [ruby-trunk - Bug #9934] High memory usage from file_expand_path_*

Issue #9934 has been updated by Tomoyuki Chikanaga.

Backport changed from 2.0.0: REQUIRED, 2.1: REQUIRED to 2.0.0: REQUIRED, 2.1: DONE

r46408, r46410, r46413, r46414, r46424, r46436, r46437 and partially r44827 (to resolve conflict of r46408) were backported into `ruby_2_1` branch at r47215.

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Bug #9934: High memory usage from file_expand_path_*
https://bugs.ruby-lang.org/issues/9934#change-48394

* Author: Aman Gupta
* Status: Closed
* Priority: Normal
* Assignee: 
* Category: core
* Target version: current: 2.2.0
* ruby -v: current
* Backport: 2.0.0: REQUIRED, 2.1: DONE
----------------------------------------
All the file expansion routines use `EXPAND_PATH_BUFFER()` which allocates PATH_MAX bytes on the heap per invocation.
The strings returned by `File.expand_path` are never realloc'd after they are populated, so they continue using 4kb (on linux) per string.
In our rails app, 22MB of heap usage is due to expanded path name strings.

~~~
$ ruby -robjspace -e' puts ObjectSpace.dump(File.expand_path("/foo")) '
{"address":"0x007fa2b44dd6c8", "type":"STRING", "class":"0x007fa2b3f99608", "bytesize":4, "capacity":4098, "value":"/foo", "encoding":"US-ASCII", "memsize":4099, "flags":{"wb_protected":true}}
~~~

The following failing patch demonstrates the issue as well:

~~~diff
diff --git a/test/ruby/test_file_exhaustive.rb b/test/ruby/test_file_exhaustive.rb
index 2c945ea..49be9de 100644
--- a/test/ruby/test_file_exhaustive.rb
+++ b/test/ruby/test_file_exhaustive.rb
@@ -458,6 +458,12 @@ class TestFileExhaustive < Test::Unit::TestCase
     end
   end

+  def test_expand_path_memsize
+    require "objspace"
+    path = File.expand_path("/foo")
+    assert_equal 5, ObjectSpace.memsize_of(path)
+  end
+
   def test_expand_path_encoding
     drive = (DRIVE ? 'C:' : '')
     if Encoding.find("filesystem") == Encoding::CP1251
~~~



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