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Hard question: Any ideas why this code leaks memory?

Sven C. Koehler

8/19/2008 7:46:00 PM

Hello,

could someone help me understand why this code leaks memory? (I am using
ruby 1.8.6 (2007-12-03 patchlevel 113) [x86_64-linux].)

def rss_leaks
/^VmRSS:\s+(\d+)/m.match(File.open("/proc/#{$$}/status") {|f|
f.read })[1].to_i
end

| irb(main):002:0> 100000.times { rss_leaks }; rss_leaks
| => 11624
| irb(main):003:0> 100000.times { rss_leaks }; rss_leaks
| => 16836
| irb(main):004:0> 100000.times { rss_leaks }; rss_leaks
| => 22008
| irb(main):005:0> 100000.times { rss_leaks }; rss_leaks
| => 27248
| irb(main):006:0> 100000.times { rss_leaks }; rss_leaks
| => 32468

Calling GC.start inbetween does not help, but when we rewrote rss_leaks
this way the leaks disappeared:

def rss_no_leaks()
d = File.open("/proc/#{$$}/status") {|f| f.read }
/^VmRSS:\s+(\d+)/m.match(d)[1].to_i
end

| irb(main):002:0> 100000.times { rss_no_leaks }; rss_no_leaks
| => 6568
| irb(main):003:0> 100000.times { rss_no_leaks }; rss_no_leaks
| => 6568
| irb(main):004:0> 100000.times { rss_no_leaks }; rss_no_leaks
| => 6588
| irb(main):005:0> 100000.times { rss_no_leaks }; rss_no_leaks
| => 6592
| irb(main):006:0> 100000.times { rss_no_leaks }; rss_no_leaks
| => 6572

Any help to further understand what actually causes these leaks would be
very appreaciated!

Best wishes,

Sven
7 Answers

Xavier Noria

8/20/2008 12:28:00 AM

0

On Tue, Aug 19, 2008 at 9:46 PM, Sven C. Koehler <schween@snafu.de> wrote:

> def rss_leaks
> /^VmRSS:\s+(\d+)/m.match(File.open("/proc/#{$$}/status") {|f|
> f.read })[1].to_i
> end

No idea about the leak, just wanted to point out for the archives that
/m does nothing there because there's no dot.

/m in Ruby is /s in Perl ("." matches "\n"), and Perl's /m (multi-line
mode) is always on in Ruby, there's no way to switch that one off. ^
is always beginning of line, and you assert beginning of string with
\A. To tangle this a little more /s in Ruby exists and means the
regexp is written in the SJIS encoding.

Nobuyoshi Nakada

8/20/2008 2:50:00 AM

0

Hi,

At Wed, 20 Aug 2008 04:46:24 +0900,
Sven C. Koehler wrote in [ruby-talk:311847]:
> could someone help me understand why this code leaks memory? (I am using
> ruby 1.8.6 (2007-12-03 patchlevel 113) [x86_64-linux].)
>
> def rss_leaks
> /^VmRSS:\s+(\d+)/m.match(File.open("/proc/#{$$}/status") {|f|
> f.read })[1].to_i
> end

> Calling GC.start inbetween does not help, but when we rewrote rss_leaks
> this way the leaks disappeared:
>
> def rss_no_leaks()
> d = File.open("/proc/#{$$}/status") {|f| f.read }
> /^VmRSS:\s+(\d+)/m.match(d)[1].to_i
> end

Seems a bug.

--
Nobu Nakada

Sven C. Koehler

8/20/2008 3:50:00 AM

0

On Wed, Aug 20, 2008 at 11:50:16AM +0900, Nobuyoshi Nakada wrote:
> Seems a bug.

Yep, and it seems to be fixed in 1.8.7-p71 :
http://rubyforge.org/tracker/?func=detail&aid=15425&group_id=426&...

-S.

Nobuyoshi Nakada

8/20/2008 6:41:00 AM

0

Hi,

At Wed, 20 Aug 2008 12:49:41 +0900,
Sven C. Koehler wrote in [ruby-talk:311908]:
> Yep, and it seems to be fixed in 1.8.7-p71 :
> http://rubyforge.org/tracker/?func=detail&aid=15425&group_id=426&...

Hmmm, indeed. But it seems to occur with the latest 1.8.

--
Nobu Nakada

Sven C. Koehler

8/20/2008 11:20:00 AM

0

On Wed, Aug 20, 2008 at 03:44:15PM +0900, Nobuyoshi Nakada wrote:
> At Wed, 20 Aug 2008 12:49:41 +0900,
> Sven C. Koehler wrote in [ruby-talk:311908]:
> > Yep, and it seems to be fixed in 1.8.7-p71 :
> > http://rubyforge.org/tracker/?func=detail&aid=15425&group_id=426&...
>
> Hmmm, indeed. But it seems to occur with the latest 1.8.

I tried some of the patches mentioned on the page on my ruby-1.8.6, and this is
the patch which worked for me (saves me some time before upgrading to 1.8.7).

-S.

--- parse.old.y 2008-08-20 10:59:56.000000000 +0000
+++ parse.y 2008-08-20 11:08:16.000000000 +0000
@@ -5716,7 +5716,7 @@
rb_mem_clear(vars+i, len-i);
}
else {
- *vars++ = (VALUE)ruby_scope;
+ *vars++ = 0;
rb_mem_clear(vars, len);
}
ruby_scope->local_vars = vars;
@@ -5732,6 +5732,7 @@
if (!(ruby_scope->flags & SCOPE_CLONE))
xfree(ruby_scope->local_tbl);
}
+ ruby_scope->local_vars[-1] = 0; /* no reference needed */
ruby_scope->local_tbl = local_tbl();
}
}

Nobuyoshi Nakada

8/20/2008 8:31:00 PM

0

Hi,

At Wed, 20 Aug 2008 20:19:43 +0900,
Sven C. Koehler wrote in [ruby-talk:311956]:
> I tried some of the patches mentioned on the page on my ruby-1.8.6, and this is
> the patch which worked for me (saves me some time before upgrading to 1.8.7).

It has been applied to the latest 1.8, of course.

--
Nobu Nakada

dbd

3/28/2010 12:02:00 AM

0

Hatunen <hatunen@cox.net> wrote:
>Faculty, college...
>
>What's in a name?

Various prickly thorns.

Dave "I hath it on good authority" DeLaney
--
\/David DeLaney posting from dbd@vic.com "It's not the pot that grows the flower
It's not the clock that slows the hour The definition's plain for anyone to see
Love is all it takes to make a family" - R&P. VISUALIZE HAPPYNET VRbeable<BLINK>
http://www.vic... - net.legends FAQ & Magic / I WUV you in all CAPS! --K.