[ruby-core:60106] [ruby-trunk - Feature #9113] Ship Ruby for Linux with jemalloc out-of-the-box

Issue #9113 has been updated by Eric Wong.


 I tried jemalloc 3.5.0 vs eglibc 2.13-38 (Debian x86_64)
 
 http://80x24.org/bmlog-20140126-003136.7320.gz
 
 Mostly close results, but I think our "make benchmark" suite is
 incomplete and we need more fork/concurrency-intensive benchmarks of
 large apps.
 
 io_file_read and vm2_bigarray seem to be big losses because jemalloc
 tends to release large allocations back to the kernel more aggressively
 (and the kernel must zero that memory).
 
 [1] I have applied two patches for improved benchmark consistency:
         https://bugs.ruby-lang.org/issues/5985#change-44442
         https://bugs.ruby-lang.org/issues/9430
     (Note: I still don't trust the vm_thread* benchmarks too much,
      they seem very inconsistent even with no modifications)

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Feature #9113: Ship Ruby for Linux with jemalloc out-of-the-box
https://bugs.ruby-lang.org/issues/9113#change-44604

* Author: Sam Saffron
* Status: Feedback
* Priority: Normal
* Assignee: 
* Category: build
* Target version: 
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libc's malloc is a problem, it fragments badly meaning forks share less memory and is slow compared to tcmalloc or jemalloc. 

both jemalloc and tcmalloc are heavily battle tested and stable. 

2 years ago redis picked up the jemalloc dependency see: http://oldblog.antirez.com/post/everything-about-redis-24.html 

To quote antirez:
``
But an allocator is a serious thing. Since we introduced the specially encoded data types Redis started suffering from fragmentation. We tried different things to fix the problem, but basically the Linux default allocator in glibc sucks really, really hard. 
``

--- 

I recently benched Discourse with tcmalloc / jemalloc and default and noticed 2 very important thing: 

median request time reduce by up to 10% (under both)
PSS (proportional share size) is reduced by 10% under jemalloc and 8% under tcmalloc.

We can always use LD_PRELOAD to yank these in, but my concern is that standard distributions are using a far from optimal memory allocator. It would be awesome if the build, out-of-the-box, just checked if it was on Linux  (eg: https://github.com/antirez/redis/blob/unstable/src/Makefile#L30-L34 ) and then used jemalloc instead. 



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