From: dennisb55@...
Date: 2018-05-16T05:03:33+00:00
Subject: [ruby-core:87059] [Ruby trunk Feature#14759] [PATCH] set	M_ARENA_MAX for glibc malloc

Issue #14759 has been updated by bluz71 (Dennis B).


normalperson (Eric Wong) wrote:

> Personally, I prefer using M_ARENA_MAX=1 (via MALLOC_ARENA_MAX
> env) myself, but there is currently a performance penalty for
> that.
> 
> 
> gc.c (Init_GC): set M_ARENA_MAX=2 for glibc malloc

This is not desirable in the longer term.

CRuby will likely get true concurrency in the future via ko1's Guild proposal. Reducing arenas will create new contention and serialisation at the memory allocator level thus negating the full benefits of Guilds.

Debate is currently occurring in [feature $14718](https://bugs.ruby-lang.org/issues/14718) about using jemalloc to solve Ruby's memory fragmentation issue on Linux. Resolution of that (one way or the other) should inform what to do here.

I believe this should be paused until #14718 is clarified.



----------------------------------------
Feature #14759: [PATCH] set M_ARENA_MAX for glibc malloc
https://bugs.ruby-lang.org/issues/14759#change-72019

* Author: normalperson (Eric Wong)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
Not everybody benefits from jemalloc and the extra download+install
time is not always worth it.  Lets make the user experience for
glibc malloc users better, too.

Personally, I prefer using M_ARENA_MAX=1 (via MALLOC_ARENA_MAX
env) myself, but there is currently a performance penalty for
that.


gc.c (Init_GC): set M_ARENA_MAX=2 for glibc malloc

glibc malloc creates too many arenas and leads to fragmentation.
Given the existence of the GVL, clamping to two arenas seems
to be a reasonable trade-off for performance and memory usage.

Some users (including myself for several years, now) prefer only
one arena, now, so continue to respect users' wishes when
MALLOC_ARENA_MAX is set.

Thanks to Mike Perham for the reminder [ruby-core:86843]


This doesn't seem to conflict with jemalloc, so it should be safe
for all glibc-using systems.


---Files--------------------------------
0001-gc.c-Init_GC-set-M_ARENA_MAX-2-for-glibc-malloc.patch (1.46 KB)


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