Feature #3322: Simple Patch to make ruby copy-on-write-friendly

• Status: Rejected
• Assignee: authorNari (Narihiro Nakamura)
• Target version: -

[Dan42 (Daniel DeLorme)]

=begin
A lot has been said about ruby's lack of COW-friendliness; a full solution like REE has a performance impact, but I think I've come up with a simple trick that solves the problem of pre-forking servers. Basically, this patch implements GC.leak which marks all existing objects as ineligible for GC, and existing heaps as ineligible for allocation of new objects. It may sound hacky, but it's exactly the point of pre-forking in most cases: load a bunch of code & data and then keep it in memory forever.

Compare the memory usage of these:
./ruby -e 'x=(1..40_000_000).map{""}; Process.fork; x=[]; GC.start; sleep 10'
./ruby -e 'x=(1..40_000_000).map{""}; GC.leak; Process.fork; x=[]; GC.start; sleep 10'

This patch has the advantage of being

1. simple
2. free of negative performance impact
3. implemented and available now

PS: As far as I can tell the patch works fine, but I'm not terribly well-versed about the innards of ruby so I'd appreciate some code review. Thanks.
=end

[rkh (Konstantin Haase)]

=begin
You might want to run the GC first.
=end

[Dan42 (Daniel DeLorme)]

• File cow2.patch cow2.patch added

=begin
Adding garbage_collect() before leak and after unleak
=end

[rogerdpack (Roger Pack)]

=begin
Good idea. Unfortunately it needs to traverse (and mark) all the "old" heaps during GC, so that it can see which items are still accessible in the namespace. Unless you can guarantee that no new objects will be pointed to by members of the old heap, you still have to traverse everything. At least AFAIK.
-rp
=end

[akr (Akira Tanaka)]

• Project changed from Ruby to Ruby master
• Category changed from core to core

[nahi (Hiroshi Nakamura)]

• Description updated (diff)
• Assignee set to authorNari (Narihiro Nakamura)

[shyouhei (Shyouhei Urabe)]

• Status changed from Open to Assigned

[authorNari (Narihiro Nakamura)]

• Status changed from Assigned to Rejected
• % Done changed from 0 to 100

Sorry for the late relpy.
We already have Bitmap Marking GC in Ruby2.0 so I reject it.

Thanks.