How CMS interleave with ParNew

[Srinivas Ramakrishna]

Hi G. Zheng ---


On Wed, Dec 18, 2013 at 11:53 PM, Guoqin Zheng <lanson.zheng at gmail.com>wrote:

> Hey folks,
>
> While search for how CMS works in detail, I happened to an article saying
> usuablly before the inital-mark phase and remark phase, there is young gen
> collection happening and the initial-mark/remark also scan young gen space.
> So
>
>    1. Can you help me understand how the ParNew collection work with CMS
>    to improve the performance.
>
> ParNew collections are minor collections. CMS collects just the old gen
and optionally the perm gen. A concurrent CMS
collection is "interrupted" by ParNew minor collections.

>
>    1.
>    2. Why the young gen space needs to be scanned
>
> Since CMS scans and collects just the old gen and perm gen, it treats the
young gen as a source of roots,
and scans the young gen in its entirety.


>
>    1. If the remark takes very long, what does that mean?
>
> It typically means that there is a lot of concurrent mutation happening in
the old gen (perhaps as a result of
objects being promoted rapidly into the old gen). In this case, the
concurrent scanning and precleaning of the
CMS generation (which is designed to catch up with mutations in the old
gen) isn't able to keep up with
the rate of mutations happening there.


>
>    1. Finally, is there a official/or good docs talking about CMS in
>    detail?
>
>
The paper by Printezis and Detlefs in ISMM 2000 was the starting point of
the
HotSpot CMS implementation, with a few modifications along the way.

HTHS.
-- ramki


> Thanks,
>
> G. Zheng
>
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