Request for review (S): 6627787, 6896099, 7000125: CMS heap sizing (1 RFE, 2 Bugs)

[Poonam Bajaj]

Hi Ramki,

Thanks for improving the GC logging with these changes.

What is the reason behind choosing 16M for sparc and 64M for x86 systems 
as the default value for CMSYoungGenPerWorker ?

Thanks,
Poonam

On 3/15/2011 7:37 AM, Y. Srinivas Ramakrishna wrote:
> (bug) 6627787: CMS: JVM refuses to start up with -Xms16m -Xmx16m
> (RFE) 6896099: Integrate CMS heap ergo with default heap sizing ergo
> (bug) 7000125: CMS: Anti-monotone young gen sizing with respect to 
> maximum whole heap size specification
>
> Problem: CMS heap sizing does not make use of server/client heap sizing
> ergo, mainly because it wants to keep maximum gc pauses somewhat
> under control rather than necessarily sizing for throughput.
> There have been many changes and small tweaks over the years
> in this code and it has collected a lot of unnecessary settings
> which also conflict with the sizing decisions being made
> elsewhere in the heap sizing/policy subsystem, resulting,
> for example, in the two bugs in the list of CR's above.
>
> Solution: Allow CMS to make use of server/client heap sizing
> ergonomics, just like all the other collectors, while keeping the
> young generation small enough so as to keep pause times
> reasonable. One of these required a CPU-specific default.
> Jettison old settings and flags specific to use in JDK 6
> to preserve JDK 5 like CMS settings, which are now considered
> quite obsolete.
>
> Since the fixes for the two defects and the one RFE were
> entangled, it made sense to fix them all in one changeset.
>
> Testing: internal reference workloads to assess the changes
> from current settings, and to ensure that gc pauses are
> still "reasonable" with the newer default settings.
> The command-lines in the two bugs to verify that the
> sizing anomalies are no longer present.
>
> Webrev: 
> http://cr.openjdk.java.net/~ysr/6627787_6896099_7000125/webrev.01/
>
> This contains changes following one internal review (thanks Bengt 
> Rutisson!),
> but if anyone else has further feedback, please let me know.
>
> thanks!
> -- ramki

-- 
Best regards, Poonam

Sun, an Oracle company
Sun, an Oracle Company
Poonam Bajaj | Staff Engineer
Phone: +66937451 <tel:+66937451> | Mobile: +9844511366 <tel:+9844511366>
JVM Sustaining Engineering
| Bangalore
Green Oracle <http://www.oracle.com/commitment> Oracle is committed to 
developing practices and products that help protect the environment

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