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

Poonam Bajaj poonam.bajaj at
Mon Mar 14 23:41:37 PDT 2011

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 ?


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: 
> 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
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Poonam Bajaj | Staff Engineer
Phone: +66937451 <tel:+66937451> | Mobile: +9844511366 <tel:+9844511366>
JVM Sustaining Engineering
| Bangalore
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