25 messages in net.java.openjdk.hotspot-gc-devRe: Free ratio based heap shrinking i...| From | Sent On | Attachments |
|---|---|---|
| Hiroshi Yamauchi | Mar 10, 2010 3:16 pm | |
| Jon Masamitsu | Mar 10, 2010 4:03 pm | |
| Jon Masamitsu | Mar 10, 2010 11:05 pm | |
| Hiroshi Yamauchi | Mar 11, 2010 3:08 pm | |
| Jon Masamitsu | Mar 15, 2010 12:03 pm | |
| Hiroshi Yamauchi | Mar 15, 2010 4:49 pm | |
| Jon Masamitsu | Mar 16, 2010 3:38 pm | |
| Jon Masamitsu | Mar 16, 2010 8:03 pm | |
| Hiroshi Yamauchi | Mar 18, 2010 11:27 am | |
| Hiroshi Yamauchi | Mar 18, 2010 12:01 pm | |
| Jon Masamitsu | Mar 19, 2010 10:03 am | |
| Hiroshi Yamauchi | Mar 24, 2010 5:00 pm | |
| Jon Masamitsu | Mar 26, 2010 4:54 pm | |
| Hiroshi Yamauchi | Mar 31, 2010 11:25 am | |
| Jon Masamitsu | Apr 1, 2010 9:02 am | |
| Hiroshi Yamauchi | Apr 13, 2010 11:20 am | |
| Hiroshi Yamauchi | Apr 28, 2010 1:36 pm | |
| Jon Masamitsu | Apr 29, 2010 1:57 pm | |
| Hiroshi Yamauchi | Apr 29, 2010 2:47 pm | |
| Jon Masamitsu | May 3, 2010 10:52 am | |
| Hiroshi Yamauchi | May 10, 2010 4:50 pm | |
| Jon Masamitsu | May 13, 2010 8:52 am | |
| Hiroshi Yamauchi | May 13, 2010 4:34 pm | |
| Jon Masamitsu | May 13, 2010 10:42 pm | |
| Hiroshi Yamauchi | May 17, 2010 5:26 pm |
| Subject: | Re: Free ratio based heap shrinking in the parallel collector | |
|---|---|---|
| From: | Hiroshi Yamauchi (yama...@google.com) | |
| Date: | Mar 24, 2010 5:00:55 pm | |
| List: | net.java.openjdk.hotspot-gc-dev | |
Hi Jon,
You're right that adjust_for_throughput() will not shrink the heap.
Another part of the policy is that the heap is shrunk if the throughput goal and the pause time goal are being met. It's a slower process than just enforcing MaxHeapFreeRatio and requires a number of GC's (that is, the heap would be shrunk down a percentage at each GC).
GC usually happens only as needed. So, after the application goes idle, GC does not probably happen. The next GC happens only after the application goes active again. Assuming that, there aren't many chances to shrink the heap (maybe only one). If the application calls System.gc() right before going idle, that may be the only chance. In such cases, the slower process may not work very well.
We would need to change the UseAdaptiveSizePolicy to do something like
if ( average-pause > pause-goal) shrink heap else if (average-throughput < throughput-goal) && ! (UseFreeRatioForParallelGC && heap too empty)) <<<< new grow heap else shrink heap
Or maybe something like
if ( average-pause > pause-goal) shrink heap else if (average-throughput < throughput-goal) if (UseFreeRatioForParallelGC && heap too empty) <<<< new shrink heap (policy-to-be-determined) <<<< else <<<< grow heap else if (average-throughput < throughput-goal) grow heap to reduce gc overhead else shrink heap
OK. I think the latter may be able to shrink the heap more aggressively.
Do you think the free ratio-based shrinking should happen only when the throughput goal is met? Using the above scenario, when the application is working hard (and perhaps GC is working hard as well) and goes idle next moment, the average throughput at the time of the phase change may not be good enough for the goal to be met (hence no shrinking).
Thanks, Hiroshi