Hi Sundar, It's described on our project wiki: https://wiki.openjdk.java.net/display/zgc/Main --- Returning Unused Memory to the Operating System By default, ZGC uncommits unused memory, returning it to the operating system. This is useful for applications and environments where memory footprint is a concern. This feature can be disabled using -XX:-ZUncommit. Furthermore, memory will not be uncommitted so that the heap size shrinks below the minimum heap size (-Xms). This means this feature will be implicitly disabled if the minimum heap size (-Xms) is configured to be equal to the maximum heap size (-Xmx). An uncommit delay can be configured using -XX:ZUncommitDelay=<seconds> (default is 300 seconds). This delay specifies for how long memory should have been unused before it's eligible for uncommit. --- Additionally, -Xms sets both -XX:InitialHeapSize and -XX:MinHeapSize, so if you only want to set the lower limit of the amount of committed memory for the heap, you can use -XX:MinHeapSize instead. StefanK On 2019-12-10 19:57, Sundara Mohan M wrote:
Hi, I am using following java version and see Uncommit feature is disabled by default openjdk version "13.0.1" 2019-10-15 OpenJDK Runtime Environment AdoptOpenJDK (build 13.0.1+9) OpenJDK 64-Bit Server VM AdoptOpenJDK (build 13.0.1+9, mixed mode, sharing)
GC logs
[2019-12-10T18:47:43.171+0000][0.007s][info][gc,init] Initializing The Z Garbage Collector [2019-12-10T18:47:43.171+0000][0.007s][info][gc,init] Version: 13.0.1+9 (release) [2019-12-10T18:47:43.171+0000][0.007s][info][gc,init] NUMA Support: Enabled [2019-12-10T18:47:43.171+0000][0.007s][info][gc,init] NUMA Nodes: 2 [2019-12-10T18:47:43.171+0000][0.007s][info][gc,init] CPUs: 48 total, 48 available [2019-12-10T18:47:43.171+0000][0.007s][info][gc,init] Memory: 128318M [2019-12-10T18:47:43.171+0000][0.007s][info][gc,init] Large Page Support: Disabled [2019-12-10T18:47:43.171+0000][0.007s][info][gc,init] Workers: 40 parallel, 7 concurrent [2019-12-10T18:47:43.174+0000][0.010s][info][gc,init] Address Space: 0x0000040000000000 - 0x0000140000000000 (16T) [2019-12-10T18:47:43.174+0000][0.010s][info][gc,init] Heap backed by file: /tmp/java_heap.112273 [2019-12-10T18:47:43.174+0000][0.010s][info][gc,init] Min Capacity: 80000M [2019-12-10T18:47:43.174+0000][0.010s][info][gc,init] Initial Capacity: 80000M [2019-12-10T18:47:43.174+0000][0.010s][info][gc,init] Max Capacity: 80000M [2019-12-10T18:47:43.174+0000][0.010s][info][gc,init] Max Reserve: 112M [2019-12-10T18:47:43.174+0000][0.010s][info][gc,init] Pre-touch: Enabled [2019-12-10T18:47:43.174+0000][0.010s][info][gc,init] Available space on backing filesystem: 125929M *[2019-12-10T18:48:30.290+0000][47.126s][info][gc,init] Uncommit: Disabled* [2019-12-10T18:49:30.315+0000][107.151s][info][gc,init] Runtime Workers: 40 parallel [2019-12-10T18:49:30.318+0000][107.155s][info][gc ] Using The Z Garbage Collector ... Is this feature enabled by default in later release only?
Thanks Sundar