On Mon, 22 Feb 2021 05:53:19 GMT, Ralf Schmelter <rschmel...@openjdk.org> wrote:
>> Lin Zang has updated the pull request incrementally with one additional >> commit since the last revision: >> >> fix build fail issue on windows > > Hi, > > I've benchmarked the code on my machine (128GB memory, 56 logical CPUs) with > an example creating a 32 GB heap dump. I only saw a 10 percent reduction in > time, both using uncompressed and compressed dumps. Have you seen better > numbers in your benchmarks? > > And it seems to potentially use a lot more temporary memory. In my example I > had a 4 GB array in the heap and the new code allocated 4 GB of additional > memory to write this array. This could happen in more threads in parallel, > increasing the memory consumption even more. > > If the above problems could be fixed, I would suggest to just use the > parallel code in all cases. Hi @schmelter-sap, Thanks a lot for reviewing and benchmarking. > I've benchmarked the code on my machine (128GB memory, 56 logical CPUs) with > an example creating a 32 GB heap dump. I only saw a 10 percent reduction in > time, both using uncompressed and compressed dumps. Have you seen better > numbers in your benchmarks? > > And it seems to potentially use a lot more temporary memory. In my example I > had a 4 GB array in the heap and the new code allocated 4 GB of additional > memory to write this array. This could happen in more threads in parallel, > increasing the memory consumption even more. I have done some preliminary test on my machine (16GB, 8 core), the data are shown as follow: `$ jmap -dump:file=dump4.bin,parallel=4 127420` `Dumping heap to /home/lzang1/Source/jdk/dump4.bin ...` `Heap dump file created [932950649 bytes in 0.591 secs]` `$ jmap -dump:file=dump1.bin,parallel=1 127420` `Dumping heap to /home/lzang1/Source/jdk/dump1.bin ...` `Heap dump file created [932950739 bytes in 2.957 secs]` But I do have observed unstable data reported on a machine with more cores and larger RAM, plus a workload with more heap usage. I thought that may be related with the memory consumption as you mentioned. And I am investigating the way to optimize it. > If the above problems could be fixed, I would suggest to just use the > parallel code in all cases. Thanks a lot! I will let you know when I make some progress on optimization. ------------- PR: https://git.openjdk.java.net/jdk/pull/2261
