Huge pages on PPC64

[Thomas Stüfe]

Hi Gustavo,

On Mon, Oct 31, 2016 at 1:00 PM, Gustavo Romero <gromero at linux.vnet.ibm.com>
wrote:

> Hi Thomas,
>
> On 28-10-2016 07:36, Thomas Stüfe wrote:
> > Hi guys,
> >
> > On Fri, Oct 28, 2016 at 9:39 AM, Volker Simonis <
> volker.simonis at gmail.com>
> > wrote:
> >
> >> Hi Gustavo,
> >>
> >> please find my comments inline:
> >>
> >> On Thu, Oct 27, 2016 at 11:12 PM, Gustavo Romero
> >> <gromero at linux.vnet.ibm.com> wrote:
> >>> Hi Volker,
> >>>
> >>> On 25-10-2016 05:13, Volker Simonis wrote:
> >>>> Just a quick question: do you also get the same warnings if you are
> >>>> running without compressed oops (i.e. -XX:-UseCompressedClassPointers
> >>>> -XX:-UseCompressedOops)? If not maybe this is related to the fact that
> >>>> for compressed oops we try to allocate memory in low memory regions.
> >>>
> >>> $ java -XX:+PrintCommandLineFlags -Xms256m -Xmx256m -XX:+UseLargePages
> >> -XX:-UseCompressedClassPointers -XX:-UseCompressedOops StrictMath_cos
> >>> -XX:InitialHeapSize=268435456 -XX:MaxHeapSize=268435456
> >> -XX:+PrintCommandLineFlags -XX:-UseCompressedClassPointers
> >> -XX:-UseCompressedOops -XX:+UseLargePages -XX:+UseParallelGC
> >>> OpenJDK 64-Bit Server VM warning: Failed to reserve large pages memory
> >> req_addr: 0x0000000000000000 bytes: 268435456 (errno = 16).
> >>> 0.1709843554185943
> >>>
> >>> It fails when trying to allocate 256 MiB starting at 0x0, so definitely
> >> a low
> >>> memory region.
> >
> >
> > Just a quick pipe-in, req_addr=NULL means "attach to any address, no
> > preference", so this has nothing to do with attaching to low memory
> regions.
>
> ah, kk.
>
> One curious thing is that packaged java (I tested Debian [1] and Ubuntu
> [2])
> seems to try no specific address (NULL), while my jdk8u release build [3]
> seems
> to request one specifically. So on packaged java
>
> (Packaged java, just like my previous paste)
> $ java  -XX:+PrintCommandLineFlags -Xms256m -Xmx256m -XX:+UseLargePages
> -XX:-UseCompressedClassPointers -XX:-UseCompressedOops StrictMath_cos
> -XX:InitialHeapSize=268435456 -XX:MaxHeapSize=268435456
> -XX:+PrintCommandLineFlags -XX:-UseCompressedClassPointers
> -XX:-UseCompressedOops -XX:+UseLargePages -XX:+UseParallelGC
> OpenJDK 64-Bit Server VM warning: Failed to reserve large pages memory
> req_addr: 0x0000000000000000 bytes: 268435456 (errno = 16).
> 0.1709843554185943
>
> but on my build
>
> (jdk8u release build [3])
> $ ./build/linux-ppc64-normal-server-release/jdk/bin/java
> -XX:+PrintCommandLineFlags -Xms256m -Xmx256m -XX:+UseLargePages -XX:-UseCompressedClassPointers
> -XX:-UseCompressedOops StrictMath_cos
> -XX:InitialHeapSize=268435456 -XX:MaxHeapSize=268435456
> -XX:+PrintCommandLineFlags -XX:-UseCompressedClassPointers
> -XX:-UseCompressedOops -XX:+UseLargePages -XX:+UseParallelGC
> OpenJDK 64-Bit Server VM warning: Failed to reserve large pages memory
> req_addr: 0x00003fff86000000 bytes: 268435456 (errno = 16).
>  0.1709843554185943
>
>
I believe we introduced or at least improved coops-friendly heap allocation
for ppc with http://hg.openjdk.java.net/jdk9/hs/hotspot/rev/fee07a43d038

Kind Regards, Thomas

Huge Pages configuration is like this:
> $ fgrep Huge /proc/meminfo
> AnonHugePages:     16384 kB
> HugePages_Total:    1024
> HugePages_Free:     1024
> HugePages_Rsvd:        0
> HugePages_Surp:        0
> Hugepagesize:      16384 kB
>
> Anyway, I believe that the crucial point is if HP is really used optimally
> by
> the JVM when these warnings pop up as there is, as far as I understand, a
> fallback mechanism that will select alternative ways to request an
> allocation
> with Huge Pages (i.e. after mmap() + MAP_HUGETLB fails, it tries shmget() +
> SHM_HUGETLB).
>
> Thank you!
>
> Regards,
> Gustavo
>
>
> [1] Debian
> openjdk version "1.8.0_111"
> OpenJDK Runtime Environment (build 1.8.0_111-8u111-b14-2-b14)
> OpenJDK 64-Bit Server VM (build 25.111-b14, mixed mode)
>
> [2] Ubuntu 16.04
> openjdk version "1.8.0_45"
> OpenJDK Runtime Environment (build 1.8.0_45-b13)
> OpenJDK 64-Bit Server VM (build 25.45-b02, mixed mode)
>
> [3] My local build
> http://hg.openjdk.java.net/jdk8u/jdk8u, d15b51f1149b tip
> openjdk version "1.8.0-internal"
> OpenJDK Runtime Environment (build 1.8.0-internal-gromero_2016_
> 10_30_19_15-b00)
> OpenJDK 64-Bit Server VM (build 25.71-b00, mixed mode)
>
>
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