[12] RFR(S): 8208277: Code cache heap (-XX:ReservedCodeCacheSize) doesn't work with 1GB LargePages

[Vladimir Kozlov]

Looks reasonable.

Did you tested Segmented CodeCache and huge pages if you use 8Gb size?

Thanks,
Vladimir

On 12/4/18 8:34 AM, Tobias Hartmann wrote:
> Hi,
> 
> please review the following patch:
> https://bugs.openjdk.java.net/browse/JDK-8208277
> http://cr.openjdk.java.net/~thartmann/8208277/webrev.00/
> 
> The code cache does not use 1GB pages even if the InitialCodeCacheSize is set to 1GB. The reason for
> this is the logic in CodeCache::page_size which sets the page size such that the code cache contains
> at least 8 pages to allow for an incremental commit of memory (otherwise, with a 1GB code cache and
> 1GB pages, all the memory would be committed right from the beginning).
> 
> I've fixed this by setting the minimum number of pages to 1 if ReservedCodeCacheSize is equal to
> InitialCodeCacheSize. I've also disabled code cache segmentation if the code cache does not at least
> contain 8 pages because segmentation would otherwise disable the advantage of huge pages.
> 
> Without my fix, only one 1GB page is used for the Java heap:
> 
> -sh-4.1# base/jdk-12/fastdebug/bin/java -Xmx1g -Xms1g -XX:+AlwaysPreTouch -XX:+UseG1GC
> -XX:+UseLargePages -XX:ReservedCodeCacheSize=1G -XX:InitialCodeCacheSize=1G Test &
> [1] 1961
> -sh-4.1# grep huge /proc/*/numa_maps
> /proc/1961/numa_maps:c0000000 default file=/anon_hugepage\040(deleted) huge anon=1 dirty=1 N0=1
> -sh-4.1# grep Huge /proc/meminfo
> HugePages_Total:      20
> HugePages_Free:       19
> HugePages_Rsvd:        0
> HugePages_Surp:        0
> Hugepagesize:    1048576 kB
> 
> With my fix, two 1GB pages are used (one for the heap and one for the code cache):
> 
> -sh-4.1# fix/jdk-12/fastdebug/bin/java -Xmx1g -Xms1g -XX:+AlwaysPreTouch -XX:+UseG1GC
> -XX:+UseLargePages -XX:ReservedCodeCacheSize=1G -XX:InitialCodeCacheSize=1G Test &[1] 13813
> -sh-4.1# grep huge /proc/*/numa_maps
> /proc/13813/numa_maps:c0000000 default file=/anon_hugepage\040(deleted) huge anon=1 dirty=1 N0=1
> /proc/13813/numa_maps:7f3400000000 default file=/anon_hugepage\040(deleted) huge anon=1 dirty=1 N0=1
> -sh-4.1# grep Huge /proc/meminfo
> HugePages_Total:      20
> HugePages_Free:       18
> HugePages_Rsvd:        0
> HugePages_Surp:        0
> Hugepagesize:    1048576 kB
> 
> If InitialCodeCacheSize is set to the default, the code cache will not use 1GB pages to allow
> incremental committing of memory.
> 
> Thanks,
> Tobias
>