[15] RFR: 8236595: Add more comments about how to setup simulated NVRAM before run java/nio/MappedByteBuffer/PmemTest.java

[Chris Yin]

Thank you, Alan. Sure, I will wait to see if any comments/suggestions from Andrew.

Thanks,
Chris

> On 3 Jan 2020, at 1:49 AM, Alan Bateman <Alan.Bateman at oracle.com> wrote:
> 
> Looks okay to me but probably best if Andrew Dinn reviews (as the test is part of JEP 352).
> 
> -Alan
> 
> On 31/12/2019 05:18, Chris Yin wrote:
>> Please have a review for below comments change only to manual test java/nio/MappedByteBuffer/PmemTest.java, the motivation is to make the pre-config steps for setup simulated NVRAM device more clear to newbie, thanks
>> 
>> JBS Issue: https://bugs.openjdk.java.net/browse/JDK-8236595
>> Webrev: http://cr.openjdk.java.net/~xyin/8236595/webrev.00/
>> 
>> 
>> Patch:
>> --- old/test/jdk/java/nio/MappedByteBuffer/PmemTest.java	2019-12-31 12:47:34.000000000 +0800
>> +++ new/test/jdk/java/nio/MappedByteBuffer/PmemTest.java	2019-12-31 12:47:34.000000000 +0800
>> @@ -50,10 +50,20 @@
>>   *
>>   * https://developers.redhat.com/blog/2016/12/05/configuring-and-using-persistent-memory-rhel-7-3/
>>   * https://nvdimm.wiki.kernel.org/
>> - * TL;DR: add "memmap=1G!4G" to /etc/default/grub,
>> - *        then grub2-mkconfig -o /boot/grub2/grub.cfg and reboot
>> + * TL;DR: add "memmap=1G!4G" to /etc/default/grub, eg. GRUB_CMDLINE_LINUX="memmap=1G!4G"
>> + *        then ("sudo" may required)
>> + *          for RHEL(BIOS-based): grub2-mkconfig -o /boot/grub2/grub.cfg
>> + *          for RHEL(UEFI-based): grub2-mkconfig -o /boot/efi/EFI/redhat/grub.cfg
>> + *          for Ubuntu: update-grub2
>> + *        finally reboot
>> + *        after the host been rebooted, a new /dev/pmem{N} device should exist,
>> + *        naming conversion starts at /dev/pmem0
>> + *
>> + *  Prepare test directory follow below commands, "sudo" may required
>> + *  (if ndctl or mkfs.xfs not exist, install ndctl or xfsprogs package first)
>> + *  (for RHEL8, when call mkfs.xfs, specify the -m reflink=0 option to disable reflink feature)
>>   *
>> - *  ndctl create-namespace  * -f -e namespace0.0 -m memory -M mem
>> + *  ndctl create-namespace -f -e namespace0.0 -m memory -M mem
>>   *  mkdir /mnt/pmem
>>   *  mkfs.xfs -f /dev/pmem0; mount -o dax /dev/pmem0 /mnt/pmem/
>>   *  mkdir /mnt/pmem/test; chmod a+rwx /mnt/pmem/test
>> 
>> Regards,
>> Chris
>> 
>