RFR(S) 8241004: NMT tests fail on unalinged thread size with debug build

[Zhengyu Gu]

Hi Boris and Thomas,

Thanks for fixing it.

On 5/13/20 2:23 PM, Thomas Stüfe wrote:
> Hi Boris,
> 
> I think this looks good. Zhengyu should look at this to make sure.
> 
> When looking at os::committed_in_range() I remembered that this was a
> rather specific function. Its name suggests that it counts all committed
> pages in a range; but it only counts the first committed contiguous range,
> then stops.

This function was introduced mainly for stack tracking, and it is the 
only use at this moment.

But I have ideas for other cases, e.g. having NMT no tracking committed 
regions, but scanning reserved regions for committed regions. This not 
only eliminates the most of complexity in virtual memory tracking, but 
also yields more accurate information (because os::commit() does not 
actually commit memory).

So, I wonder if it is better solution to leave os::committed_in_range 
alone, but make adjustment in SnapshotThreadStackWalker[1], if it is 
thread stack only problem?

-Zhengyu



[1] 
http://hg.openjdk.java.net/jdk/jdk/file/a44396903fd8/src/hotspot/share/services/virtualMemoryTracker.cpp#l531




> 
> Thanks, Thomas
> 
> 
> 
> On Wed, May 13, 2020 at 6:29 PM Boris Ulasevich <boris.ulasevich at bell-sw.com>
> wrote:
> 
>> Hi Thomas,
>>
>> Good point! Thanks.
>> I reworked the function to ease both restrictions.
>> http://cr.openjdk.java.net/~bulasevich/8241004/webrev.01
>>
>> regards,
>> Boris
>>
>> On 13.05.2020 08:59, Thomas Stüfe wrote:
>>
>> Hi Boris,
>>
>> Note that we have unaligned stack boundaries on AIX too, not so strange :)
>>
>> What I do not like about the solution is that it loosens the restriction
>> on the input size while keeping the restriction on the start address. I'd
>> rather see this function either in its current form (requiring the input
>> ranges to be page aligned) or the input range to be completely
>> unrestricted. This function is currently only used by NMT but it is useful
>> and may be used in other places too.
>>
>> Can you make it work with arbitrary input ranges? I do not think this
>> would require much changes from your patch, you do most of the work already.
>>
>> Thanks!
>>
>> ..Thomas
>>
>>
>>
>> On Thu, May 7, 2020 at 2:56 PM boris <boris.ulasevich at bell-sw.com> wrote:
>>
>>> Hi,
>>>
>>> Please review the following change.
>>>
>>> http://cr.openjdk.java.net/~bulasevich/8241004/webrev.00
>>> http://bugs.openjdk.java.net/browse/JDK-8241004
>>>
>>> The stack size created by the implementation of the pthread library is
>>> not necessarily page aligned. It is weird, but it is not forbidden: the
>>> pthread library may add some gap on it own. My change removes stack size
>>> alignment assert checks and tunes NMT committed range calculation for
>>> the case of unaligned stack size.
>>>
>>> thanks,
>>> Boris
>>>
>>
>>
>