RFR: 8196405: [REDO] NMT: add_committed_regions doesn't merge succeeding regions

[Stefan Karlsson]

Thanks for reviewing!

StefanK

On 2018-02-15 17:23, Zhengyu Gu wrote:
> Looks really good.
>
> Thanks for fixing it.
>
> -Zhengyu
>
> On 02/15/2018 09:05 AM, Stefan Karlsson wrote:
>> Hi all,
>>
>> Please review this patch to fix the merging of committed regions in 
>> NMT's VirtualMemoryTracker.
>>
>> http://cr.openjdk.java.net/~stefank/8196405/webrev.01/
>> https://bugs.openjdk.java.net/browse/JDK-8196405
>>
>> The previous attempt to fix this didn't deal with overlapping 
>> committed regions correctly. This patch solves that case by first 
>> removing regions, and parts of regions, that intersect with the newly 
>> committed region. After that, the new region can be added and/or 
>> merged with any adjacent regions.
>>
>> There used to be a special-case for code paths that both reserve and 
>> commit memory at the same time. ReservedMemoryRegion had an 
>> all_committed boolean to track that state, and subsequent commits in 
>> the reserved region were ignored. There were a number of bugs cause 
>> by this special-handeling, when regions were committed or uncommitted 
>> inside an all_committed region. This patch removes the all_committed 
>> property and instead queries the _committed_regions list where 
>> necessary.
>>
>> The patch removes special case handling for mtThreadStacks. The 
>> intention is that the add_committed_region and 
>> remove_uncomitted_region functions should be correct, so that we 
>> don't need that kind of special-case handling.
>>
>> The overlap_region function uses 'sz - 1', which would be broken if 
>> sz ever was 0. I added asserts to check for this.
>>
>> I've added a small jtreg test for the initial problem that this bug 
>> report was intending to fix. But I realized that the WhiteBox API 
>> didn't support setting up and testing different call stacks for the 
>> memory reservations and commits, so I introduced a C++ gtest. This 
>> test is both faster to execute, easier to debug, and more flexible, 
>> so I hope this is appreciated. :)
>>
>> I've tested this with the added unit tests, short run with 
>> Kitchensink, and mach5 hs-tier1,hs-tier2. Anything else that I should 
>> be running?
>>
>> While working on this I found two other bugs:
>>
>>   https://bugs.openjdk.java.net/browse/JDK-8198225
>>   os::attempt_reserve_memory_at records memory as committed
>>
>>   https://bugs.openjdk.java.net/browse/JDK-8198226
>>   os::attempt_reserve_memory_at records reserved memory twice on windows
>>
>> Thanks,
>> StefanK