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

[Stefan Karlsson]

Thanks Coleen, Zhengyu, and Erik for reviewing! This has now been pushed.

Thanks,
StefanK

On 2018-02-15 15:05, 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