RFR: 8196405: [REDO] NMT: add_committed_regions doesn't merge succeeding regions
Zhengyu Gu
zgu at redhat.com
Thu Feb 15 16:23:42 UTC 2018
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
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