RFR: 8315548: G1: Document why VM_G1CollectForAllocation::doit() may allocate without completing a GC

[Thomas Schatzl]

On Mon, 4 Sep 2023 12:47:43 GMT, Ivan Walulya <iwalulya at openjdk.org> wrote:

> Hi all,
> 
> Please review this trivial change to add a comment explaining why we attempt to allocate at a VM_G1CollectForAllocation safepoint before triggering garbage collection.
> 
> Thanks,
> Ivan

Lgtm and trivial. Feel free to ignore my comments.

src/hotspot/share/gc/g1/g1VMOperations.cpp line 133:

> 131:     // GCLocker, potentially leading to expansion of the Eden space by other mutators.
> 132:     // If the Eden space was expanded, the allocation request might succeed without
> 133:     // triggering a garbage collection.

Suggestion:

    // During the execution of this VM operation, there may have been a concurrent active
    // GCLocker, potentially leading to expansion of the Eden space by other mutators.
    // If the Eden space were expanded, this allocation request might succeed without
    // the need for triggering a garbage collection.

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Marked as reviewed by tschatzl (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/15559#pullrequestreview-1609627461
PR Review Comment: https://git.openjdk.org/jdk/pull/15559#discussion_r1314995363