On Wed, 29 Jan 2025 19:20:34 GMT, Jorn Vernee <jver...@openjdk.org> wrote:
>> Currently, to free the memory allocated in a confined arena, we keep track >> of a list of 'cleanup actions', stored in linked list format in a so-called >> `ResourceList`, attached to the scope of the arena. When the scope is >> closed, we loop over all the entries in this resource list, and run all the >> cleanup actions one by one. >> >> However, due to this linked list format, plus the control flow introduced by >> the cleanup loop, C2's escape analysis can not keep track of the nodes of >> this linked list (`ResourceList.ResourceCleanup`), and as a result, they can >> not be scalar replaced. >> >> We can prevent just the first `ResourceCleanup` instance from escaping, by >> pulling out the first element of the list into a separate field. I also >> tried a setup where I had 2 separate fields for the first 2 elements, as >> well as a setup with an array with a fixed set of elements. While these also >> worked to prevent the first node from escaping, they were not able to >> provide the same benefit for multiple resource cleanup instances. >> Nevertheless, avoiding the allocation of the first element is relatively >> simple, and seems like a low-hanging fruit. >> >> I've changed the `AllocTest` benchmark a bit so that we don't return the >> `MemorySegment` in `alloc_confined`, which would make it always escape. That >> way, we can use this existing benchmark to test whether there are any >> allocations when calling `allocate` on a confined arena. This matches what >> we were doing in the other benchmark methods in the same class. > > Jorn Vernee has updated the pull request with a new target base due to a > merge or a rebase. The incremental webrev excludes the unrelated changes > brought in by the merge/rebase. The pull request contains seven additional > commits since the last revision: > > - update copyright year > - Merge branch 'master' into NoEscape > - polish v2 > - simplify benchmark > - polish > - One element cache > - fix bench Marked as reviewed by liach (Reviewer). ------------- PR Review: https://git.openjdk.org/jdk/pull/23321#pullrequestreview-2582133422
