Make sure arenas don't allocate bigger than HUGE_PAGE

[bugadani]

Right now, arenas allocate based on the size of the last chunk. It is possible for a grow call to allocate a chunk that is not a multiple of PAGE, and this size is doubled for each subsequent allocation. This means, instead of HUGE_PAGE, the biggest page possible is actually unknown.

This change fixes this, and also removes an unnecessary checked multiplication. It is still possible to allocate bigger than HUGE_PAGE pages, but this will only happen as many times as absolutely necessary.

[rust-highfive]

r? @lcnr

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[lcnr]

Do you expect this changes to have an influence on perf?

[bugadani]

Hard to say, I lean on "not really". Shouldn't degrade perf, at least.

[lcnr]

this code is really hot, so it's better to be safe here

@bors try @rust-timer queue

[rust-timer]

Awaiting bors try build completion

[bors]

⌛ Trying commit 396561b with merge e270068a34bb00af7da331d9029c3b5ce2dad3d3...

[bors]

☀️ Try build successful - checks-actions, checks-azure
Build commit: e270068a34bb00af7da331d9029c3b5ce2dad3d3 (e270068a34bb00af7da331d9029c3b5ce2dad3d3)

[rust-timer]

Queued e270068a34bb00af7da331d9029c3b5ce2dad3d3 with parent ffeeb20, future comparison URL.

[rust-timer]

Finished benchmarking try commit (e270068a34bb00af7da331d9029c3b5ce2dad3d3): comparison url.

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. Please note that if the perf results are neutral, you should likely undo the rollup=never given below by specifying rollup- to bors.

Importantly, though, if the results of this run are non-neutral do not roll this PR up -- it will mask other regressions or improvements in the roll up.

@bors rollup=never

[jyn514]

Looks like no impact.

[lcnr]

well, then

@bors r+ rollup

[bors]

📌 Commit 396561b has been approved by lcnr

[bors]

⌛ Testing commit 396561b with merge 98e1688...

[bors]

☀️ Test successful - checks-actions, checks-azure
Approved by: lcnr
Pushing 98e1688 to master...