Michał Chojnowski 1c1741cfbc logalloc_test: don't test performance in test background_reclaim ...

The test is failing in CI sometimes due to performance reasons.

There are at least two problems:
1. The initial 500ms (wall time) sleep might be too short. If the reclaimer
   doesn't manage to evict enough memory during this time, the test will fail.
2. During the 100ms (thread CPU time) window given by the test to background
   reclaim, the `background_reclaim` scheduling group isn't actually
   guaranteed to get any CPU, regardless of shares. If the process is
   switched out inside the `background_reclaim` group, it might
   accumulate so much vruntime that it won't get any more CPU again
   for a long time.

We have seen both.

This kind of timing test can't be run reliably on overcommitted machines
without modifying the Seastar scheduler to support that (by e.g. using
thread clock instead of wall time clock in the scheduler), and that would
require an amount of effort disproportionate to the value of the test.

So for now, to unflake the test, this patch removes the performance test
part. (And the tradeoff is a weakening of the test).

2025-05-06 18:59:18 +02:00

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