Consider the following code snippet:
```c++
future<> foo() {
semaphore.consume(1024);
}
future<> bar() {
return _allocating_section([&] {
foo();
});
}
```
If the consumed memory triggers the OOM kill limit, the semaphore will throw `std::bad_alloc`. The allocating section will catch this, bump std reserves and retry the lambda. Bumping the reserves will not do anything to prevent the next call to `consume()` from triggering the kill limit. So this cycle will repeat until std reserves are so large that ensuring the reserve fails. At this point LSA gives up and re-throws the `std::bad_alloc`. Beyond the useless time spent on code that is doomed to fail, this also results in expensive LSA compaction and eviction of the cache (while trying to ensure reserves).
Prevent this situation by throwing a distinct exception type which is derived from `std::bad_alloc`. Allocating section will not retry on seeing this exception.
A test reproducing the bug is also added.
Fixes: #15278Closesscylladb/scylladb#15581
* github.com:scylladb/scylladb:
test/boost/row_cache_test: add test_cache_reader_semaphore_oom_kill
utils/logalloc: handle utils::memory_limit_reached in with_reclaiming_disabled()
reader_concurrency_semaphore: use utils::memory_limit_reached exception
utils: add memory_limit_reached exception
e600f35d1e