The config variable `components_memory_reclaim_threshold` limits the
memory available to the sstable bloom filters. Any change to its value
is not immediately propagated to the sstable manager, despite it being
a LiveUpdate variable. The updated value takes effect only when a new
sstable is created or deleted.
This PR first refactors the reclaim and reload logic into a single
background fiber. It then updates the sstable manager to subscribe to
changes in the `components_memory_reclaim_threshold` configuration value
and immediately triggers the reclaim/reload fiber when a change is
detected.
Fixes#21947
This is an improvement and does not need to be backported.
Closesscylladb/scylladb#22725
* github.com:scylladb/scylladb:
sstables_manager: trigger reclaim/reload on `components_memory_reclaim_threshold` update
sstables_manager: maybe_reclaim_components: yield between iterations
sstables_manager: rename `increment_total_reclaimable_memory_and_maybe_reclaim()`
sstables_manager: move reclaim logic into `components_reclaim_reload_fiber()`
sstables_manager: rename `_sstable_deleted_event` condition variable
sstables_manager: rename `components_reloader_fiber()`
sstables_manager: fix `maybe_reclaim_components()` indentation
sstables_manager: reclaim components memory until usage falls below threshold
sstables_manager: introduce `get_components_memory_reclaim_threshold()`
sstables_manager: extract `maybe_reclaim_components()`
sstables_manager: fix `maybe_reload_components()` indentation
sstables_manager: extract out `maybe_reload_components()`
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