DAOS-16896 common: Spill Over Evictable Buckets Implementation

[sherintg]

The DAV_v2 allocator now includes support for Spill Over Evictable Buckets (SOEMB). All global allocations will continue to utilize the standard non-evictable memory buckets, while spillover allocations from evictable memory buckets will be directed to SOEMB. In the current implementation, SOEMB remains locked in the memory cache, similar to the behavior of non-evictable memory buckets.

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[github-actions]

Ticket title is 'Spill Over Evictable Buckets (SOEMB) Implementation'
Status is 'Open'
Labels: 'md_on_ssd2'
https://daosio.atlassian.net/browse/DAOS-16896

[NiuYawei]

This might needs be done before the umem_cache_reserve() call in the future?

When we support turning SOE bucket to evict-able (once a SOE bucket isn't qualified as a SOE anymore), allocator might need to pass the SOE set to umem_cache_reserve(), so that we can ensure that all SOE buckets are loaded in umem_cache_reserve().

[NiuYawei]

I don't quite follow the logic here (and the SOE selecting in heap_soemb_active_get()), are we trying to use the buckets in SOE set in a round-robin manner?

[NiuYawei]

Above loop is to create ensure there is always 1 available SOE bucket or SOEMB_ACTIVE_CNT buckets? (The loop breaks if any bucket setup successfully).

I think the goal here is to ensure enough free space being pinned in memory for the potential spilling over happened in next transaction, right? So we'd replace any unqualified bucket (in 'svec') with qualified one to satisfy the space requirement. It looks to me it's too late to remove the unqualified bucket from 'svec' in heap_recycle_soembs().