correct handling for expired items in eviction

[byrnedj]

We first check if an item is expired under mmContainer lock and if so mark it for eviction so it is recycled back up to allocateInternalTier.

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This change is 

[igchor]

Reviewable status: 0 of 1 files reviewed, 1 unresolved discussion (waiting on @byrnedj)

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cachelib/allocator/CacheAllocator-inl.h line 1811 at r1 (raw file):

    TierId tid, PoolId pid, Item& item, bool fromBgThread) {
  XDCHECK(item.isMoving());
  XDCHECK(!item.isExpired());

I think the item can still become expired after we exit the MMContainer critical section - we should remove this assert. From a correctness perspective I think that's fine (it can become expired anytime I think), we can just evict the item and find() will handle it properly.

[byrnedj]

Reviewable status: 0 of 1 files reviewed, 1 unresolved discussion (waiting on @igchor)

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cachelib/allocator/CacheAllocator-inl.h line 1811 at r1 (raw file):

Previously, igchor (Igor Chorążewicz) wrote…

I think the item can still become expired after we exit the MMContainer critical section - we should remove this assert. From a correctness perspective I think that's fine (it can become expired anytime I think), we can just evict the item and find() will handle it properly.

Done.