lru: Do not add failed objects #4428
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Until now we kept failed objects momentarily on the LRU. This is wasteful, because they never get inserted into EXP (which happens via HSH_Unbusy() -> EXP_Insert), and as such will be removed from cache when the last reference goes away. Why is this change correct? - in HSH_Lookup(), we explicitly skip OC_F_FAILED - the only place where OC_F_FAILED can be gained is HSH_Fail() - HSH_Fail() asserts that the object is still busy - LRU_Add() gets called via HSH_DerefBoc() -> ObjBocDone() when the boc's last reference goes away
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I think this is fine, but I think we should also add an assert in LRU_NukeOne() that nothing on the list has the OC_F_FAILED flag set, so document and enforce that new assumption. |
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Until now we kept failed objects momentarily on the LRU. This is wasteful, because they never get inserted into EXP (which happens via HSH_Unbusy() -> EXP_Insert), and as such will be removed from cache when the last reference goes away.
Why is this change correct?