Glauber Costa 1d7617723d row cache: pin real dirty during cache updates. ...

Right now, once a region is moved to the cache is no longer visible to
the dirty memory system. Not as real dirty nor virtual dirty.

The problem is that until a particular partition is moved to the cache
it is not evictable. As a result we can OOM the system if we have a lot
of pending cache updates as the writes will not be throttled and memory
won't be made available.

This patch pins the memory used by the region as real dirty before the
cache update starts, and unpins it when it is over. In the mean time it
gradually releases memory of the partitions that are being moved to
cache.

I have verified in a couple of workloads that the amount of memory
accounted through this is the same amount of memory accounted through
the memtable flush procedure.

Fixes #1942

Signed-off-by: Glauber Costa <glauber@scylladb.com>

2017-11-08 19:46:36 -05:00

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