Add shrinklat and xfs_reclaim examples #40
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This is quite eye opening in terms of how bad page allocation slow path can be:
Multiple XFS filesystem in turn show this picture:
The culprit appears to be the desire to flush as many inodes from cache as possible, not matter if they are dirty or clean. This doesn't play very well when a system has 100GB of page cache and 1GB of dirty pages that can be flushed on disk. Kernel opts into flushing pages on (potentially very slow) storage, while page cache can be reclaimed at near zero cost.