Fast cache demotions in storage controllers with metadata

Abstract

Provided are techniques for fast cache demotions in storage controllers with metadata. A track in a demotion structure is selected. In response to determining that the track in the demotion structure does not have invalidate metadata set, demoting the track from cache. In response to determining that the track has invalidate metadata set, the track is moved from the demotion structure to an invalidate metadata structure. One or more tasks are created to process the invalidate metadata structure, wherein each of the one or more tasks selects a different track in the invalidate metadata structure, invalidates metadata for that track, and demotes that track.

Description

BACKGROUND1. Field of the Invention[0001]Embodiments of the invention relate to fast cache demotions in storage controllers with metadata.2. Description of the Related Art[0002]A storage controller is coupled to cache and to storage, which is divided into volumes. The storage may be a Redundant Array of Independent Disks (RAID) array.[0003]A track in cache may be marked to say “invalidate metadata”. The cache cannot demote the tracks marked with “invalidate metadata” without first invalidating that metadata. Cache demotion refers to removing unmodified data from cache to make room in cache. If cache demotion comes across these tracks with “invalidate metadata”, then, typically, the cache demotion either 1) skips these tracks or 2) moves them to a Most Recently Used (MRU) end of a list of tracks to avoid encountering them again during the cache demotion.[0004]Count Key Data (CKD) may be described as a data recording format. For CKD volumes in storage, the cache maintains metadata for...

AI Technical Summary

Benefits of technology

This approach enables faster and more efficient cache demotions by isolating metadata invalidation tasks, preventing deadlocks and ensuring continuous processing without performance bottlenecks.

Problems solved by technology

CKD tracks with invalidate metadata set cannot be demoted from cache without first accessing the metadata and marking it invalid.

Invalidating the metadata is an expensive operation since the metadata for the track needs to be accessed, which may cause a stage of the metadata from the CKD volume to cache.

However, there are problems with these approaches.

If the tracks are moved to the MRU end of the list of tracks, then the cache demotion will encounter the tracks when it is processing the MRU end and many of the tracks at the MRU end may be the tracks with “invalidate metadata”, which creates a deadlock.

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