Server-side Cache Module

Overview

This module is now fairly simple, and might well be regarded as part of the SSKM. It sequesters a large amount of system RAM for use by the NMS system, and it maintains a hash table that maps GPIs to the location of the corresponding data page in RAM, as well as a cached copy of the corresponding metadata. The primary function of the SSCM is to make it possible for the CSKM to determine as quickly as possible whether a data page associated with a particular GPI is currently resident in RAM on this server.

The SSCM also provides ioctl() calls that the SSD can invoke to cause the transfer of data pages between main memory and backing store.

The SSCM only caches metadata for pages currently in RAM. This permits, e.g. permissions and sanity checking to occur in the SSKM before issuing a data page in response to a client request. The master copy of the metadata for all pages is held in a database maintained by the SSD. The SSD keeps this metadata up-to-date by processing events generated by the CSKM when data pages arrive.

Interfaces

Ioctl Interface to SSD

The SSD provides the following ioctl() to the SSD:

• Set maximum size of NMS cache.
• Get/set metadata associated with GPI.
• Page out page from RAM to backing store.
• Page in page from backing store to RAM.
• Free cached data and metadata:
  • By GPI.
  • By client ID.
  • By client ID and virtual unit number.

Procedure Interface with SSKM

The SSD provides the following procedural interface to the SSKM:

• Lookup page by GPI and return address of data and metadata if resident.
• Store data and metadata in cache, associated with a specified GPI.
• Get free page of RAM to be used for data reception.

Description