Invoking input/output (I/O) threads on processors to demote tracks from a cache

• US 10,082,958 B2
• Filed: 03/27/2018
• Issued: 09/25/2018
• Est. Priority Date: 06/06/2016
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Ash, Kevin J., Borlick, Matthew G., Gupta, Lokesh M., Nguyen, Trung N.
• Primary Examiner(s): Gu, Shawn X
• Application Number:
  US15/937,753
• Publication Number:
  US 20180217759A1
• Time in Patent Office: 182 Days
• CPC Class Codes: G06F 12/0804 with main memory updating G06F12/0806 takes precedence
• CPC Class Codes: G06F 12/0817 using directory methods
• CPC Class Codes: G06F 12/084 with a shared cache
• CPC Class Codes: G06F 12/0842 for multiprocessing or multitasking
• CPC Class Codes: G06F 12/0866 for peripheral storage systems, e.g. disk cache
• CPC Class Codes: G06F 12/0891 using clearing, invalidating or resetting means
• CPC Class Codes: G06F 12/123 with age lists, e.g. queue, most recently used [MRU] list or least recently used [LRU] list
• CPC Class Codes: G06F 12/124 being minimized, e.g. non MRU
• CPC Class Codes: G06F 2212/1024 Latency reduction
• CPC Class Codes: G06F 2212/60 Details of cache memory
• CPC Class Codes: G06F 2212/621 Coherency control relating to peripheral accessing, e.g. from DMA or I/O device
• CPC Class Codes: G06F 3/0605 by facilitating the interaction with a user or administrator
• CPC Class Codes: G06F 3/0653 Monitoring storage devices or systems
• CPC Class Codes: G06F 3/0659 Command handling arrangements, e.g. command buffers, queues, command scheduling
• CPC Class Codes: G06F 3/067 Distributed or networked storage systems, e.g. storage area networks [SAN], network attached storage [NAS]

Abstract

Provided are a computer program product, system, and method for invoking Input/Output (I/O) threads on processors to demote tracks from a cache. An Input/Output (I/O) thread, executed by a processor, processes I/O requests directed to tracks in the storage by accessing the tracks in the cache. After processing at least one I/O request, the I/O thread determines whether a number of free cache segments in the cache is below a free cache segment threshold. The I/O thread processes a demote ready list, indicating tracks eligible to demote from the cache, to demote tracks from the cache in response to determining that the number of free cache segments is below the free cache segment threshold. The I/O thread continues to process I/O requests directed to tracks from the storage stored in the cache after processing the demote ready list to demote tracks in the cache.

Claims

1. A computer program product for managing tracks in a storage in a cache, the computer program product comprising a computer readable storage medium having computer readable program code embodied therein that when executed performs operations, the operations comprising:

invoking a plurality of demote threads on a plurality of processors to demote tracks in the cache;

in response to being invoked, requesting by each demote thread of the invoked demote threads, whether a lock is held to a demote ready list indicating tracks eligible to demote from the cache, wherein the lock serializes access to the demote ready list by the invoked demote threads;

obtaining the lock, by a demote thread requesting the lock, in response to the lock being available;

processing, by the demote thread obtaining the lock, the demote ready list to demote tracks from the cache; and

releasing the lock in response to demoting the tracks eligible to demote from the cache.

2. The computer program product of claim 1, wherein the plurality of demote threads are invoked in response to determining that a number of free cache segments is below a free cache segment threshold, wherein the operations further comprise:

incrementing, by the demote thread obtaining the lock, the number of free cache segments freed by the tracks demoted from the cache.

3. The computer program product of claim 1, wherein the invoking the plurality of demote threads comprises:

determining, by a demote scheduler task, a lowest free cache segment threshold of a plurality of free cache segment thresholds that a number of free cache segments in the cache is below, wherein a number of the demote threads invoked by the demote scheduler task is based on the lowest free cache segment threshold.

4. The computer program product of claim 3, wherein only one demote thread is invoked in response to the determined lowest free cache segment threshold being a highest of the free cache segment thresholds.

5. The computer program product of claim 1, wherein the operations further comprise:

determining, by an Input/Output (I/O) thread processing I/O requests to the cache, whether a number of free cache segments is below a free cache segment threshold;

requesting, by the I/O thread, the lock for the demote ready list in response to determining that the number of free cache segments is below a free cache segment threshold;

processing, by the I/O thread, the demote ready list to demote tracks from the cache in response to obtaining the lock; and

releasing the lock in response to demoting the tracks from the cache.

6. The computer program product of claim 5, wherein the operations further comprise:

determining, by the I/O thread, whether to wait for the lock in response to determining that the lock is not available;

waiting for the lock to become available to obtain the lock to process the demote ready list to demote tracks from the cache in response to determining to wait for the lock to become available; and

returning to processing, by the I/O thread, to process I/O requests in response to determining not to wait for the lock.

7. The computer program product of claim 6, wherein the determining by the I/O thread whether to wait for the lock comprises:

determining to wait for the lock in response to determining that a number of free cache segments is below a free cache segment threshold; and

determining to not wait for the lock in response to determining that the number of free cache segments is less than the free cache segment threshold.

8. A system for managing tracks in a storage, comprising:

a plurality of processors;

a cache; and

computer readable storage medium having computer readable program code embodied therein that when executed performs operations, the operations comprising;

invoking a plurality of demote threads on a plurality of processors to demote tracks in the cache;

in response to being invoked, requesting by each demote thread of the invoked demote threads, whether a lock is held to a demote ready list indicating tracks eligible to demote from the cache, wherein the lock serializes access to the demote ready list by the invoked demote threads;

obtaining the lock, by a demote thread requesting the lock, in response to the lock being available;

processing, by the demote thread obtaining the lock, the demote ready list to demote tracks from the cache; and

releasing the lock in response to demoting the tracks eligible to demote from the cache.

9. The system of claim 8, wherein the plurality of demote threads are invoked in response to determining that a number of free cache segments is below a free cache segment threshold, wherein the operations further comprise:

incrementing, by the demote thread obtaining the lock, the number of free cache segments freed by the tracks demoted from the cache.

10. The system of claim 8, wherein the invoking the plurality of demote threads comprises:

determining, by a demote scheduler task, a lowest free cache segment threshold of a plurality of free cache segment thresholds that a number of free cache segments in the cache is below, wherein a number of the demote threads invoked by the demote scheduler task is based on the lowest free cache segment threshold.

11. The system of claim 10, wherein only one demote thread is invoked in response to the determined lowest free cache segment threshold being a highest of the free cache segment thresholds.

12. The system of claim 8, wherein the operations further comprise:

determining, by an Input/Output (I/O) thread processing I/O requests to the cache, whether a number of free cache segments is below a free cache segment threshold;

requesting, by the I/O thread, the lock for the demote ready list in response to determining that the number of free cache segments is below a free cache segment threshold;

processing, by the I/O thread, the demote ready list to demote tracks from the cache in response to obtaining the lock; and

releasing the lock in response to demoting the tracks from the cache.

13. The system of claim 12, wherein the operations further comprise:

determining, by the I/O thread, whether to wait for the lock in response to determining that the lock is not available;

waiting for the lock to become available to obtain the lock to process the demote ready list to demote tracks from the cache in response to determining to wait for the lock to become available; and

returning to processing, by the I/O thread, to process I/O requests in response to determining not to wait for the lock.

14. The system of claim 13, wherein the determining by the I/O thread whether to wait for the lock comprises:

determining to wait for the lock in response to determining that a number of free cache segments is below a free cache segment threshold; and

determining to not wait for the lock in response to determining that the number of free cache segments is less than the free cache segment threshold.

15. A method for managing tracks in a storage in a cache, comprising:

invoking a plurality of demote threads on a plurality of processors to demote tracks in the cache;

in response to being invoked, requesting by each demote thread of the invoked demote threads, whether a lock is held to a demote ready list indicating tracks eligible to demote from the cache, wherein the lock serializes access to the demote ready list by the invoked demote threads;

obtaining the lock, by a demote thread requesting the lock, in response to the lock being available;

processing, by the demote thread obtaining the lock, the demote ready list to demote tracks from the cache; and

releasing the lock in response to demoting the tracks eligible to demote from the cache.

16. The method of claim 15, wherein the plurality of demote threads are invoked in response to determining that a number of free cache segments is below a free cache segment threshold, further comprising:

incrementing, by the demote thread obtaining the lock, the number of free cache segments freed by the tracks demoted from the cache.

17. The method of claim 15, wherein the invoking the plurality of demote threads comprises:

determining, by a demote scheduler task, a lowest free cache segment threshold of a plurality of free cache segment thresholds that a number of free cache segments in the cache is below, wherein a number of the demote threads invoked by the demote scheduler task is based on the lowest free cache segment threshold.

18. The method of claim 17, wherein only one demote thread is invoked in response to the determined lowest free cache segment threshold being a highest of the free cache segment thresholds.

19. The method of claim 15, further comprising:

determining, by an Input/Output (I/O) thread processing I/O requests to the cache, whether a number of free cache segments is below a free cache segment threshold;

requesting, by the I/O thread, the lock for the demote ready list in response to determining that the number of free cache segments is below a free cache segment threshold;

processing, by the I/O thread, the demote ready list to demote tracks from the cache in response to obtaining the lock; and

releasing the lock in response to demoting the tracks from the cache.

20. The method of claim 19, further comprising:

determining, by the I/O thread, whether to wait for the lock in response to determining that the lock is not available;

waiting for the lock to become available to obtain the lock to process the demote ready list to demote tracks from the cache in response to determining to wait for the lock to become available; and

returning to processing, by the I/O thread, to process I/O requests in response to determining not to wait for the lock.