Two-phase eviction process for file handle caches

• US 10,684,989 B2
• Filed: 06/15/2011
• Issued: 06/16/2020
• Est. Priority Date: 06/15/2011
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Inventors: Vasquez Lopez, Daniel, Yoo, Won
• Primary Examiner(s): Thomas, Ashish
• Assistant Examiner(s): Mahmood, Rezwanul
• Application Number:
  US13/160,963
• Publication Number:
  US 20120323872A1
• Time in Patent Office: 3,289 Days
• CPC Class Codes: G06F 16/172 Caching, prefetching or hoarding of files

Abstract

Systems and methods are provided for evicting entries from a file handle cache. In accordance with certain embodiments, a two-stage eviction process is utilized. In a first stage of the eviction process, entries in the file entry cache are analyzed and marked for eviction while a shared lock is maintained on the file handle cache. The shared lock enables the file handle cache to be concurrently accessed by a content serving system to service content requests. In a second stage of the eviction process, entries in the file handle cache that are marked for eviction are removed while an exclusive lock is maintained on the file handle cache. The exclusive lock prevents the content serving system from concurrently accessing the file handle cache to service content requests.

Claims

1. A method for evicting entries from a file handle cache, each entry in the file handle cache storing a file handle associated with an open file in a file system, the method comprising:

analyzing each entry in the file handle cache to identify entries to be marked for eviction and marking the identified entries for eviction while maintaining a shared lock on the entire file handle cache, the shared lock allowing the file handle cache to be concurrently accessed by one or more processes to obtain file handles for use in servicing requests for content from the file system; and

removing the entries marked for eviction from the file handle cache while maintaining an exclusive lock on the entire file handle cache, the exclusive lock preventing the file handle cache from being concurrently accessed by the one or more processes.

2. The method of claim 1, wherein removing the entries marked for eviction from the file handle cache comprises moving the entries marked for eviction to a deletion list, the method further comprising:

issuing commands to the file system to close each open file associated with a file handle stored in the deletion list while not maintaining any lock on the file handle cache.

3. The method of claim 2, further comprising deleting content from one or more of system memory and a disk that is associated with each file that is closed by the file system.

4. The method of claim 1, wherein analyzing each entry in the file handle cache to identify entries to be marked for eviction comprises:

determining if a time to live value associated with each entry has expired; and

identifying an entry as an entry to be marked for eviction if the time to live value associated therewith has expired.

5. The method of claim 4, wherein determining if the time to live value associated with each entry has expired comprises:

decrementing the time to live value associated with a particular entry in the file handle cache; and

determining if the decremented time to live value is zero.

6. The method of claim 4, wherein analyzing each entry in the file handle cache to identify entries to be marked for eviction further comprises:

modifying the time to live value associated with each entry if a measure of system memory utilization exceeds a threshold.

7. The method of claim 1, wherein analyzing each entry in the file handle cache to identify entries to be marked for eviction comprises:

comparing a hit count associated with each entry in the file handle cache to a statistical threshold, the hit count associated with each entry representing a number of times that the entry was accessed to service a request for content from the file system; and

identifying a particular entry in the file handle cache as an entry to be marked for eviction if the hit count associated therewith is less than the statistical threshold.

8. The method of claim 7, further comprising:

calculating the statistical threshold based on the hit counts associated with all of the entries in the file handle cache.

9. The method of claim 8, wherein calculating the statistical threshold based on the hit counts associated with all of the entries in the file handle cache comprises calculating a standard deviation based on the hit counts associated with all of the entries in the file handle cache.

10. The method of claim 7, further comprising:

resetting a particular hit count associated with a particular entry in the file handle cache if a predetermined amount of time has elapsed since a last time that the particular hit count associated with the particular entry was reset, wherein each entry of the file handle cache is associated with a respective hit count.

11. The method of claim 10, further comprising:

calculating a mean value based on the hit counts associated with all of the entries in the file handle cache;

wherein resetting the particular hit count associated with the particular entry comprises resetting the particular hit count associated with the particular entry to the mean value.

12. A system, comprising:

at least one processor;

memory connected to the at least one processor;

a file system stored at least in part in the memory and executed by the at least one processor; and

a content serving system stored at least in part in the memory and executed by the at least one processor, the content serving system being configured to service requests for content by accessing files on the file system, the content serving system including;

a file handle cache having a plurality of entries, each entry in the file handle cache storing a file handle associated with an open file in the file system, the file handle cache being accessible to obtain file handles for accessing open files on the file system; and

file handle cache management logic that is configured to analyze a time to live counter assigned to each entry in the file handle cache and to mark an entry for eviction if the time to live counter assigned thereto has expired, the value of the time to live counter that is assigned to each entry in the file handle cache being adaptively determined based on a measure of utilization of a system memory that stores contents of each open file associated with each file handle stored in the file handle cache, the system memory being a different entity than the file handle cache.

13. The system of claim 12, wherein the file handle cache management logic is configured to analyze the time to live counter assigned to each entry in the file handle cache and to mark an entry for eviction if the time to live counter assigned thereto has expired while maintaining a shared lock on the file handle cache.

14. The system of claim 13, wherein the file handle cache management logic is further configured to remove each entry marked for eviction from the file handle cache while maintaining an exclusive lock on the file handle cache.

15. The system of claim 12, wherein the value of the time to live counter that is assigned to each entry in the file handle cache is adaptively assigned based on whether the measure of system memory utilization exceeds a first threshold and a second threshold.

16. A system, comprising:

at least one processor;

a memory connected to the at least on processor;

a file system stored at least in part in the memory and executed by the at least one processor;

a file handle cache stored at least in part in the memory, each entry in the file handle cache storing a file handle associated with an open file in the file system; and

file handle cache management logic configured to;

analyze each entry in the file handle cache to identify entries to be marked for eviction and mark the identified entries for eviction while maintaining a shared lock on the entire file handle cache, the shared lock allowing the file handle cache to be concurrently accessed by one or more processes to obtain file handles for use in servicing requests for content from the file system; and

remove the entries marked for eviction from the file handle cache while maintaining an exclusive lock on the entire file handle cache, the exclusive lock preventing the file handle cache from being concurrently accessed by the one or more processes.

17. The system of claim 16, wherein the file handle cache management logic is configured to remove the entries marked for eviction from the file handle cache by moving the entries marked for eviction to a deletion list, the file handle cache management logic further configured to:

issue commands to the file system to close each open file associated with a file handle stored in the deletion list while not maintaining any lock on the file handle cache.

18. The system of claim 17, wherein the file handle cache management logic is configured to delete content from one or more of system memory and a disk that is associated with each file that is closed by the file system.

19. The system of claim 16, wherein the file handle cache management logic is configured to analyze each entry in the file handle cache to identify entries to be marked for eviction by:

determining if a time to live value associated with each entry has expired; and

identifying an entry as an entry to be marked for eviction if the time to live value associated therewith has expired.

20. The system of claim 19, wherein the file handle cache management logic is configured to determine if the time to live value associated with each entry has expired by:

decrementing the time to live value associated with a particular entry in the file handle cache; and

determining if the decremented time to live value is zero.