Distributed management of file modification-time field

1. A method for data storage, comprising:

using File System (FS) software executing on data processing hardware, storing a file in non-volatile storage in communication with the data processing hardware, wherein the file comprises a latest-time value that is exposed to external applications and is indicative of a most-recent time that a storage operation was performed in the file;

executing, by the FS software, a software owner module, the software owner module designated as an owner of the file and configured to manage the latest-time value of the file;

executing, by the FS software, a plurality of software mapper modules on the data processing hardware, each software mapper module executing on the data processing hardware configured to:

access a respective portion of the file stored in the non-volatile storage, the respective portion of the file assigned to the corresponding software mapper module by the software owner module, and the respective portion of the file different than the respective portions of the file assigned to each of the other software mapper modules of the plurality of software mapper modules; and

manage and update a respective local value indicative of a most-recent time at which the respective portion of the file was subject to a storage operation by the corresponding software mapper module; and

permitting, by the FS software, the plurality of software mapper modules to operate on the file simultaneously, while continually maintaining the latest-time value exposed to the external applications by:

each time one of the plurality of software mapper modules performs the storage operation on the respective portion of the file assigned to the corresponding software mapper module by the software owner module, the corresponding software mapper module:

updates the respective local value of the respective portion of the file managed by the corresponding software mapper module,

stores the updated respective local value of the respective portion of the file in the non-volatile storage, and

passes a request to update the latest-time value to the software owner module designated as the owner of the file, the request including the updated respective local value; and

updating, by the software owner module designated as the owner of the file, the latest-time value that is exposed to the external applications for the file, by consolidating the latest-time value with update requests received from the software mapper modules, wherein consolidating the latest-time value with the update requests comprises:

comparing the updated local value of the received update requests to the latest-time value;

when the updated local value is greater than the latest-time value, replacing the latest-time value with the updated local value; and

when the updated local value is not greater than the latest-time value, incrementing the latest-time value by a predefined increment, and

wherein the software owner module executing by the FS software on the data processing hardware prevents more than one of the plurality of software mapper modules from performing the storage operation on a same portion of the file simultaneously.

2. The method according to claim 1 , wherein the storage operations comprise write operations that modify content of the file, and wherein the local values and the latest-time value comprise modification-time (mTime) values that are indicative of most-recent times the content of the file was modified.

3. The method according to claim 2 , wherein updating the local modification-time values comprises temporarily storing the updated local modification-time values together with a corresponding modified content in the non-volatile storage.

4. The method according to claim 3 , further comprising generating and storing a snapshot of the file that comprises the modified content, and deleting the temporarily-stored updated local modification-time values from the non-volatile storage.

5. The method according to claim 2 , further comprising, upon recovery from a failure, determining a count of currently-open write operations to the file, and setting the latest-time value that is exposed to the external applications to an updated value depending on the count.

6. The method according to claim 1 , wherein the predefined increment comprises a finest-resolution increment in a format of the latest-time value.

7. The method according to claim 1 , further comprising, upon recovery from a failure, setting the global modification-time to an updated value depending on the predefined increment.

8. The method according to claim 1 , wherein the storage operations comprise read and write operations, and wherein the local values and the latest-time value comprise access-time (aTime) values that are indicative of most-recent times the file was accessed.

9. A computing system, comprising:

a non-volatile storage; and

one or more processors executing File System (FS) software, which are configured to:

using the FS software, store a file in the non-volatile storage, wherein the file comprises a latest-time value that is exposed to external applications and is indicative of a most-recent time that a storage operation was performed on the file;

execute, by the FS software, a software owner module, the software owner module designated as an owner of the file and configured to manage the latest-time value of the file;

execute, by the FS software, a plurality of software mapper modules on the data processing hardware, each software mapper module executing on the data processing hardware configured to:

access a respective portion of the file stored in the non-volatile storage, the respective portion of the file assigned to the corresponding software mapper module by the software owner module, and the respective portion of the file different than the respective portions of the file assigned to each of the other software mapper modules of the plurality of software mapper modules; and

manage and update a respective local value indicative of a most-recent time at which the respective portion of the file was subject to a storage operation by the corresponding software mapper module; and

permit, by the FS software, the plurality of software mapper modules to operate on the file simultaneously, while continually maintaining the latest-time value exposed to the external applications by:

each time one of the plurality of software mapper modules performs the storage operation on the respective portion of the file assigned to the corresponding software mapper module by the software owner module, the corresponding software mapper module:

updates the respective local value of the respective portion of the file managed by the corresponding software mapper module,

stores the updated respective local value of the respective portion of the file in the non-volatile storage, and

passes a request to update the latest-time value to the software owner module designated as the owner of the file, the request including the updated respective local value; and

updating, by the software owner module designated as the owner of the file, the latest-time value that is exposed to the external applications for the file, by consolidating the latest-time value with update requests received from the software mapper modules, wherein consolidating the latest-time value with the update requests comprises:

comparing the updated local value of the received update requests to the latest-time value;

when the updated local value is greater than the latest-time value, replacing the latest-time value with the updated local value; and

when the updated local value is not greater than the latest-time value, incrementing the latest-time value by a predefined increment, and

wherein the software owner module executing by the FS software on the data processing hardware prevents more than one of the plurality of software mapper modules from performing the storage operation on a same portion of the file simultaneously.

10. The system according to claim 9 , wherein the storage operations comprise write operations that modify content of the file, and wherein the local values and the latest-time value comprise modification-time (mTime) values that are indicative of most-recent times the content of the file was modified.

11. The system according to claim 10 , wherein the one or more processors are configured to temporarily store the updated local modification-time values together with a corresponding modified content in the non-volatile storage.

12. The system according to claim 11 , wherein the one or more processors are configured to generate and store a snapshot of the file that comprises the modified content, and to delete the temporarily-stored updated local modification-time values from the non-volatile storage.

13. The system according to claim 10 , wherein, upon recovery from a failure, the one or more processors are configured to determine a count of currently-open write operations to the file, and to set the global modification-time to an updated value depending on the count.

14. The system according to claim 9 , wherein the predefined increment comprises a finest-resolution increment in a format of the latest-time value.

15. The system according to claim 9 , wherein, upon recovery from a failure, the one or more processors are configured to set the global modification-time to an updated value depending on the predefined increment.

16. The system according to claim 9 , wherein the storage operations comprise read and write operations, and wherein the local values and the latest-time value comprise access-time (aTime) values that are indicative of most-recent times the file was accessed.