[LU-11962] File LSOM updates to store proper size via FLR for regular stat() usage

Duplicate — Wed, 23 Feb 2022 22:33:59 +0000

The layout manipulations required to bring an FLR file in to sync (READONLY in FLR parlance) also give SOM while the file is in sync. This is true SOM, with no caveats, able to be used for any purpose (as distinct from lazy SOM which can only be used by tools which are aware of it).

In essence, there is no reason the SOM portion has to be associated with a replica. Exactly the same functionality can be used just for SOM.

Because the layout state transitions for FLR require synchronous writes to the MDS each time, and because a write to the file destroys the SOM state, this is too expensive to try to use all the time. Instead, the proposal is to set it on all files a certain amount of time after they have been modified (e.g. 24h). If there are no writes to a file for a time, and the client is returning identical size+blocks in the LSOM state at close time, we take it through the layout transitions to mark it LCM_FL_RDONLY (does not make it not writeable, just indicates the attributes are not being modified), and then it has SOM.

This would be a fairly low effort way to allow all files except those being actively modified to have true SOM and improve performance for normal stat() and similar calls.

Whamcloud Community JIRA

[LU-11962] File LSOM updates to store proper size via FLR for regular stat() usage