[LU-549] Add xattr list/value cache on client

Related — Thu, 13 Jun 2013 19:00:39 +0000

Caching the xattr list (and xattrs themselves) on the clients is becoming increasingly important, since this has shown up as a performance problem in the past (e.g. doing an RPC to get "security.capability" for every file access).

We can easily/compatibly add a simple xattr list and/or value cache on the client under the MDS_INODELOCK_UPDATE bit, which setxattr always gets in LCK_EX mode. mdt_reint_setxattr() also gets the MDS_INODELOCK_LOOKUP for XATTR_NAME_ACL_ACCESS, but this should be expanded to also include XATTR_SECURITY_PREFIX. This should also allow negative xattr caching so that an RPC is not sent repeatedly for xattrs that do not exist. Whether we want to cache the non-security xattrs under a separate MDS_INODELOCK_XATTR bit lock can be decided/implemented separately.

A second phase would be to read/send/cache common xattrs on the client on first access to avoid extra RPCs. This will become increasingly important with clients, since SELinux and other xattr-heavy tools are becoming increasingly common.

If we begin to cache xattrs on the client, we should remove the special-case handling of security.capability in ll_setxattr_common() which was added as a hack to address a serious performance problem.

Whamcloud Community JIRA

[LU-549] Add xattr list/value cache on client