Re: [PATCH] NFSv4.2: fix setattr caching of TIME_[MODIFY|ACCESS]_SET when timestamps are delegated

[Sagi Grimberg <sagi@grimberg.me>]

On 05/05/2025 16:25, Chuck Lever wrote:
> On 4/25/25 8:49 AM, Sagi Grimberg wrote:
>> nfs_setattr will flush all pending writes before updating a file time
>> attributes. However when the client holds delegated timestamps, it can
>> update its timestamps locally as it is the authority for the file
>> times attributes. The client will later set the file attributes by
>> adding a setattr to the delegreturn compound updating the server time
>> attributes.
>>
>> Fix nfs_setattr to avoid flushing pending writes when the file time
>> attributes are delegated and the mtime/atime are set to a fixed
>> timestamp (ATTR_[MODIFY|ACCESS]_SET. Also, when sending the setattr
>> procedure over the wire, we need to clear the correct attribute bits
>> from the bitmask.
>>
>> I was able to measure a noticable speedup when measuring untar performance.
>> Test: $ time tar xzf ~/dir.tgz
>> Baseline: 1m13.072s
>> Patched: 0m49.038s
>>
>> Which is more than 30% latency improvement.
> That's significant. Next step is to ensure this doesn't cause any
> functional regressions. Have you run fstests ?

I have not. But I will. Please note the comment under the '---' separator.
This only make a difference if nfsd grants the client a space_limit with
the write deleg. Without it, untar is still very much synchronous.

>> Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
>> ---
>> Tested this on a vm in my laptop against chuck nfsd-testing which
>> grants write delegs for write-only opens, plus another small modparam
>> that also adds a space_limit to the delegation.