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Date:   Sat, 21 Nov 2020 19:02:16 -0500
From:   bfields <bfields@fieldses.org>
To:     Daire Byrne <daire@dneg.com>
Cc:     Jeff Layton <jlayton@kernel.org>,
        "J. Bruce Fields" <bfields@redhat.com>,
        Trond Myklebust <trondmy@hammerspace.com>,
        linux-cachefs <linux-cachefs@redhat.com>,
        linux-nfs <linux-nfs@vger.kernel.org>
Subject: Re: [PATCH 2/4] nfsd: pre/post attr is using wrong change attribute
Message-ID: <20201122000216.GE3476@fieldses.org>
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On Sat, Nov 21, 2020 at 09:44:29PM +0000, Daire Byrne wrote:
> ----- On 21 Nov, 2020, at 01:03, Jeff Layton jlayton@kernel.org wrote:
> > On Fri, 2020-11-20 at 17:44 -0500, J. Bruce Fields wrote:
> >> On Fri, Nov 20, 2020 at 05:38:31PM -0500, J. Bruce Fields wrote:
> >> > I think the first one's all that's needed to fix the problem Daire
> >> > identified.  I'm a little less sure of the rest.
> 
> I can confirm that patch 1/8 alone does indeed address the reported revalidation issue for us (as did the previous patch). The re-export server's client cache seems to remain intact and can serve the same cached results to multiple clients.

Thanks again for the testing.

> I should also mention that I still see a lot of unexpected repeat
> lookups even with the iversion optimisation patches with certain
> workloads. For example, looking at a network capture on the re-export
> server I might see 100s of getattr calls to the originating server for
> the same filehandle within 30 seconds which I would have expected the
> client cache to serve. But it could also be that the client cache is
> under memory pressure and not holding that data for very long.

That sounds weird.  Is the filehandle for a file or a directory?  Is the
file or directory actually changing at the time, and if so, is it the
client that's changing it?

Remind me what the setup is--a v3 re-export of a v4 mount?

--b.

> But now I do wonder if these NFSv4 directory modifications and
> pre/post change attributes could be one potential contributor? I might
> run some production loads with a v3 re-export of a v3 server to see if
> that changes anything.
> 
> Many thanks again for the patches, I will take the entire set and run
> them through our production re-export workloads to see if anything
> shakes out.
> 
> Daire