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From:   Daire Byrne <daire@dneg.com>
Date:   Thu, 1 Sep 2022 16:27:43 +0100
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Subject: Re: directory caching & negative file lookups?
To:     Trond Myklebust <trondmy@hammerspace.com>
Cc:     "linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>
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On Thu, 1 Sept 2022 at 14:55, Trond Myklebust <trondmy@hammerspace.com> wrote:
> man 5 nfs
>
> Look for the section on the 'lookupcache=mode' mount option.

So I get that the client caches negative lookups once we've made them
(the default lookupcache=all), but what I'm wondering is if we have
already cached the entire directory contents before the (negative)
lookup, can we not reply that it doesn't exist using that information
without having to go across the wire the at all (even the first time)?

Or is there no concept of "cached directory contents"? I thought that
maybe readdir/readdirplus knew about the "full contents" of a
directory?

My thinking was that if we did a readdir/readirplus first, we could
then do lookups for any random non-existent filename without having to
send anything across the wire. Like I said, a newbie question with
limited understanding of the actual internals :)

Daire