From: Trond Myklebust <trondmy@hammerspace.com>
To: "bcodding@redhat.com" <bcodding@redhat.com>
Cc: "linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>
Subject: Re: [PATCH v6 05/13] NFS: Improve algorithm for falling back to uncached readdir
Date: Mon, 21 Feb 2022 23:20:10 +0000 [thread overview]
Message-ID: <79a2c935bd5b9044c216c90ebfac3dc2e8e6b888.camel@hammerspace.com> (raw)
In-Reply-To: <9DBD587E-C4CA-4674-B47D-92396EEEA082@redhat.com>
On Mon, 2022-02-21 at 16:10 -0500, Benjamin Coddington wrote:
> On 21 Feb 2022, at 15:55, Trond Myklebust wrote:
> >
> > We will always need the ability to cut over to uncached readdir.
>
> Yes.
>
> > If the cookie is no longer returned by the server because one or
> > more
> > files were deleted then we need to resolve the situation somehow
> > (IOW:
> > the 'rm *' case). The new algorithm _does_ improve performance on
> > those
> > situations, because it no longer requires us to read the entire
> > directory before switching over: we try 5 times, then fail over.
>
> Yes, using per-page validation doesn't remove the need for uncached
> readdir.
> It does allow a reader to simply resume filling the cache where it
> left
> off. There's no need to try 5 times and fail over. And there's no
> need to
> make a trade-off and make the situation worse in certain scenarios.
>
> I thought I'd point that out and make an offer to re-submit it. Any
> interest?
>
As I recall, I had concerns about that approach. Can you explain again
how it will work?
A few of the concerns I have revolve around telldir()/seekdir(). If the
platform is 32-bit, then we cannot use cookies as the telldir() output,
and so our only option is to use offsets into the page cache (this is
why this patch carves out an exception if desc->dir_cookie == 0). How
would that work with you scheme?
Even in the 64-bit case where are able to use cookies for
telldir()/seekdir(), how do we determine an appropriate page index
after a seekdir()?
--
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com
next prev parent reply other threads:[~2022-02-21 23:22 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-21 16:08 [PATCH v6 00/13] Readdir improvements trondmy
2022-02-21 16:08 ` [PATCH v6 01/13] NFS: constify nfs_server_capable() and nfs_have_writebacks() trondmy
2022-02-21 16:08 ` [PATCH v6 02/13] NFS: Trace lookup revalidation failure trondmy
2022-02-21 16:08 ` [PATCH v6 03/13] NFS: Adjust the amount of readahead performed by NFS readdir trondmy
2022-02-21 16:08 ` [PATCH v6 04/13] NFS: Simplify nfs_readdir_xdr_to_array() trondmy
2022-02-21 16:08 ` [PATCH v6 05/13] NFS: Improve algorithm for falling back to uncached readdir trondmy
2022-02-21 16:08 ` [PATCH v6 06/13] NFS: Improve heuristic for readdirplus trondmy
2022-02-21 16:08 ` [PATCH v6 07/13] NFS: Don't ask for readdirplus unless it can help nfs_getattr() trondmy
2022-02-21 16:08 ` [PATCH v6 08/13] NFSv4: Ask for a full XDR buffer of readdir goodness trondmy
2022-02-21 16:08 ` [PATCH v6 09/13] NFS: Readdirplus can't help lookup for case insensitive filesystems trondmy
2022-02-21 16:08 ` [PATCH v6 10/13] NFS: Don't request readdirplus when revaldation was forced trondmy
2022-02-21 16:08 ` [PATCH v6 11/13] NFS: Add basic readdir tracing trondmy
2022-02-21 16:08 ` [PATCH v6 12/13] NFS: Trace effects of readdirplus on the dcache trondmy
2022-02-21 16:08 ` [PATCH v6 13/13] NFS: Trace effects of the readdirplus heuristic trondmy
2022-02-23 13:40 ` [PATCH v3 1/8] NFS: save the directory's change attribute on pagecache pages Benjamin Coddington
2022-02-23 13:40 ` [PATCH v3 2/8] NFSv4: Send GETATTR with READDIR Benjamin Coddington
2022-02-23 13:40 ` [PATCH v3 3/8] NFS: Add a struct to track readdir pagecache location Benjamin Coddington
2022-02-23 13:40 ` [PATCH v3 4/8] NFS: Keep the readdir pagecache cursor updated Benjamin Coddington
2022-02-23 13:40 ` [PATCH v3 5/8] NFS: readdir per-page cache validation Benjamin Coddington
2022-02-23 13:40 ` [PATCH v3 6/8] NFS: stash the readdir pagecache cursor on the open directory context Benjamin Coddington
2022-02-23 13:40 ` [PATCH v3 7/8] NFS: Support headless readdir pagecache pages Benjamin Coddington
2022-02-23 13:40 ` [PATCH v3 8/8] NFS: Revalidate the directory pagecache on every nfs_readdir() Benjamin Coddington
2022-02-21 16:45 ` [PATCH v6 05/13] NFS: Improve algorithm for falling back to uncached readdir Benjamin Coddington
2022-02-21 19:58 ` Trond Myklebust
2022-02-21 20:22 ` Benjamin Coddington
2022-02-21 20:55 ` Trond Myklebust
2022-02-21 21:10 ` Benjamin Coddington
2022-02-21 23:20 ` Trond Myklebust [this message]
2022-02-22 12:50 ` Benjamin Coddington
2022-02-22 20:11 ` Trond Myklebust
2022-02-22 20:21 ` Benjamin Coddington
2022-02-23 12:17 ` Trond Myklebust
2022-02-23 13:34 ` Benjamin Coddington
2022-02-23 21:31 ` Trond Myklebust
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