Re: [PATCH 0/4] nfsd: filecache: change garbage collect lists

NeilBrown
2025-01-22T22:16:21Z

On Thu, 23 Jan 2025, Chuck Lever wrote:
> On 1/21/25 10:54 PM, NeilBrown wrote:
> >
> > The nfsd filecache currently uses list_lru for tracking files recently
> > used in NFSv3 requests which need to be "garbage collected" when they
> > have becoming idle - unused for 2-4 seconds.
> >
> > I do not believe list_lru is a good tool for this. It does no allow the
> > timeout which filecache requires so we have to add a timeout mechanism
> > which holds the list_lru for while the whole list is scanned looking for
> > entries that haven't been recently accessed. When the list is largish
> > (even a few hundred) this can block new requests which need the lock to
> > remove a file to access it.
> >
> > This patch removes the list_lru and instead uses 2 simple linked lists.
> > When a file is accessed it is removed from whichever list it is one,
> > then added to the tail of the first list. Every 2 seconds the second
> > list is moved to the "freeme" list and the first list is moved to the
> > second list. This avoids any need to walk a list to find old entries.
> >
> > These lists are per-netns rather than global as the freeme list is
> > per-netns as the actual freeing is done in nfsd threads which are
> > per-netns.
> >
> > This should not be applied until we resolve how to handle the
> > race-detection code in nfsd_file_put(). However I'm posting it now to
> > get any feedback so that a final version can be posted as soon as that
> > issue is resolved.
> >
> > Thanks,
> > NeilBrown
> >
> >
> > [PATCH 1/4] nfsd: filecache: use nfsd_file_dispose_list() in
> > [PATCH 2/4] nfsd: filecache: move globals nfsd_file_lru and
> > [PATCH 3/4] nfsd: filecache: change garbage collection list
> > [PATCH 4/4] nfsd: filecache: change garbage collection to a timer.
>
> Hi Neil -
>
> I would like Dave Chinner to chime in on this approach. When you
> resend, please Cc: him. Thanks!

Sure, I can do that. But why Dave in particular?
I would like to add a comment to the cover letter explaining to Dave
what he was added to see and I don't know what to say.

Thanks,
NeilBrown