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Date: Wed, 8 May 2024 09:43:40 -0400
From: Chuck Lever <chuck.lever@oracle.com>
To: Amir Goldstein <amir73il@gmail.com>
Cc: linux-nfs@vger.kernel.org
Subject: Re: long-term stable backports of NFSD patches
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On Wed, May 08, 2024 at 02:29:05PM +0300, Amir Goldstein wrote:
> On Mon, May 6, 2024 at 4:25 PM Chuck Lever <chuck.lever@oracle.com> wrote:
> >
> > It's apparent that a number of distributions and their customers
> > remain on long-term stable kernels. We are aware of the scalability
> > problems and other bugs in NFSD in kernels between v5.4 and v6.1.
> >
> 
> Chuck,
> 
> Are you able to share a partial list of scalability problems that were
> fixed by this backport series?
> 
> Specifically, my interest is in the list of improvements to 5.15.y.

In broad strokes:

- The garbage collection mechanism was rewritten to keep the LRU
  list short, and to keep sweeps productive. This was the main issue
  as the LRU used to have hundreds of thousands of files on it and
  one sweep would take so much CPU it was reported as a soft lockup.
- NFSv4 OPEN files are no longer garbage collected so that an NFSv4
  CLOSE means local accessors have immediate access to a file.
- The filecache hash table is converted to an rhltable so that it
  can efficiently manage many more open files.
- Various fixes prevent writeback of garbage-collected files from
  bogging down.

There are a handful of important bugfixes before this commit, but
starting with commit 0369b53886ec ("NFSD: Report filecache LRU
size"), have a look at the commits that touch fs/nfsd/filecache.c.

-- 
Chuck Lever