linux-kernel - Re: 5.4.188 and later: massive performance regression with nfsd

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Message-ID: <6A15DEE1-CAC9-4C64-8643-AD28EA423046@oracle.com>
Date:   Wed, 11 May 2022 14:16:19 +0000
From:   Chuck Lever III <chuck.lever@...cle.com>
To:     Greg KH <gregkh@...uxfoundation.org>,
        Wolfgang Walter <linux@...m.de>
CC:     linux-stable <stable@...r.kernel.org>,
        Trond Myklebust <trondmy@...il.com>,
        Linux NFS Mailing List <linux-nfs@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: 5.4.188 and later: massive performance regression with nfsd



> On May 11, 2022, at 8:38 AM, Greg KH <gregkh@...uxfoundation.org> wrote:
> 
> On Wed, May 11, 2022 at 12:03:13PM +0200, Wolfgang Walter wrote:
>> Hi,
>> 
>> starting with 5.4.188 wie see a massive performance regression on our
>> nfs-server. It basically is serving requests very very slowly with cpu
>> utilization of 100% (with 5.4.187 and earlier it is 10%) so that it is
>> unusable as a fileserver.
>> 
>> The culprit are commits (or one of it):
>> 
>> c32f1041382a88b17da5736886da4a492353a1bb "nfsd: cleanup
>> nfsd_file_lru_dispose()"
>> 628adfa21815f74c04724abc85847f24b5dd1645 "nfsd: Containerise filecache
>> laundrette"
>> 
>> (upstream 36ebbdb96b694dd9c6b25ad98f2bbd263d022b63 and
>> 9542e6a643fc69d528dfb3303f145719c61d3050)
>> 
>> If I revert them in v5.4.192 the kernel works as before and performance is
>> ok again.
>> 
>> I did not try to revert them one by one as any disruption of our nfs-server
>> is a severe problem for us and I'm not sure if they are related.
>> 
>> 5.10 and 5.15 both always performed very badly on our nfs-server in a
>> similar way so we were stuck with 5.4.
>> 
>> I now think this is because of 36ebbdb96b694dd9c6b25ad98f2bbd263d022b63
>> and/or 9542e6a643fc69d528dfb3303f145719c61d3050 though I didn't tried to
>> revert them in 5.15 yet.
> 
> Odds are 5.18-rc6 is also a problem?

We believe that

6b8a94332ee4 ("nfsd: Fix a write performance regression")

addresses the performance regression. It was merged into 5.18-rc.


> If so, I'll just wait for the fix to get into Linus's tree as this does
> not seem to be a stable-tree-only issue.

Unfortunately I've received a recent report that the fix introduces
a "sleep while spinlock is held" for NFSv4.0 in rare cases.


--
Chuck Lever