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Date:   Tue, 31 May 2022 22:44:21 +0800
From:   Wang Yugui <wangyugui@e16-tech.com>
To:     Chuck Lever III <chuck.lever@oracle.com>
Subject: Re: [PATCH v2] nfsd: serialize filecache garbage collector
Cc:     Linux NFS Mailing List <linux-nfs@vger.kernel.org>
In-Reply-To: <A12757CE-17B8-4F21-9EC9-3CA0496A8B99@oracle.com>
References: <20220531103427.47769-1-wangyugui@e16-tech.com> <A12757CE-17B8-4F21-9EC9-3CA0496A8B99@oracle.com>
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Hi,

> > On May 31, 2022, at 6:34 AM, Wang Yugui <wangyugui@e16-tech.com> wrote:
> > 
> > When many(>NFSD_FILE_LRU_THRESHOLD) files are kept as OPEN, such as
> > xfstests generic/531, nfsd proceses are in CPU high-load state,
> > and nfsd_file_gc(nfsd filecache garbage collector) waste many CPU times.
> 
> Over the past few days, I've been able to reproduce a lot of bad
> behavior with generic/531. My test client has 12 physical CPU
> cores, and my lab network is 56Gb InfiniBand.
> 
> Unfortunately this patch doesn't really begin to address it. For
> example, with this patch applied, CPU idle is in single digits
> on the NFS server that exports the test's scratch device, and
> that server can still get into a soft lock-up. IMO that is
> because this change works around the underlying problem but
> makes no attempt to root-cause or address that issue.
> 
> I agree that the NFS server's behavior needs attention, but I'm
> not inclined to apply this particular patch as it is.

Yes. this patch is just particular for xfstests generic/531.

In xfstests  generic/531, when many(>500K ) files are kept as OPEN, a
file delete will cause LRU walk( CPU soft look-up) too.

big LRU data is still fast to add, but very slow to remove some random
one?

Best Regards
Wang Yugui (wangyugui@e16-tech.com)
2022/05/31