From: Charles Hedrick <hedrick@rutgers.edu>
To: "linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>
Subject: optimization for nfsd_set_fh_dentry
Date: Sun, 7 Apr 2024 13:25:33 +0000 [thread overview]
Message-ID: <PH0PR14MB549329F998F7DB972744F45FAA012@PH0PR14MB5493.namprd14.prod.outlook.com> (raw)
nfsd_set_fh_dentry is used in setfh and a number of other places. It calls exportfs_decode_fh_raw with an argument nfsd_acceptable.
That is a test that always returns 1 if NFSEXP_NOSUBTREECHECK is set.
However there is an optimization in exportfs_decode_fh_raw that skips a lot of file system stuff if NULL is passed as the test. A test that always returns 1 still triggers all the file system stuff, even though it's not needed.
nfsd_set_fh_dentry should pass NULL to exportfs_decode_fh_raw if NFSEXP_NOSUBTREECHECK is set.
I discovered this while looking into a performance problem caused by a pathological client that was sending 40,000 RPCs/sec, almost all get
GETATTR or ACCESS. It was causing the nfsd's to be stuck at 100% CPU by locks in file system code invoked by this unnecessary code.
(We fixed the client by mounting with NFS3 rather than NFS4. This suggests an issue with the NFS 4 client side. Unfortunately I don't have enough information to make a useful report.)
next reply other threads:[~2024-04-07 13:25 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-07 13:25 Charles Hedrick [this message]
2024-04-08 11:51 ` optimization for nfsd_set_fh_dentry Charles Hedrick
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