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From:   Chuck Lever III <chuck.lever@oracle.com>
To:     Wang Yugui <wangyugui@e16-tech.com>
CC:     Chuck Lever <cel@kernel.org>, Jeff Layton <jlayton@redhat.com>,
        Neil Brown <neilb@suse.de>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>
Subject: Re: [PATCH RFC] NFSD: Convert filecache to rhltable
Thread-Topic: [PATCH RFC] NFSD: Convert filecache to rhltable
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Date:   Fri, 6 Jan 2023 14:13:24 +0000
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> On Jan 6, 2023, at 1:00 AM, Wang Yugui <wangyugui@e16-tech.com> wrote:
>=20
> Hi,
>=20
>> From: Chuck Lever <chuck.lever@oracle.com>
>>=20
>> While we were converting the nfs4_file hashtable to use the kernel's
>> resizable hashtable data structure, Neil Brown observed that the
>> list variant (rhltable) would be better for managing nfsd_file items
>> as well. The nfsd_file hash table will contain multiple entries for
>> the same inode -- these should be kept together on a list. And, it
>> could be possible for exotic or malicious client behavior to cause
>> the hash table to resize itself on every insertion.
>>=20
>> A nice simplification is that rhltable_lookup() can return a list
>> that contains only nfsd_file items that match a given inode, which
>> enables us to eliminate specialized hash table helper functions and
>> use the default functions provided by the rhashtable implementation).
>>=20
>> Since we are now storing nfsd_file items for the same inode on a
>> single list, that effectively reduces the number of hash entries
>> that have to be tracked in the hash table. The mininum bucket count
>> is therefore lowered.
>=20
> some bench result such as fstests generic/531 maybe useful.

Sure. I don't expect there will be much change, but one never knows.


> And this patch conflict with another patch:
> (v3) [PATCH] nfsd: fix handling of cached open files in nfsd4_open codepa=
th

Yes, this is known to conflict with patches that are now in flight.
I'll rebase once those are merged.


--
Chuck Lever