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From:   Chuck Lever III <chuck.lever@oracle.com>
To:     Al Viro <viro@zeniv.linux.org.uk>
CC:     Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
        netdev <netdev@vger.kernel.org>,
        Dave Chinner <david@fromorbit.com>,
        "tgraf@suug.ch" <tgraf@suug.ch>, Jeff Layton <jlayton@redhat.com>
Subject: Re: [PATCH RFC 28/30] NFSD: Set up an rhashtable for the filecache
Thread-Topic: [PATCH RFC 28/30] NFSD: Set up an rhashtable for the filecache
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Date:   Thu, 23 Jun 2022 23:51:29 +0000
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> On Jun 23, 2022, at 6:56 PM, Al Viro <viro@zeniv.linux.org.uk> wrote:
>=20
> On Wed, Jun 22, 2022 at 10:15:50AM -0400, Chuck Lever wrote:
>=20
>> +static u32 nfsd_file_obj_hashfn(const void *data, u32 len, u32 seed)
>> +{
>> +	const struct nfsd_file *nf =3D data;
>> +
>> +	return jhash2((const u32 *)&nf->nf_inode,
>> +		      sizeof_field(struct nfsd_file, nf_inode) / sizeof(u32),
>> +		      seed);
>=20
> Out of curiosity - what are you using to allocate those?  Because if
> it's a slab, then middle bits of address (i.e. lower bits of
> (unsigned long)data / L1_CACHE_BYTES) would better be random enough...

 261 static struct nfsd_file *
 262 nfsd_file_alloc(struct nfsd_file_lookup_key *key, unsigned int may)
 263 {
 264         static atomic_t nfsd_file_id;
 265         struct nfsd_file *nf;
 266=20
 267         nf =3D kmem_cache_alloc(nfsd_file_slab, GFP_KERNEL);

Was wondering about that. pahole says struct nfsd_file is 112
bytes on my system.


--
Chuck Lever