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Subject: Re: [PATCH 2/3] NFS: Allocate a scratch page for READ_PLUS
From:   Chuck Lever <chuck.lever@oracle.com>
In-Reply-To: <20201203201841.103294-3-Anna.Schumaker@Netapp.com>
Date:   Thu, 3 Dec 2020 15:27:08 -0500
Cc:     Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
        Anna Schumaker <Anna.Schumaker@Netapp.com>
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Message-Id: <8CE5CE8C-9301-4250-B077-ACE23969C19A@oracle.com>
References: <20201203201841.103294-1-Anna.Schumaker@Netapp.com>
 <20201203201841.103294-3-Anna.Schumaker@Netapp.com>
To:     Anna Schumaker <schumaker.anna@gmail.com>
Precedence: bulk


> On Dec 3, 2020, at 3:18 PM, schumaker.anna@gmail.com wrote:
>=20
> From: Anna Schumaker <Anna.Schumaker@Netapp.com>
>=20
> We might need this to better handle shifting around data in the reply
> buffer.
>=20
> Suggested-by: Trond Myklebust <trond.myklebust@hammerspace.com>
> Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
> ---
> fs/nfs/nfs42xdr.c       |  2 ++
> fs/nfs/read.c           | 13 +++++++++++--
> include/linux/nfs_xdr.h |  1 +
> 3 files changed, 14 insertions(+), 2 deletions(-)
>=20
> diff --git a/fs/nfs/nfs42xdr.c b/fs/nfs/nfs42xdr.c
> index 8432bd6b95f0..ef095a5f86f7 100644
> --- a/fs/nfs/nfs42xdr.c
> +++ b/fs/nfs/nfs42xdr.c
> @@ -1297,6 +1297,8 @@ static int nfs4_xdr_dec_read_plus(struct =
rpc_rqst *rqstp,
> 	struct compound_hdr hdr;
> 	int status;
>=20
> +	xdr_set_scratch_buffer(xdr, page_address(res->scratch), =
PAGE_SIZE);

I intend to submit this for v5.11:

=
https://git.linux-nfs.org/?p=3Dcel/cel-2.6.git;a=3Dcommit;h=3D0ae4c3e8a64a=
ce1b8d7de033b0751afe43024416

But seems like enough callers need a scratch buffer that the XDR
layer should set up it transparently for all requests.


> +
> 	status =3D decode_compound_hdr(xdr, &hdr);
> 	if (status)
> 		goto out;
> diff --git a/fs/nfs/read.c b/fs/nfs/read.c
> index eb854f1f86e2..012deb5a136f 100644
> --- a/fs/nfs/read.c
> +++ b/fs/nfs/read.c
> @@ -37,15 +37,24 @@ static struct kmem_cache *nfs_rdata_cachep;
>=20
> static struct nfs_pgio_header *nfs_readhdr_alloc(void)
> {
> -	struct nfs_pgio_header *p =3D =
kmem_cache_zalloc(nfs_rdata_cachep, GFP_KERNEL);
> +	struct nfs_pgio_header *p;
> +	struct page *page;
>=20
> -	if (p)
> +	page =3D alloc_page(GFP_KERNEL);
> +	if (!page)
> +		return ERR_PTR(-ENOMEM);
> +
> +	p =3D kmem_cache_zalloc(nfs_rdata_cachep, GFP_KERNEL);
> +	if (p) {
> 		p->rw_mode =3D FMODE_READ;
> +		p->res.scratch =3D page;
> +	}
> 	return p;
> }
>=20
> static void nfs_readhdr_free(struct nfs_pgio_header *rhdr)
> {
> +	__free_page(rhdr->res.scratch);
> 	kmem_cache_free(nfs_rdata_cachep, rhdr);
> }
>=20
> diff --git a/include/linux/nfs_xdr.h b/include/linux/nfs_xdr.h
> index d63cb862d58e..e0a1c97f11a9 100644
> --- a/include/linux/nfs_xdr.h
> +++ b/include/linux/nfs_xdr.h
> @@ -659,6 +659,7 @@ struct nfs_pgio_res {
> 	struct nfs_fattr *	fattr;
> 	__u64			count;
> 	__u32			op_status;
> +	struct page *		scratch;
> 	union {
> 		struct {
> 			unsigned int		replen;		/* used =
by read */
> --=20
> 2.29.2
>=20

--
Chuck Lever