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[68.61.232.219]) by smtp.gmail.com with ESMTPSA id f59sm36997208qtd.84.2021.01.04.04.42.38 for (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Mon, 04 Jan 2021 04:42:38 -0800 (PST) Sender: Chuck Lever Received: from klimt.1015granger.net (klimt.1015granger.net [192.168.1.55]) by gateway.1015granger.net (8.14.7/8.14.7) with ESMTP id 104CgbFB017706 for ; Mon, 4 Jan 2021 12:42:37 GMT Subject: [PATCH] NFSD: Restore NFSv4 decoding's SAVEMEM functionality From: Chuck Lever To: linux-nfs@vger.kernel.org Date: Mon, 04 Jan 2021 07:42:37 -0500 Message-ID: <160976412038.1233.502071259496733128.stgit@klimt.1015granger.net> User-Agent: StGit/0.23-29-ga622f1 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org While converting the NFSv4 decoder to use xdr_stream-based XDR processing, I removed the old SAVEMEM() macro. This macro wrapped a bit of logic that avoided a memory allocation by recognizing when the decoded item resides in a linear section of the Receive buffer. In that case, it returned a pointer into that buffer instead of allocating a bounce buffer. The bounce buffer is necessary only when xdr_inline_decode() has placed the decoded item in the xdr_stream's scratch buffer, which disappears the next time xdr_inline_decode() is called with that xdr_stream. That happens only if the data item crosses a page boundary in the receive buffer, an exceedingly rare occurrence. Allocating a bounce buffer every time results in a minor performance regression that was introduced by the recent NFSv4 decoder overhaul. Let's restore the previous behavior. On average, it saves about 1.5 kmalloc() calls per COMPOUND. Signed-off-by: Chuck Lever --- fs/nfsd/nfs4xdr.c | 42 ++++++++++++++++++++++++++---------------- 1 file changed, 26 insertions(+), 16 deletions(-) Hi- I intend to include this with the first NFSD v5.11-rc pull request. diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c index 20178f60f612..eaaa1605b5b5 100644 --- a/fs/nfsd/nfs4xdr.c +++ b/fs/nfsd/nfs4xdr.c @@ -147,6 +147,25 @@ svcxdr_dupstr(struct nfsd4_compoundargs *argp, void *buf, u32 len) return p; } +static void * +svcxdr_savemem(struct nfsd4_compoundargs *argp, __be32 *p, u32 len) +{ + __be32 *tmp; + + /* + * The location of the decoded data item is stable, + * so @p is OK to use. This is the common case. + */ + if (p != argp->xdr->scratch.iov_base) + return p; + + tmp = svcxdr_tmpalloc(argp, len); + if (!tmp) + return NULL; + memcpy(tmp, p, len); + return tmp; +} + /* * NFSv4 basic data type decoders */ @@ -183,11 +202,10 @@ nfsd4_decode_opaque(struct nfsd4_compoundargs *argp, struct xdr_netobj *o) p = xdr_inline_decode(argp->xdr, len); if (!p) return nfserr_bad_xdr; - o->data = svcxdr_tmpalloc(argp, len); + o->data = svcxdr_savemem(argp, p, len); if (!o->data) return nfserr_jukebox; o->len = len; - memcpy(o->data, p, len); return nfs_ok; } @@ -205,10 +223,9 @@ nfsd4_decode_component4(struct nfsd4_compoundargs *argp, char **namp, u32 *lenp) status = check_filename((char *)p, *lenp); if (status) return status; - *namp = svcxdr_tmpalloc(argp, *lenp); + *namp = svcxdr_savemem(argp, p, *lenp); if (!*namp) return nfserr_jukebox; - memcpy(*namp, p, *lenp); return nfs_ok; } @@ -1200,10 +1217,9 @@ nfsd4_decode_putfh(struct nfsd4_compoundargs *argp, struct nfsd4_putfh *putfh) p = xdr_inline_decode(argp->xdr, putfh->pf_fhlen); if (!p) return nfserr_bad_xdr; - putfh->pf_fhval = svcxdr_tmpalloc(argp, putfh->pf_fhlen); + putfh->pf_fhval = svcxdr_savemem(argp, p, putfh->pf_fhlen); if (!putfh->pf_fhval) return nfserr_jukebox; - memcpy(putfh->pf_fhval, p, putfh->pf_fhlen); return nfs_ok; } @@ -1318,24 +1334,20 @@ nfsd4_decode_setclientid(struct nfsd4_compoundargs *argp, struct nfsd4_setclient p = xdr_inline_decode(argp->xdr, setclientid->se_callback_netid_len); if (!p) return nfserr_bad_xdr; - setclientid->se_callback_netid_val = svcxdr_tmpalloc(argp, + setclientid->se_callback_netid_val = svcxdr_savemem(argp, p, setclientid->se_callback_netid_len); if (!setclientid->se_callback_netid_val) return nfserr_jukebox; - memcpy(setclientid->se_callback_netid_val, p, - setclientid->se_callback_netid_len); if (xdr_stream_decode_u32(argp->xdr, &setclientid->se_callback_addr_len) < 0) return nfserr_bad_xdr; p = xdr_inline_decode(argp->xdr, setclientid->se_callback_addr_len); if (!p) return nfserr_bad_xdr; - setclientid->se_callback_addr_val = svcxdr_tmpalloc(argp, + setclientid->se_callback_addr_val = svcxdr_savemem(argp, p, setclientid->se_callback_addr_len); if (!setclientid->se_callback_addr_val) return nfserr_jukebox; - memcpy(setclientid->se_callback_addr_val, p, - setclientid->se_callback_addr_len); if (xdr_stream_decode_u32(argp->xdr, &setclientid->se_callback_ident) < 0) return nfserr_bad_xdr; @@ -1375,10 +1387,9 @@ nfsd4_decode_verify(struct nfsd4_compoundargs *argp, struct nfsd4_verify *verify p = xdr_inline_decode(argp->xdr, verify->ve_attrlen); if (!p) return nfserr_bad_xdr; - verify->ve_attrval = svcxdr_tmpalloc(argp, verify->ve_attrlen); + verify->ve_attrval = svcxdr_savemem(argp, p, verify->ve_attrlen); if (!verify->ve_attrval) return nfserr_jukebox; - memcpy(verify->ve_attrval, p, verify->ve_attrlen); return nfs_ok; } @@ -2333,10 +2344,9 @@ nfsd4_decode_compound(struct nfsd4_compoundargs *argp) p = xdr_inline_decode(argp->xdr, argp->taglen); if (!p) return 0; - argp->tag = svcxdr_tmpalloc(argp, argp->taglen); + argp->tag = svcxdr_savemem(argp, p, argp->taglen); if (!argp->tag) return 0; - memcpy(argp->tag, p, argp->taglen); max_reply += xdr_align_size(argp->taglen); }