This is a note to let you know that I've just added the patch titled
NFSD: Restore NFSv4 decoding's SAVEMEM functionality
to the 5.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
nfsd-restore-nfsv4-decoding-s-savemem-functionality.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 73f02d3487433849118444ee45fb6c249fcadcb0
Author: Chuck Lever <chuck.lever@xxxxxxxxxx>
Date: Fri Dec 18 12:28:58 2020 -0500
NFSD: Restore NFSv4 decoding's SAVEMEM functionality
[ Upstream commit 7b723008f9c95624c848fad661c01b06e47b20da ]
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 <chuck.lever@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index bb037e8eb8304..8d5fdae568aeb 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);
}
