NFSD: Add experimental setting to disable the use of splice read

NFSD currently has two separate code paths for handling read
requests. One uses page splicing; the other is a traditional read
based on an iov iterator.

Because most Linux file systems support splice read, the latter
does not get nearly the same test experience as splice reads.

To force the use of vectored reads for testing and benchmarking,
introduce the ability to disable splice reads for all NFS READ
operations.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

diff --git a/fs/nfsd/debugfs.c b/fs/nfsd/debugfs.c
index e913268d9c2daa4fa635aeee043458a7e3bf9f2e..84b0c8b559dc90bd5c2d9d5e15c8e0682c0d610c 100644 (file)
--- a/fs/nfsd/debugfs.c
+++ b/fs/nfsd/debugfs.c
@@ -6,6 +6,32 @@
 
 static struct dentry *nfsd_top_dir __read_mostly;
 
+/*
+ * /sys/kernel/debug/nfsd/disable-splice-read
+ *
+ * Contents:
+ *   %0: NFS READ is allowed to use page splicing
+ *   %1: NFS READ uses only iov iter read
+ *
+ * The default value of this setting is zero (page splicing is
+ * allowed). This setting takes immediate effect for all NFS
+ * versions, all exports, and in all NFSD net namespaces.
+ */
+
+static int nfsd_dsr_get(void *data, u64 *val)
+{
+       *val = nfsd_disable_splice_read ? 1 : 0;
+       return 0;
+}
+
+static int nfsd_dsr_set(void *data, u64 val)
+{
+       nfsd_disable_splice_read = (val > 0) ? true : false;
+       return 0;
+}
+
+DEFINE_DEBUGFS_ATTRIBUTE(nfsd_dsr_fops, nfsd_dsr_get, nfsd_dsr_set, "%llu\n");
+
 void nfsd_debugfs_exit(void)
 {
        debugfs_remove_recursive(nfsd_top_dir);
@@ -15,4 +41,7 @@ void nfsd_debugfs_exit(void)
 void nfsd_debugfs_init(void)
 {
        nfsd_top_dir = debugfs_create_dir("nfsd", NULL);
+
+       debugfs_create_file("disable-splice-read", S_IWUSR | S_IRUGO,
+                           nfsd_top_dir, NULL, &nfsd_dsr_fops);
 }

diff --git a/fs/nfsd/nfsd.h b/fs/nfsd/nfsd.h
index 8a53ddab5df011d0f7b868859b6fc720c99eee66..232aee06223d59642233a75a9efe2471e2ac3b11 100644 (file)
--- a/fs/nfsd/nfsd.h
+++ b/fs/nfsd/nfsd.h
@@ -164,6 +164,8 @@ static inline void nfsd_debugfs_init(void) {}
 static inline void nfsd_debugfs_exit(void) {}
 #endif
 
+extern bool nfsd_disable_splice_read __read_mostly;
+
 extern int nfsd_max_blksize;
 
 static inline int nfsd_v4client(struct svc_rqst *rq)

diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 9abdc4b758138be025ae1d88eb5f91f4f00b114a..02827b0f0492d20f010151d5bd860ef509fb643f 100644 (file)
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -47,6 +47,8 @@
 
 #define NFSDDBG_FACILITY               NFSDDBG_FILEOP
 
+bool nfsd_disable_splice_read __read_mostly;
+
 /**
  * nfserrno - Map Linux errnos to NFS errnos
  * @errno: POSIX(-ish) error code to be mapped
@@ -1236,6 +1238,8 @@ out_nfserr:
  */
 bool nfsd_read_splice_ok(struct svc_rqst *rqstp)
 {
+       if (nfsd_disable_splice_read)
+               return false;
        switch (svc_auth_flavor(rqstp)) {
        case RPC_AUTH_GSS_KRB5I:
        case RPC_AUTH_GSS_KRB5P: