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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>
pull/1112/head
Chuck Lever 2025-03-08 15:14:38 -05:00
parent 9fe5ea760e
commit 1218149037
3 changed files with 35 additions and 0 deletions
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29
fs/nfsd/debugfs.c
View File

@ -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);
}

2
fs/nfsd/nfsd.h
View File

@ -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)

4
fs/nfsd/vfs.c
View File

@ -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: