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It may be enabled with: >> echo Y > /sys/module/nfsd/parameters/nfsd_dontcache >> >> FOP_DONTCACHE must be advertised as supported by the underlying >> filesystem (e.g. XFS), otherwise if/when 'nfsd_dontcache' is enabled >> all IO will fail with -EOPNOTSUPP. >> > > A little more explanation here would be good. What problem is this > solving? In general we don't go for tunables like this unless there is > just no alternative. > > What might help me understand this is to add some documentation that > explains when an admin would want to enable this. Agreed: I might know why this is interesting, since Mike and I discussed it during bake-a-thon. But other reviewers don't, so it would be helpful to provide a little more context in the patch description. >> Signed-off-by: Mike Snitzer >> --- >> fs/nfsd/vfs.c | 17 ++++++++++++++++- >> 1 file changed, 16 insertions(+), 1 deletion(-) >> >> diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c >> index 29cb7b812d71..d7e49004e93d 100644 >> --- a/fs/nfsd/vfs.c >> +++ b/fs/nfsd/vfs.c >> @@ -955,6 +955,11 @@ nfsd_open_verified(struct svc_fh *fhp, int may_flags, struct file **filp) >> return __nfsd_open(fhp, S_IFREG, may_flags, filp); >> } >> >> +static bool nfsd_dontcache __read_mostly = false; >> +module_param(nfsd_dontcache, bool, 0644); >> +MODULE_PARM_DESC(nfsd_dontcache, >> + "Any data read or written by nfsd will be removed from the page cache upon completion."); >> + >> /* >> * Grab and keep cached pages associated with a file in the svc_rqst >> * so that they can be passed to the network sendmsg routines >> @@ -1084,6 +1089,7 @@ __be32 nfsd_iter_read(struct svc_rqst *rqstp, struct svc_fh *fhp, >> loff_t ppos = offset; >> struct page *page; >> ssize_t host_err; >> + rwf_t flags = 0; >> >> v = 0; >> total = *count; >> @@ -1097,9 +1103,12 @@ __be32 nfsd_iter_read(struct svc_rqst *rqstp, struct svc_fh *fhp, >> } >> WARN_ON_ONCE(v > ARRAY_SIZE(rqstp->rq_vec)); >> >> + if (nfsd_dontcache) >> + flags |= RWF_DONTCACHE; >> + >> trace_nfsd_read_vector(rqstp, fhp, offset, *count); >> iov_iter_kvec(&iter, ITER_DEST, rqstp->rq_vec, v, *count); >> - host_err = vfs_iter_read(file, &iter, &ppos, 0); >> + host_err = vfs_iter_read(file, &iter, &ppos, flags); >> return nfsd_finish_read(rqstp, fhp, file, offset, count, eof, host_err); >> } >> >> @@ -1186,6 +1195,9 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp, struct nfsd_file *nf, >> if (stable && !fhp->fh_use_wgather) >> flags |= RWF_SYNC; >> >> + if (nfsd_dontcache) >> + flags |= RWF_DONTCACHE; >> + >> iov_iter_kvec(&iter, ITER_SOURCE, vec, vlen, *cnt); >> since = READ_ONCE(file->f_wb_err); >> if (verf) >> @@ -1237,6 +1249,9 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp, struct nfsd_file *nf, >> */ >> bool nfsd_read_splice_ok(struct svc_rqst *rqstp) >> { >> + if (nfsd_dontcache) /* force the use of vfs_iter_read for reads */ >> + return false; >> + >> switch (svc_auth_flavor(rqstp)) { >> case RPC_AUTH_GSS_KRB5I: >> case RPC_AUTH_GSS_KRB5P: > -- Chuck Lever