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nfscl: Add a "has acquired a delegation" flag for delegations

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A problem was reported via email, where a large (130000+) accumulation
of NFSv4 opens on an NFSv4 mount caused significant lock contention
on the mutex used to protect the client mount's open/lock state.
Although the root cause for the accumulation of opens was not
resolved, it is obvious that the NFSv4 client is not designed to
handle 100000+ opens efficiently.

For a common case where delegations are not being issued by the
NFSv4 server, the code acquires the mutex lock for open/lock state,
finds the delegation list empty and just unlocks the mutex and returns.
This patch adds an NFS mount point flag that is set when a delegation
is issued for the mount.  Then the patched code checks for this flag
before acquiring the open/lock mutex, avoiding the need to acquire
the lock for the case where delegations are not being issued by the
NFSv4 server.
This change appears to be performance neutral for a small number
of opens, but should reduce lock contention for a large number of opens
for the common case where server is not issuing delegations.

This commit should not affect the high level semantics of delegation
handling.

MFC after:      2 weeks
This commit is contained in:
Rick Macklem 2021-06-09 08:00:43 -07:00
parent 334335cb14
commit 5e5ca4c8fc
2 changed files with 42 additions and 3 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

44
sys/fs/nfsclient/nfs_clstate.c
View file

@ -438,20 +438,32 @@ nfscl_deleg(mount_t mp, struct nfsclclient *clp, u_int8_t *nfhp,
int fhlen, struct ucred *cred, NFSPROC_T *p, struct nfscldeleg **dpp)
{
struct nfscldeleg *dp = *dpp, *tdp;
struct nfsmount *nmp;
KASSERT(mp != NULL, ("nfscl_deleg: mp NULL"));
nmp = VFSTONFS(mp);
/*
* First, if we have received a Read delegation for a file on a
* read/write file system, just return it, because they aren't
* useful, imho.
*/
if (mp != NULL && dp != NULL && !NFSMNT_RDONLY(mp) &&
if (dp != NULL && !NFSMNT_RDONLY(mp) &&
(dp->nfsdl_flags & NFSCLDL_READ)) {
(void) nfscl_trydelegreturn(dp, cred, VFSTONFS(mp), p);
nfscl_trydelegreturn(dp, cred, nmp, p);
free(dp, M_NFSCLDELEG);
*dpp = NULL;
return (0);
}
/*
* Since a delegation might be added to the mount,
* set NFSMNTP_DELEGISSUED now. If a delegation already
* exagain ists, setting this flag is harmless.
*/
NFSLOCKMNT(nmp);
nmp->nm_privflag |= NFSMNTP_DELEGISSUED;
NFSUNLOCKMNT(nmp);
/* Look for the correct deleg, based upon FH */
NFSLOCKCLSTATE();
tdp = nfscl_finddeleg(clp, nfhp, fhlen);
@ -3356,12 +3368,20 @@ nfscl_delegreturnvp(vnode_t vp, NFSPROC_T *p)
struct nfscldeleg *dp;
struct ucred *cred;
struct nfsnode *np;
struct nfsmount *nmp;
nmp = VFSTONFS(vp->v_mount);
NFSLOCKMNT(nmp);
if ((nmp->nm_privflag & NFSMNTP_DELEGISSUED) == 0) {
NFSUNLOCKMNT(nmp);
return;
}
NFSUNLOCKMNT(nmp);
np = VTONFS(vp);
cred = newnfs_getcred();
dp = NULL;
NFSLOCKCLSTATE();
clp = VFSTONFS(vp->v_mount)->nm_clp;
clp = nmp->nm_clp;
if (clp != NULL)
dp = nfscl_finddeleg(clp, np->n_fhp->nfh_fh,
np->n_fhp->nfh_len);
@ -4500,6 +4520,12 @@ nfscl_nodeleg(vnode_t vp, int writedeleg)
nmp = VFSTONFS(vp->v_mount);
if (!NFSHASNFSV4(nmp))
return (1);
NFSLOCKMNT(nmp);
if ((nmp->nm_privflag & NFSMNTP_DELEGISSUED) == 0) {
NFSUNLOCKMNT(nmp);
return (1);
}
NFSUNLOCKMNT(nmp);
NFSLOCKCLSTATE();
clp = nfscl_findcl(nmp);
if (clp == NULL) {
@ -4856,6 +4882,12 @@ nfscl_delegmodtime(vnode_t vp)
nmp = VFSTONFS(vp->v_mount);
if (!NFSHASNFSV4(nmp))
return;
NFSLOCKMNT(nmp);
if ((nmp->nm_privflag & NFSMNTP_DELEGISSUED) == 0) {
NFSUNLOCKMNT(nmp);
return;
}
NFSUNLOCKMNT(nmp);
NFSLOCKCLSTATE();
clp = nfscl_findcl(nmp);
if (clp == NULL) {
@ -4885,6 +4917,12 @@ nfscl_deleggetmodtime(vnode_t vp, struct timespec *mtime)
nmp = VFSTONFS(vp->v_mount);
if (!NFSHASNFSV4(nmp))
return;
NFSLOCKMNT(nmp);
if ((nmp->nm_privflag & NFSMNTP_DELEGISSUED) == 0) {
NFSUNLOCKMNT(nmp);
return;
}
NFSUNLOCKMNT(nmp);
NFSLOCKCLSTATE();
clp = nfscl_findcl(nmp);
if (clp == NULL) {

1
sys/fs/nfsclient/nfsmount.h
View file

@ -115,6 +115,7 @@ struct nfsmount {
#define NFSMNTP_NOXATTR 0x00000080
#define NFSMNTP_NOADVISE 0x00000100
#define NFSMNTP_NOALLOCATE 0x00000200
#define NFSMNTP_DELEGISSUED 0x00000400
/* New mount flags only used by the kernel via nmount(2). */
#define NFSMNT_TLS 0x00000001