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nfscl: Use vfs.nfs.maxalloclen to limit Deallocate RPC RTT

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Unlike Copy, the NFSv4.2 Allocate and Deallocate operations do not
allow a reply with partial completion.  As such, the only way to
limit the time the operation takes to provide a reasonable RPC RTT
is to limit the size of the allocation/deallocation in the NFSv4.2
client.

This patch uses the sysctl vfs.nfs.maxalloclen to set
the limit on the size of the Deallocate operation.
There is no way to know how long a server will take to do an
deallocate operation, but 64Mbytes results in a reasonable
RPC RTT for the slow hardware I test on.

For an 8Gbyte deallocation, the elapsed time for doing it in 64Mbyte
chunks was the same (within margin of variability) as the
elapsed time taken for a single large deallocation
operation for a FreeBSD server with a UFS file system.
This commit is contained in:
Rick Macklem 2021-09-18 14:38:43 -07:00
parent 7b2ac8eb9b
commit ad6dc36520
1 changed files with 18 additions and 2 deletions
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20
sys/fs/nfsclient/nfs_clvnops.c
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@ -3702,12 +3702,15 @@ nfs_deallocate(struct vop_deallocate_args *ap)
struct thread *td = curthread;
struct nfsvattr nfsva;
struct nfsmount *nmp;
off_t tlen;
struct nfsnode *np;
off_t tlen, mlen;
int attrflag, error, ret;
bool clipped;
error = 0;
attrflag = 0;
nmp = VFSTONFS(vp->v_mount);
np = VTONFS(vp);
mtx_lock(&nmp->nm_mtx);
if (NFSHASNFSV4(nmp) && nmp->nm_minorvers >= NFSV42_MINORVERSION &&
(nmp->nm_privflag & NFSMNTP_NODEALLOCATE) == 0) {
@ -3721,8 +3724,18 @@ nfs_deallocate(struct vop_deallocate_args *ap)
*ap->a_len = 0;
return (0);
}
clipped = false;
if ((uint64_t)*ap->a_offset + tlen > nmp->nm_maxfilesize)
tlen = nmp->nm_maxfilesize - *ap->a_offset;
if ((uint64_t)*ap->a_offset < np->n_size) {
/* Limit the len to nfs_maxalloclen before EOF. */
mlen = omin((off_t)np->n_size - *ap->a_offset, tlen);
if ((uint64_t)mlen > nfs_maxalloclen) {
NFSCL_DEBUG(4, "dealloc: tlen maxalloclen\n");
tlen = nfs_maxalloclen;
clipped = true;
}
}
if (error == 0)
error = ncl_vinvalbuf(vp, V_SAVE, td, 1);
if (error == 0) {
@ -3741,7 +3754,10 @@ nfs_deallocate(struct vop_deallocate_args *ap)
nfsva.na_size - *ap->a_offset,
tlen);
}
*ap->a_len = 0;
if (clipped && tlen < *ap->a_len)
*ap->a_len -= tlen;
else
*ap->a_len = 0;
} else if (error == NFSERR_NOTSUPP) {
mtx_lock(&nmp->nm_mtx);
nmp->nm_privflag |= NFSMNTP_NODEALLOCATE;