> On Jun 17, 2021, at 7:26 PM, trondmy@xxxxxxxxxx wrote:
>
> From: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
>
> When flushing out the unstable file writes as part of a COMMIT call, try
> to perform most of of the data writes and waits outside the semaphore.
>
> This means that if the client is sending the COMMIT as part of a memory
> reclaim operation, then it can continue performing I/O, with contention
> for the lock occurring only once the data sync is finished.
>
> Fixes: 5011af4c698a ("nfsd: Fix stable writes")
> Signed-off-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
I can see write throughput improvement now.
Tested-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
This is NFSv3 against an NVMe-backed XFS export, wsize=8192:
v5.13-rc6:
Command line used: /home/cel/bin/iozone -M -+u -i0 -i1 -s1g -r256k -t12 -I
Output is in kBytes/sec
Time Resolution = 0.000001 seconds.
Processor cache size set to 1024 kBytes.
Processor cache line size set to 32 bytes.
File stride size set to 17 * record size.
Throughput test with 12 processes
Each process writes a 1048576 kByte file in 256 kByte records
Children see throughput for 12 initial writers = 416004.59 kB/sec
Parent sees throughput for 12 initial writers = 415691.65 kB/sec
Min throughput per process = 34630.36 kB/sec
Max throughput per process = 34703.62 kB/sec
Avg throughput per process = 34667.05 kB/sec
Min xfer = 1046528.00 kB
CPU Utilization: Wall time 30.239 CPU time 5.854 CPU utilization 19.36 %
Children see throughput for 12 rewriters = 516605.59 kB/sec
Parent sees throughput for 12 rewriters = 516530.05 kB/sec
Min throughput per process = 43007.56 kB/sec
Max throughput per process = 43074.50 kB/sec
Avg throughput per process = 43050.47 kB/sec
Min xfer = 1047040.00 kB
CPU utilization: Wall time 24.347 CPU time 5.882 CPU utilization 24.16 %
v5.13-rc6 + Trond's patch:
Command line used: /home/cel/bin/iozone -M -+u -i0 -i1 -s1g -r256k -t12 -I
Output is in kBytes/sec
Time Resolution = 0.000001 seconds.
Processor cache size set to 1024 kBytes.
Processor cache line size set to 32 bytes.
File stride size set to 17 * record size.
Throughput test with 12 processes
Each process writes a 1048576 kByte file in 256 kByte records
Children see throughput for 12 initial writers = 434971.09 kB/sec
Parent sees throughput for 12 initial writers = 434649.13 kB/sec
Min throughput per process = 36209.41 kB/sec
Max throughput per process = 36287.55 kB/sec
Avg throughput per process = 36247.59 kB/sec
Min xfer = 1046528.00 kB
CPU Utilization: Wall time 28.920 CPU time 5.705 CPU utilization 19.73 %
Children see throughput for 12 rewriters = 544700.37 kB/sec
Parent sees throughput for 12 rewriters = 544623.91 kB/sec
Min throughput per process = 45320.82 kB/sec
Max throughput per process = 45456.07 kB/sec
Avg throughput per process = 45391.70 kB/sec
Min xfer = 1045504.00 kB
CPU utilization: Wall time 23.071 CPU time 5.708 CPU utilization 24.74 %
> ---
> fs/nfsd/vfs.c | 18 ++++++++++++++++--
> 1 file changed, 16 insertions(+), 2 deletions(-)
>
> diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
> index 15adf1f6ab21..46485c04740d 100644
> --- a/fs/nfsd/vfs.c
> +++ b/fs/nfsd/vfs.c
> @@ -1123,6 +1123,19 @@ nfsd_write(struct svc_rqst *rqstp, struct svc_fh *fhp, loff_t offset,
> }
>
> #ifdef CONFIG_NFSD_V3
> +static int
> +nfsd_filemap_write_and_wait_range(struct nfsd_file *nf, loff_t offset,
> + loff_t end)
> +{
> + struct address_space *mapping = nf->nf_file->f_mapping;
> + int ret = filemap_fdatawrite_range(mapping, offset, end);
> +
> + if (ret)
> + return ret;
> + filemap_fdatawait_range_keep_errors(mapping, offset, end);
> + return 0;
> +}
> +
> /*
> * Commit all pending writes to stable storage.
> *
> @@ -1153,10 +1166,11 @@ nfsd_commit(struct svc_rqst *rqstp, struct svc_fh *fhp,
> if (err)
> goto out;
> if (EX_ISSYNC(fhp->fh_export)) {
> - int err2;
> + int err2 = nfsd_filemap_write_and_wait_range(nf, offset, end);
>
> down_write(&nf->nf_rwsem);
> - err2 = vfs_fsync_range(nf->nf_file, offset, end, 0);
> + if (!err2)
> + err2 = vfs_fsync_range(nf->nf_file, offset, end, 0);
> switch (err2) {
> case 0:
> nfsd_copy_boot_verifier(verf, net_generic(nf->nf_net,
> --
> 2.31.1
>
--
Chuck Lever
