Re: [PATCH] nfsd: Reduce contention for the nfsd_file nf_rwsem

[Chuck Lever III <chuck.lever@oracle.com>]

Hi-

> On Jun 17, 2021, at 7:26 PM, trondmy@kernel.org wrote:
> 
> From: Trond Myklebust <trond.myklebust@hammerspace.com>
> 
> 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@hammerspace.com>

The good news is I've found no functional regressions. The bad
news is I haven't seen any difference in performance. Is there
a particular test that I can run to observe improvement?

I wonder about adding a Fixes: tag for a change that the patch
description describes as an optimization.


> ---
> 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