Re: [PATCH 7/7] NFS: Add a mount option for READ_PLUS

["Schumaker, Anna" <Anna.Schumaker@netapp.com>]

Hi Chuck,

On Fri, 2020-01-10 at 17:41 -0500, Chuck Lever wrote:
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> 
> 
> 
> Hi Anna-
> 
> > On Jan 10, 2020, at 5:34 PM, schumaker.anna@gmail.com wrote:
> > 
> > From: Anna Schumaker <Anna.Schumaker@Netapp.com>
> > 
> > There are some workloads where READ_PLUS might end up hurting
> > performance,
> 
> Can you say more about this? Have you seen workloads that are
> hurt by READ_PLUS? Nothing jumps out at me from the tables in
> the cover letter.

It's mostly something I've seen when using btrfs in a virtual machine (so
probably not a wide use case, and it's possible I need to change something in my
setup to get it working better).

> 
> 
> > so let's be nice to users and provide a way to disable this
> > operation similar to how READDIR_PLUS can be disabled.
> 
> Does it make sense to hold off on a mount option until there
> is evidence that there is no other way to work around such a
> performance regression?
> 
> - Attempt to address the regression directly
> - Improve the heuristics about when READ_PLUS is used
> - Document that dropping back to vers=4.1 will disable it

Yeah, we could hold off on the patch for now and see if anybody has any issues
first.

> 
> Any experience with NFS/RDMA?

Not yet, but I can try to test that next week.

Anna

> 
> 
> > Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
> > ---
> > fs/nfs/fs_context.c       | 14 ++++++++++++++
> > fs/nfs/nfs4client.c       |  3 +++
> > include/linux/nfs_fs_sb.h |  1 +
> > 3 files changed, 18 insertions(+)
> > 
> > diff --git a/fs/nfs/fs_context.c b/fs/nfs/fs_context.c
> > index 0247dcb7b316..82ba07c7c1ce 100644
> > --- a/fs/nfs/fs_context.c
> > +++ b/fs/nfs/fs_context.c
> > @@ -64,6 +64,7 @@ enum nfs_param {
> >       Opt_proto,
> >       Opt_rdirplus,
> >       Opt_rdma,
> > +     Opt_readplus,
> >       Opt_resvport,
> >       Opt_retrans,
> >       Opt_retry,
> > @@ -120,6 +121,7 @@ static const struct fs_parameter_spec nfs_param_specs[]
> > = {
> >       fsparam_string("proto",         Opt_proto),
> >       fsparam_flag_no("rdirplus",     Opt_rdirplus),
> >       fsparam_flag  ("rdma",          Opt_rdma),
> > +     fsparam_flag_no("readplus",     Opt_readplus),
> >       fsparam_flag_no("resvport",     Opt_resvport),
> >       fsparam_u32   ("retrans",       Opt_retrans),
> >       fsparam_string("retry",         Opt_retry),
> > @@ -555,6 +557,12 @@ static int nfs_fs_context_parse_param(struct fs_context
> > *fc,
> >               else
> >                       ctx->options |= NFS_OPTION_MIGRATION;
> >               break;
> > +     case Opt_readplus:
> > +             if (result.negated)
> > +                     ctx->options |= NFS_OPTION_NO_READ_PLUS;
> > +             else
> > +                     ctx->options &= ~NFS_OPTION_NO_READ_PLUS;
> > +             break;
> > 
> >               /*
> >                * options that take numeric values
> > @@ -1176,6 +1184,10 @@ static int nfs_fs_context_validate(struct fs_context
> > *fc)
> >           (ctx->version != 4 || ctx->minorversion != 0))
> >               goto out_migration_misuse;
> > 
> > +     if (ctx->options & NFS_OPTION_NO_READ_PLUS &&
> > +         (ctx->version != 4 || ctx->minorversion < 2))
> > +             goto out_noreadplus_misuse;
> > +
> >       /* Verify that any proto=/mountproto= options match the address
> >        * families in the addr=/mountaddr= options.
> >        */
> > @@ -1254,6 +1266,8 @@ static int nfs_fs_context_validate(struct fs_context
> > *fc)
> >                         ctx->version, ctx->minorversion);
> > out_migration_misuse:
> >       return nfs_invalf(fc, "NFS: 'Migration' not supported for this NFS
> > version");
> > +out_noreadplus_misuse:
> > +     return nfs_invalf(fc, "NFS: 'noreadplus' not supported for this NFS
> > version\n");
> > out_version_unavailable:
> >       nfs_errorf(fc, "NFS: Version unavailable");
> >       return ret;
> > diff --git a/fs/nfs/nfs4client.c b/fs/nfs/nfs4client.c
> > index 0cd767e5c977..868dc3c36ba1 100644
> > --- a/fs/nfs/nfs4client.c
> > +++ b/fs/nfs/nfs4client.c
> > @@ -1016,6 +1016,9 @@ static int nfs4_server_common_setup(struct nfs_server
> > *server,
> >       server->caps |= server->nfs_client->cl_mvops->init_caps;
> >       if (server->flags & NFS_MOUNT_NORDIRPLUS)
> >                       server->caps &= ~NFS_CAP_READDIRPLUS;
> > +     if (server->options & NFS_OPTION_NO_READ_PLUS)
> > +             server->caps &= ~NFS_CAP_READ_PLUS;
> > +
> >       /*
> >        * Don't use NFS uid/gid mapping if we're using AUTH_SYS or lower
> >        * authentication.
> > diff --git a/include/linux/nfs_fs_sb.h b/include/linux/nfs_fs_sb.h
> > index 11248c5a7b24..360e70c7bbb6 100644
> > --- a/include/linux/nfs_fs_sb.h
> > +++ b/include/linux/nfs_fs_sb.h
> > @@ -172,6 +172,7 @@ struct nfs_server {
> >       unsigned int            clone_blksize;  /* granularity of a CLONE
> > operation */
> > #define NFS_OPTION_FSCACHE    0x00000001      /* - local caching enabled */
> > #define NFS_OPTION_MIGRATION  0x00000002      /* - NFSv4 migration enabled
> > */
> > +#define NFS_OPTION_NO_READ_PLUS      0x00000004      /* - NFSv4.2 READ_PLUS
> > enabled */
> > 
> >       struct nfs_fsid         fsid;
> >       __u64                   maxfilesize;    /* maximum file size */
> > --
> > 2.24.1
> > 
> 
> --
> Chuck Lever
> 
> 
>