Re: [PATCH RFC] nfs: optimise readdir cache page invalidation

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

On Thu, 2020-01-23 at 18:37 +0000, Trond Myklebust wrote:
> NetApp Security WARNING: This is an external email. Do not click links or open
> attachments unless you recognize the sender and know the content is safe.
> 
> 
> 
> 
> On Thu, 2020-01-23 at 10:35 -0800, Trond Myklebust wrote:
> > On Wed, 2020-01-22 at 18:48 -0500, Dai Ngo wrote:
> > > When the directory is large and it's being modified by one client
> > > while another client is doing the 'ls -l' on the same directory
> > > then
> > > the cache page invalidation from nfs_force_use_readdirplus causes
> > > the reading client to keep restarting READDIRPLUS from cookie 0
> > > which causes the 'ls -l' to take a very long time to complete,
> > > possibly never completing.
> > > 
> > > Currently when nfs_force_use_readdirplus is called to switch from
> > > READDIR to READDIRPLUS, it invalidates all the cached pages of the
> > > directory. This cache page invalidation causes the next nfs_readdir
> > > to re-read the directory content from cookie 0.
> > > 
> > > This patch is to optimise the cache invalidation in
> > > nfs_force_use_readdirplus by only truncating the cached pages from
> > > last page index accessed to the end the file. It also marks the
> > > inode to delay invalidating all the cached page of the directory
> > > until the next initial nfs_readdir of the next 'ls' instance.
> > > 
> > > Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
> > 
> > Reviewed-by: Trond Myklebust <trond.myklebust@hammerspace.com>
> 
> Sorry I intended this for the PATCHv2... I've looked through that
> version and it looks OK to me.
> 
> Anna, please apply the later v2 instead of this one...

I applied the v2 about 5 minutes before you sent this. I'll make sure your
Reviewed-by gets added to it, too :) 

Anna
> 
> > > ---
> > >  fs/nfs/dir.c           | 14 +++++++++++++-
> > >  include/linux/nfs_fs.h |  3 +++
> > >  2 files changed, 16 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
> > > index e180033e35cf..3fbf2e41d523 100644
> > > --- a/fs/nfs/dir.c
> > > +++ b/fs/nfs/dir.c
> > > @@ -437,7 +437,10 @@ void nfs_force_use_readdirplus(struct inode
> > > *dir)
> > >     if (nfs_server_capable(dir, NFS_CAP_READDIRPLUS) &&
> > >         !list_empty(&nfsi->open_files)) {
> > >             set_bit(NFS_INO_ADVISE_RDPLUS, &nfsi->flags);
> > > -           invalidate_mapping_pages(dir->i_mapping, 0, -1);
> > > +           nfs_zap_mapping(dir, dir->i_mapping);
> > > +           if (NFS_PROTO(dir)->version == 3)
> > > +                   invalidate_mapping_pages(dir->i_mapping,
> > > +                           nfsi->page_index + 1, -1);
> > >     }
> > >  }
> > > 
> > > @@ -709,6 +712,9 @@ struct page
> > > *get_cache_page(nfs_readdir_descriptor_t *desc)
> > >  int find_cache_page(nfs_readdir_descriptor_t *desc)
> > >  {
> > >     int res;
> > > +   struct inode *inode;
> > > +   struct nfs_inode *nfsi;
> > > +   struct dentry *dentry;
> > > 
> > >     desc->page = get_cache_page(desc);
> > >     if (IS_ERR(desc->page))
> > > @@ -717,6 +723,12 @@ int find_cache_page(nfs_readdir_descriptor_t
> > > *desc)
> > >     res = nfs_readdir_search_array(desc);
> > >     if (res != 0)
> > >             cache_page_release(desc);
> > > +
> > > +   dentry = file_dentry(desc->file);
> > > +   inode = d_inode(dentry);
> > > +   nfsi = NFS_I(inode);
> > > +   nfsi->page_index = desc->page_index;
> > > +
> > >     return res;
> > >  }
> > > 
> > > diff --git a/include/linux/nfs_fs.h b/include/linux/nfs_fs.h
> > > index c06b1fd130f3..a5f8f03ecd59 100644
> > > --- a/include/linux/nfs_fs.h
> > > +++ b/include/linux/nfs_fs.h
> > > @@ -168,6 +168,9 @@ struct nfs_inode {
> > >     struct rw_semaphore     rmdir_sem;
> > >     struct mutex            commit_mutex;
> > > 
> > > +   /* track last access to cached pages */
> > > +   unsigned long           page_index;
> > > +
> > >  #if IS_ENABLED(CONFIG_NFS_V4)
> > >     struct nfs4_cached_acl  *nfs4_acl;
> > >          /* NFSv4 state */
> --
> Trond Myklebust
> CTO, Hammerspace Inc
> 4300 El Camino Real, Suite 105
> Los Altos, CA 94022
> www.hammer.space
> 
>