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

[Trond Myklebust <trondmy@hammerspace.com>]

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...

> 
> > ---
> >  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