Re: [PATCH v2 1/1] NFS: Convert from readpages() to readahead()

[David Wysochanski <dwysocha@redhat.com>]

On Wed, Oct 20, 2021 at 3:27 PM Trond Myklebust <trondmy@hammerspace.com> wrote:
>
> On Sat, 2021-10-09 at 08:36 -0400, Dave Wysochanski wrote:
> > Convert to the new VM readahead() API which is the preferred API
> > to read multiple pages, and rename the NFSIOS_* counters and the
> > tracepoint as needed.
> >
> > Signed-off-by: Dave Wysochanski <dwysocha@redhat.com>
> > ---
> >  fs/nfs/file.c              |  2 +-
> >  fs/nfs/read.c              | 18 +++++++++++++-----
> >  include/linux/nfs_fs.h     |  3 +--
> >  include/linux/nfs_iostat.h |  6 +++---
> >  4 files changed, 18 insertions(+), 11 deletions(-)
> >
> > diff --git a/fs/nfs/file.c b/fs/nfs/file.c
> > index 209dac208477..cc76d17fa97f 100644
> > --- a/fs/nfs/file.c
> > +++ b/fs/nfs/file.c
> > @@ -519,7 +519,7 @@ static void nfs_swap_deactivate(struct file
> > *file)
> >
> >  const struct address_space_operations nfs_file_aops = {
> >         .readpage = nfs_readpage,
> > -       .readpages = nfs_readpages,
> > +       .readahead = nfs_readahead,
> >         .set_page_dirty = __set_page_dirty_nobuffers,
> >         .writepage = nfs_writepage,
> >         .writepages = nfs_writepages,
> > diff --git a/fs/nfs/read.c b/fs/nfs/read.c
> > index d06b91a101d2..296ea9a9b6ce 100644
> > --- a/fs/nfs/read.c
> > +++ b/fs/nfs/read.c
> > @@ -397,15 +397,19 @@ int nfs_readpage(struct file *file, struct page
> > *page)
> >         return ret;
> >  }
> >
> > -int nfs_readpages(struct file *file, struct address_space *mapping,
> > -               struct list_head *pages, unsigned nr_pages)
> > +void nfs_readahead(struct readahead_control *ractl)
> >  {
> > +       struct file *file = ractl->file;
> > +       struct address_space *mapping = ractl->mapping;
> > +       struct page *page;
> > +       unsigned int nr_pages = readahead_count(ractl);
> > +
> >         struct nfs_readdesc desc;
> >         struct inode *inode = mapping->host;
> >         int ret;
> >
> >         trace_nfs_aop_readahead(inode, nr_pages);
> > -       nfs_inc_stats(inode, NFSIOS_VFSREADPAGES);
> > +       nfs_inc_stats(inode, NFSIOS_VFSREADAHEAD);
> >
> >         ret = -ESTALE;
> >         if (NFS_STALE(inode))
> > @@ -422,14 +426,18 @@ int nfs_readpages(struct file *file, struct
> > address_space *mapping,
>
>
> This function fails to compile due to the call to
> nfs_readpages_from_fscache() taking a 'pages' argument.
>

Sorry about the confusion.  See the "PATCH 0/1" description [1].
This patch as posted assumes dhowells "fallback API" series.
Are you ok with that series, or do you still have concerns?

I am not sure if I can redo this patch without that series but I can
try if you're opposed to the fallback API series or see problems
such as merging conflicts or want this patch only for some reason.

Let me know what you want and I'll try to make it happen.

[1] https://marc.info/?l=linux-nfs&m=163378294028491&w=2




> >         nfs_pageio_init_read(&desc.pgio, inode, false,
> >                              &nfs_async_read_completion_ops);
> >
> > -       ret = read_cache_pages(mapping, pages, readpage_async_filler,
> > &desc);
> > +       ret = 0;
> > +       while (!ret && (page = readahead_page(ractl))) {
> > +               prefetchw(&page->flags);
> > +               ret = readpage_async_filler(&desc, page);
> > +               put_page(page);
> > +       }
> >
> >         nfs_pageio_complete_read(&desc.pgio);
> >
> >         put_nfs_open_context(desc.ctx);
> >  out:
> >         trace_nfs_aop_readahead_done(inode, nr_pages, ret);
> > -       return ret;
> >  }
> >
> >  int __init nfs_init_readpagecache(void)
> > diff --git a/include/linux/nfs_fs.h b/include/linux/nfs_fs.h
> > index 140187b57db8..a5aef2cbe4ee 100644
> > --- a/include/linux/nfs_fs.h
> > +++ b/include/linux/nfs_fs.h
> > @@ -586,8 +586,7 @@ extern int nfs_access_get_cached(struct inode
> > *inode, const struct cred *cred, s
> >   * linux/fs/nfs/read.c
> >   */
> >  extern int  nfs_readpage(struct file *, struct page *);
> > -extern int  nfs_readpages(struct file *, struct address_space *,
> > -               struct list_head *, unsigned);
> > +extern void nfs_readahead(struct readahead_control *);
> >
> >  /*
> >   * inline functions
> > diff --git a/include/linux/nfs_iostat.h b/include/linux/nfs_iostat.h
> > index 027874c36c88..418145f23700 100644
> > --- a/include/linux/nfs_iostat.h
> > +++ b/include/linux/nfs_iostat.h
> > @@ -22,7 +22,7 @@
> >  #ifndef _LINUX_NFS_IOSTAT
> >  #define _LINUX_NFS_IOSTAT
> >
> > -#define NFS_IOSTAT_VERS                "1.1"
> > +#define NFS_IOSTAT_VERS                "1.2"
> >
> >  /*
> >   * NFS byte counters
> > @@ -53,7 +53,7 @@
> >   * NFS page counters
> >   *
> >   * These count the number of pages read or written via
> > nfs_readpage(),
> > - * nfs_readpages(), or their write equivalents.
> > + * nfs_readahead(), or their write equivalents.
> >   *
> >   * NB: When adding new byte counters, please include the measured
> >   * units in the name of each byte counter to help users of this
> > @@ -98,7 +98,7 @@ enum nfs_stat_eventcounters {
> >         NFSIOS_VFSACCESS,
> >         NFSIOS_VFSUPDATEPAGE,
> >         NFSIOS_VFSREADPAGE,
> > -       NFSIOS_VFSREADPAGES,
> > +       NFSIOS_VFSREADAHEAD,
> >         NFSIOS_VFSWRITEPAGE,
> >         NFSIOS_VFSWRITEPAGES,
> >         NFSIOS_VFSGETDENTS,
>
> --
> Trond Myklebust
> Linux NFS client maintainer, Hammerspace
> trond.myklebust@hammerspace.com
>
>