Re: [RFC 4/5] implement metadata_ra in btrfs

[Shaohua Li <shaohua.li@intel.com>]

On Tue, 2010-12-14 at 09:06 +0800, Yan, Zheng wrote:
> On Mon, Dec 13, 2010 at 3:22 PM, Shaohua Li <shaohua.li@intel.com> wrote:
> > Implementation btrfs .metadata_readahead. In btrfs, all metadata pages are in a
> > special btree_inode. We do readahead in it.
> >
> > Signed-off-by: Shaohua Li <shaohua.li@intel.com>
> >
> > ---
> >  fs/btrfs/disk-io.c |   10 ++++++++++
> >  fs/btrfs/super.c   |   13 +++++++++++++
> >  mm/readahead.c     |    1 +
> >  3 files changed, 24 insertions(+)
> >
> > Index: linux/fs/btrfs/disk-io.c
> > ===================================================================
> > --- linux.orig/fs/btrfs/disk-io.c       2010-12-07 13:32:24.000000000 +0800
> > +++ linux/fs/btrfs/disk-io.c    2010-12-07 13:33:08.000000000 +0800
> > @@ -776,6 +776,15 @@ static int btree_readpage(struct file *f
> >        return extent_read_full_page(tree, page, btree_get_extent);
> >  }
> >
> > +static int btree_readpages(struct file *file, struct address_space *mapping,
> > +               struct list_head *pages, unsigned nr_pages)
> > +{
> > +       struct extent_io_tree *tree;
> > +       tree = &BTRFS_I(mapping->host)->io_tree;
> > +       return extent_readpages(tree, mapping, pages, nr_pages,
> > +                       btree_get_extent);
> > +}
> > +
> >  static int btree_releasepage(struct page *page, gfp_t gfp_flags)
> >  {
> >        struct extent_io_tree *tree;
> > @@ -819,6 +828,7 @@ static void btree_invalidatepage(struct
> >
> >  static const struct address_space_operations btree_aops = {
> >        .readpage       = btree_readpage,
> > +       .readpages      = btree_readpages,
> >        .writepage      = btree_writepage,
> >        .writepages     = btree_writepages,
> >        .releasepage    = btree_releasepage,
> > Index: linux/fs/btrfs/super.c
> > ===================================================================
> > --- linux.orig/fs/btrfs/super.c 2010-12-07 13:32:24.000000000 +0800
> > +++ linux/fs/btrfs/super.c      2010-12-07 13:33:08.000000000 +0800
> > @@ -892,6 +892,18 @@ out:
> >                return -ENOENT;
> >  }
> >
> > +static int btrfs_metadata_readahead(struct super_block *sb, loff_t offset,
> > +       ssize_t size)
> > +{
> > +       struct btrfs_root *tree_root = btrfs_sb(sb);
> > +       struct inode *btree_inode = tree_root->fs_info->btree_inode;
> > +       struct address_space *mapping = btree_inode->i_mapping;
> > +
> > +       force_page_cache_readahead(mapping, NULL, offset >> PAGE_CACHE_SHIFT,
> > +               size >> PAGE_CACHE_SHIFT);
> > +       return 0;
> > +}
> > +
> >  static const struct super_operations btrfs_super_ops = {
> >        .drop_inode     = btrfs_drop_inode,
> >        .evict_inode    = btrfs_evict_inode,
> > @@ -907,6 +919,7 @@ static const struct super_operations btr
> >        .freeze_fs      = btrfs_freeze,
> >        .unfreeze_fs    = btrfs_unfreeze,
> >        .metadata_incore = btrfs_metadata_incore,
> > +       .metadata_readahead = btrfs_metadata_readahead,
> >  };
> >
> >  static const struct file_operations btrfs_ctl_fops = {
> > Index: linux/mm/readahead.c
> > ===================================================================
> > --- linux.orig/mm/readahead.c   2010-12-07 13:32:24.000000000 +0800
> > +++ linux/mm/readahead.c        2010-12-07 13:33:08.000000000 +0800
> > @@ -228,6 +228,7 @@ int force_page_cache_readahead(struct ad
> >        }
> >        return ret;
> >  }
> > +EXPORT_SYMBOL_GPL(force_page_cache_readahead);
> >
> >  /*
> >  * Given a desired number of PAGE_CACHE_SIZE readahead pages, return a
> >
> >
> 
> btrfs will crash If the read-ahead range falls into unallocated chunk.
> need code to check validity of the user input.
didn't hit this, maybe I'm lucky. I'll double check this.

Thanks,
Shaohua