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

["Yan, Zheng" <zheng.z.yan@linux.intel.com>]

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.

Yan, Zheng
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