On Mon, 13 Dec 2010 15:22:11 +0800
Shaohua Li <shaohua.li@xxxxxxxxx> wrote:
> Implement btrfs specific .metadata_incore.
> In btrfs, all metadata pages are in a special btree_inode, we take pages from it.
> we only account updated and referenced pages here. Say we collect metadata info
> in one boot, do metadata readahead in next boot and we might collect metadata
> again. The readahead could read garbage data in as metadata could be changed
> from first run. If we only account updated pages, the metadata info collected
> by userspace will increase every run. Btrfs alloc_extent_buffer will do
> mark_page_accessed() for pages which will be used soon, so we could use
> referenced bit to filter some garbage pages.
>
> Signed-off-by: Shaohua Li <shaohua.li@xxxxxxxxx>
>
> ---
> fs/btrfs/super.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 48 insertions(+)
>
> Index: linux/fs/btrfs/super.c
> ===================================================================
> --- linux.orig/fs/btrfs/super.c 2010-12-07 10:10:20.000000000 +0800
> +++ linux/fs/btrfs/super.c 2010-12-07 13:25:20.000000000 +0800
> @@ -39,6 +39,7 @@
> #include <linux/miscdevice.h>
> #include <linux/magic.h>
> #include <linux/slab.h>
> +#include <linux/pagevec.h>
> #include "compat.h"
> #include "ctree.h"
> #include "disk-io.h"
> @@ -845,6 +846,52 @@ static int btrfs_unfreeze(struct super_b
> return 0;
> }
>
> +static int btrfs_metadata_incore(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 pagevec pvec;
> + loff_t index = (*offset) >> PAGE_CACHE_SHIFT;
pgoff_t would be a more appropriate type.
> + int i, nr_pages;
> +
> + *size = 0;
> +retry:
> + pagevec_init(&pvec, 0);
> + nr_pages = pagevec_lookup(&pvec, btree_inode->i_mapping, index,
> + PAGEVEC_SIZE);
> + if (nr_pages == 0)
> + goto out;
> + for (i = 0; i < nr_pages; i++) {
> + struct page *page = pvec.pages[i];
> +
> + /* Only take pages with 'referenced' bit set */
The comment describes the utterly obvious and doesn't explain the
utterly unobvious: "why?".
> + if (PageUptodate(page) && PageReferenced(page)) {
> + if (*size == 0) {
> + *size += PAGE_CACHE_SIZE;
> + *offset = page->index << PAGE_CACHE_SHIFT;
> + continue;
> + }
> + if (page->index !=
> + (*offset + *size) >> PAGE_CACHE_SHIFT)
> + break;
> + *size += PAGE_CACHE_SIZE;
> + } else if (*size > 0)
> + break;
> + else
> + index = page->index + 1;
> + }
> + pagevec_release(&pvec);
> +
> + if (nr_pages > 0 && *size == 0)
> + goto retry;
I don't think I know why this retry loop exists. A comment would be
nice.
> +out:
> + if (*size > 0)
> + return 0;
> + else
> + return -ENOENT;
> +}
> +
> static const struct super_operations btrfs_super_ops = {
> .drop_inode = btrfs_drop_inode,
> .evict_inode = btrfs_evict_inode,
> @@ -859,6 +906,7 @@ static const struct super_operations btr
> .remount_fs = btrfs_remount,
> .freeze_fs = btrfs_freeze,
> .unfreeze_fs = btrfs_unfreeze,
> + .metadata_incore = btrfs_metadata_incore,
> };
>
> static const struct file_operations btrfs_ctl_fops = {
>
>
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