On Mon, 13 Dec 2010 15:22:11 +0800 Shaohua Li <[email protected]> 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 <[email protected]> > > --- > 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 = { > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in > the body of a message to [email protected] > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
