2008/12/29 Liu Hui <onlyflyer@xxxxxxxxx>:
> Hi,
> This is a patch to fix discard semantic to make Btrfs work with FTL(or
> SSD?). As we know, we can improve FTL's performance by telling it
> which sectors are freed by file system. But if we don't tell FTL the
> information of free sectors in proper time, the transaction mechanism
> of Btrfs will be destroyed and Btrfs could not roll back the previous
> transaction under the power loss condition.
>
> There are some problems in the old implementation:
> 1, In __free_extent(), the pinned down extents should not be discarded.
> 2, In free_extents(), the free extents are all pinned, so they need to
> be discarded in transaction committing time instead of free_extents().
> 3, The reserved extent used by log tree should be discard too.
>
> This patch change discard behavior as follows:
> 1, In __free_extent, we only discard the unpinned extent.
> 2, Delay discarding the pinned extent in btrfs_finish_extent_commit()
> when committing transaction.
> 3, Remove discarding from free_extents()
> 4, Add discard interface into btrfs_free_reserved_extent()
> 5, Discard sectors before updating the free space cache, otherwise,
> FTL will destroy file system data.
>
> --
> Thanks & Best Regards
> Liu Hui
> --
Hi Liu Hui, your patch is malformed, please re-send it.
>
> diff --git a/extent-tree.c b/extent-tree.c
> index fe0e59a..7247b16 100644
> --- a/extent-tree.c
> +++ b/extent-tree.c
> @@ -874,6 +874,34 @@ static void btrfs_issue_discard(struct block_device *bdev,
> blkdev_issue_discard(bdev, start >> 9, len >> 9);
> #endif
> }
> +
> +static int btrfs_discard_extent(struct btrfs_root *root, u64 bytenr,
> + u64 num_bytes)
> +{
> + int ret;
> + u64 map_length = num_bytes;
> + struct btrfs_multi_bio *multi = NULL;
> +
> + /* Tell the block device(s) that the sectors can be discarded */
> + ret = btrfs_map_block(&root->fs_info->mapping_tree, READ,
> + bytenr, &map_length, &multi, 0);
> + if (!ret) {
> + struct btrfs_bio_stripe *stripe = multi->stripes;
> + int i;
> +
> + if (map_length > num_bytes)
> + map_length = num_bytes;
> +
> + for (i = 0; i < multi->num_stripes; i++, stripe++) {
> + btrfs_issue_discard(stripe->dev->bdev,
> + stripe->physical,
> + map_length);
> + }
> + kfree(multi);
> + }
> +
> + return ret;
> +}
> #endif
>
> static int noinline free_extents(struct btrfs_trans_handle *trans,
> @@ -1069,10 +1097,6 @@ search:
> for (pos = cur, n = pos->next; pos != end;
> pos = n, n = pos->next) {
> struct pending_extent_op *tmp;
> -#ifdef BIO_RW_DISCARD
> - u64 map_length;
> - struct btrfs_multi_bio *multi = NULL;
> -#endif
> tmp = list_entry(pos, struct pending_extent_op, list);
>
> /*
> @@ -1084,28 +1108,6 @@ search:
> tmp->del);
> BUG_ON(ret);
>
> -#ifdef BIO_RW_DISCARD
> - map_length = tmp->num_bytes;
> - ret = btrfs_map_block(&info->mapping_tree, READ,
> - tmp->bytenr, &map_length, &multi,
> - 0);
> - if (!ret) {
> - struct btrfs_bio_stripe *stripe;
> - int i;
> -
> - stripe = multi->stripes;
> -
> - if (map_length > tmp->num_bytes)
> - map_length = tmp->num_bytes;
> -
> - for (i = 0; i < multi->num_stripes;
> - i++, stripe++)
> - btrfs_issue_discard(stripe->dev->bdev,
> - stripe->physical,
> - map_length);
> - kfree(multi);
> - }
> -#endif
> list_del_init(&tmp->list);
> unlock_extent(&info->extent_ins, tmp->bytenr,
> tmp->bytenr + tmp->num_bytes - 1,
> @@ -2104,8 +2106,14 @@ int btrfs_finish_extent_commit(struct
> btrfs_trans_handle *trans,
> EXTENT_DIRTY);
> if (ret)
> break;
> +
> +#ifdef BIO_RW_DISCARD
> + ret = btrfs_discard_extent(root, start, end + 1 - start);
> +#endif
> +
> btrfs_update_pinned_extents(root, start, end + 1 - start, 0);
> clear_extent_dirty(unpin, start, end, GFP_NOFS);
> +
> if (need_resched()) {
> mutex_unlock(&root->fs_info->pinned_mutex);
> cond_resched();
> @@ -2113,7 +2121,7 @@ int btrfs_finish_extent_commit(struct
> btrfs_trans_handle *trans,
> }
> }
> mutex_unlock(&root->fs_info->pinned_mutex);
> - return 0;
> + return ret;
> }
>
> static int finish_current_insert(struct btrfs_trans_handle *trans,
> @@ -2458,10 +2466,6 @@ static int __free_extent(struct
> btrfs_trans_handle *trans,
> if (refs == 0) {
> u64 super_used;
> u64 root_used;
> -#ifdef BIO_RW_DISCARD
> - u64 map_length = num_bytes;
> - struct btrfs_multi_bio *multi = NULL;
> -#endif
>
> if (pin) {
> mutex_lock(&root->fs_info->pinned_mutex);
> @@ -2493,28 +2497,15 @@ static int __free_extent(struct
> btrfs_trans_handle *trans,
> BUG_ON(ret);
> }
>
> - ret = update_block_group(trans, root, bytenr, num_bytes, 0,
> - mark_free);
> - BUG_ON(ret);
> #ifdef BIO_RW_DISCARD
> - /* Tell the block device(s) that the sectors can be discarded */
> - ret = btrfs_map_block(&root->fs_info->mapping_tree, READ,
> - bytenr, &map_length, &multi, 0);
> - if (!ret) {
> - struct btrfs_bio_stripe *stripe = multi->stripes;
> - int i;
> -
> - if (map_length > num_bytes)
> - map_length = num_bytes;
> -
> - for (i = 0; i < multi->num_stripes; i++, stripe++) {
> - btrfs_issue_discard(stripe->dev->bdev,
> - stripe->physical,
> - map_length);
> - }
> - kfree(multi);
> + if (!pin) {
> + ret = btrfs_discard_extent(root, bytenr, num_bytes);
> }
We should check 'mark_free' instead of 'pin' here
> #endif
> +
> + ret = update_block_group(trans, root, bytenr, num_bytes, 0,
> + mark_free);
> + BUG_ON(ret);
> }
> btrfs_free_path(path);
> finish_current_insert(trans, extent_root, 0);
> @@ -3112,16 +3103,23 @@ again:
> int btrfs_free_reserved_extent(struct btrfs_root *root, u64 start, u64 len)
> {
> struct btrfs_block_group_cache *cache;
> + int ret = 0;
>
> cache = btrfs_lookup_block_group(root->fs_info, start);
> if (!cache) {
> printk(KERN_ERR "Unable to find block group for %Lu\n", start);
> return -ENOSPC;
> }
> +
> +#ifdef BIO_RW_DISCARD
> + ret = btrfs_discard_extent(root, start, len);
> +#endif
> +
> btrfs_add_free_space(cache, start, len);
> put_block_group(cache);
> update_reserved_extents(root, start, len, 0);
> - return 0;
> +
> + return ret;
> }
>
> int btrfs_reserve_extent(struct btrfs_trans_handle *trans,
--
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