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btrfs: use readahead API for scrub
Scrub uses a simple tree-enumeration to bring the relevant portions of the extent- and csum-tree into the page cache before starting the scrub-I/O. This is now replaced by using the new readahead-API. During readahead the scrub is being accounted as paused, so it won't hold off transaction commits. This change raises the average disk bandwith utilisation on my test volume from 70% to 90%. On another volume, the time for a test run went down from 89s to 43s. Changes v5: - reada1/2 are now of type struct reada_control * Signed-off-by: Arne Jansen <sensille@gmx.net>
This commit is contained in:
parent
4bb31e928d
commit
7a26285eea
1 changed files with 48 additions and 60 deletions
108
fs/btrfs/scrub.c
108
fs/btrfs/scrub.c
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@ -29,15 +29,12 @@
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* any can be found.
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*
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* Future enhancements:
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* - To enhance the performance, better read-ahead strategies for the
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* extent-tree can be employed.
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* - In case an unrepairable extent is encountered, track which files are
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* affected and report them
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* - In case of a read error on files with nodatasum, map the file and read
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* the extent to trigger a writeback of the good copy
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* - track and record media errors, throw out bad devices
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* - add a mode to also read unallocated space
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* - make the prefetch cancellable
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*/
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struct scrub_bio;
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@ -741,13 +738,16 @@ static noinline_for_stack int scrub_stripe(struct scrub_dev *sdev,
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int slot;
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int i;
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u64 nstripes;
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int start_stripe;
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struct extent_buffer *l;
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struct btrfs_key key;
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u64 physical;
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u64 logical;
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u64 generation;
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u64 mirror_num;
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struct reada_control *reada1;
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struct reada_control *reada2;
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struct btrfs_key key_start;
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struct btrfs_key key_end;
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u64 increment = map->stripe_len;
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u64 offset;
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@ -779,81 +779,67 @@ static noinline_for_stack int scrub_stripe(struct scrub_dev *sdev,
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if (!path)
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return -ENOMEM;
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path->reada = 2;
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path->search_commit_root = 1;
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path->skip_locking = 1;
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/*
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* find all extents for each stripe and just read them to get
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* them into the page cache
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* FIXME: we can do better. build a more intelligent prefetching
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* trigger the readahead for extent tree csum tree and wait for
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* completion. During readahead, the scrub is officially paused
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* to not hold off transaction commits
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*/
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logical = base + offset;
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physical = map->stripes[num].physical;
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ret = 0;
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for (i = 0; i < nstripes; ++i) {
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key.objectid = logical;
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key.type = BTRFS_EXTENT_ITEM_KEY;
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key.offset = (u64)0;
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ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
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if (ret < 0)
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goto out_noplug;
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wait_event(sdev->list_wait,
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atomic_read(&sdev->in_flight) == 0);
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atomic_inc(&fs_info->scrubs_paused);
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wake_up(&fs_info->scrub_pause_wait);
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/*
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* we might miss half an extent here, but that doesn't matter,
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* as it's only the prefetch
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*/
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while (1) {
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l = path->nodes[0];
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slot = path->slots[0];
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if (slot >= btrfs_header_nritems(l)) {
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ret = btrfs_next_leaf(root, path);
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if (ret == 0)
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continue;
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if (ret < 0)
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goto out_noplug;
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/* FIXME it might be better to start readahead at commit root */
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key_start.objectid = logical;
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key_start.type = BTRFS_EXTENT_ITEM_KEY;
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key_start.offset = (u64)0;
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key_end.objectid = base + offset + nstripes * increment;
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key_end.type = BTRFS_EXTENT_ITEM_KEY;
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key_end.offset = (u64)0;
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reada1 = btrfs_reada_add(root, &key_start, &key_end);
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break;
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}
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btrfs_item_key_to_cpu(l, &key, slot);
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key_start.objectid = BTRFS_EXTENT_CSUM_OBJECTID;
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key_start.type = BTRFS_EXTENT_CSUM_KEY;
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key_start.offset = logical;
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key_end.objectid = BTRFS_EXTENT_CSUM_OBJECTID;
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key_end.type = BTRFS_EXTENT_CSUM_KEY;
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key_end.offset = base + offset + nstripes * increment;
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reada2 = btrfs_reada_add(csum_root, &key_start, &key_end);
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if (key.objectid >= logical + map->stripe_len)
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break;
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if (!IS_ERR(reada1))
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btrfs_reada_wait(reada1);
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if (!IS_ERR(reada2))
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btrfs_reada_wait(reada2);
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path->slots[0]++;
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}
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btrfs_release_path(path);
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logical += increment;
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physical += map->stripe_len;
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cond_resched();
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mutex_lock(&fs_info->scrub_lock);
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while (atomic_read(&fs_info->scrub_pause_req)) {
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mutex_unlock(&fs_info->scrub_lock);
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wait_event(fs_info->scrub_pause_wait,
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atomic_read(&fs_info->scrub_pause_req) == 0);
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mutex_lock(&fs_info->scrub_lock);
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}
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atomic_dec(&fs_info->scrubs_paused);
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mutex_unlock(&fs_info->scrub_lock);
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wake_up(&fs_info->scrub_pause_wait);
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/*
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* collect all data csums for the stripe to avoid seeking during
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* the scrub. This might currently (crc32) end up to be about 1MB
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*/
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start_stripe = 0;
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blk_start_plug(&plug);
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again:
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logical = base + offset + start_stripe * increment;
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for (i = start_stripe; i < nstripes; ++i) {
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ret = btrfs_lookup_csums_range(csum_root, logical,
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logical + map->stripe_len - 1,
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&sdev->csum_list, 1);
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if (ret)
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goto out;
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logical += increment;
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cond_resched();
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}
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/*
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* now find all extents for each stripe and scrub them
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*/
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logical = base + offset + start_stripe * increment;
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physical = map->stripes[num].physical + start_stripe * map->stripe_len;
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logical = base + offset;
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physical = map->stripes[num].physical;
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ret = 0;
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for (i = start_stripe; i < nstripes; ++i) {
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for (i = 0; i < nstripes; ++i) {
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/*
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* canceled?
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*/
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@ -882,11 +868,14 @@ static noinline_for_stack int scrub_stripe(struct scrub_dev *sdev,
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atomic_dec(&fs_info->scrubs_paused);
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mutex_unlock(&fs_info->scrub_lock);
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wake_up(&fs_info->scrub_pause_wait);
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scrub_free_csums(sdev);
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start_stripe = i;
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goto again;
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}
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ret = btrfs_lookup_csums_range(csum_root, logical,
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logical + map->stripe_len - 1,
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&sdev->csum_list, 1);
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if (ret)
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goto out;
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key.objectid = logical;
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key.type = BTRFS_EXTENT_ITEM_KEY;
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key.offset = (u64)0;
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@ -982,7 +971,6 @@ static noinline_for_stack int scrub_stripe(struct scrub_dev *sdev,
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out:
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blk_finish_plug(&plug);
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out_noplug:
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btrfs_free_path(path);
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return ret < 0 ? ret : 0;
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}
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