On Fri, Oct 12, 2018 at 02:18:19PM +0800, Qu Wenruo wrote:
> We have a complex loop design for find_free_extent(), that has different
> behavior for each loop, some even includes new chunk allocation.
>
> Instead of putting such a long code into find_free_extent() and makes it
> harder to read, just extract them into find_free_extent_update_loop().
>
> With all the cleanups, the main find_free_extent() should be pretty
> barebone:
>
> find_free_extent()
> |- Iterate through all block groups
> | |- Get a valid block group
> | |- Try to do clustered allocation in that block group
> | |- Try to do unclustered allocation in that block group
> | |- Check if the result is valid
> | | |- If valid, then exit
> | |- Jump to next block group
> |
> |- Push harder to find free extents
> |- If not found, re-iterate all block groups
>
> Signed-off-by: Qu Wenruo <wqu@xxxxxxxx>
> Reviewed-by: Su Yue <suy.fnst@xxxxxxxxxxxxxx>
> ---
> fs/btrfs/extent-tree.c | 217 ++++++++++++++++++++++-------------------
> 1 file changed, 117 insertions(+), 100 deletions(-)
>
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index e6bfa91af41c..938569d2c583 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -7236,7 +7236,9 @@ struct find_free_extent_ctl {
> /* RAID index, converted from flags */
> int index;
>
> - /* Current loop number */
> + /*
> + * Current loop number, check find_free_extent_update_loop() for details
> + */
> int loop;
>
> /*
> @@ -7433,6 +7435,117 @@ static int find_free_extent_unclustered(struct btrfs_block_group_cache *bg,
> return 0;
> }
>
> +/*
> + * Return >0 means caller needs to re-search for free extent
> + * Return 0 means we have the needed free extent.
> + * Return <0 means we failed to locate any free extent.
> + */
> +static int find_free_extent_update_loop(struct btrfs_fs_info *fs_info,
> + struct btrfs_free_cluster *last_ptr,
> + struct btrfs_key *ins,
> + struct find_free_extent_ctl *ffe_ctl,
> + int full_search, bool use_cluster)
> +{
> + struct btrfs_root *root = fs_info->extent_root;
> + int ret;
> +
> + if ((ffe_ctl->loop == LOOP_CACHING_NOWAIT) &&
> + ffe_ctl->have_caching_bg && !ffe_ctl->orig_have_caching_bg)
> + ffe_ctl->orig_have_caching_bg = true;
> +
> + if (!ins->objectid && ffe_ctl->loop >= LOOP_CACHING_WAIT &&
> + ffe_ctl->have_caching_bg)
> + return 1;
> +
> + if (!ins->objectid && ++(ffe_ctl->index) < BTRFS_NR_RAID_TYPES)
> + return 1;
> +
> + /*
> + * LOOP_CACHING_NOWAIT, search partially cached block groups, kicking
> + * caching kthreads as we move along
> + * LOOP_CACHING_WAIT, search everything, and wait if our bg is caching
> + * LOOP_ALLOC_CHUNK, force a chunk allocation and try again
> + * LOOP_NO_EMPTY_SIZE, set empty_size and empty_cluster to 0 and try
> + * again
> + */
> + if (!ins->objectid && ffe_ctl->loop < LOOP_NO_EMPTY_SIZE) {
> + ffe_ctl->index = 0;
> + if (ffe_ctl->loop == LOOP_CACHING_NOWAIT) {
> + /*
> + * We want to skip the LOOP_CACHING_WAIT step if we
> + * don't have any uncached bgs and we've already done a
> + * full search through.
> + */
> + if (ffe_ctl->orig_have_caching_bg || !full_search)
> + ffe_ctl->loop = LOOP_CACHING_WAIT;
> + else
> + ffe_ctl->loop = LOOP_ALLOC_CHUNK;
> + } else {
> + ffe_ctl->loop++;
> + }
> +
> + if (ffe_ctl->loop == LOOP_ALLOC_CHUNK) {
> + struct btrfs_trans_handle *trans;
> + int exist = 0;
> +
> + trans = current->journal_info;
> + if (trans)
> + exist = 1;
> + else
> + trans = btrfs_join_transaction(root);
> +
> + if (IS_ERR(trans)) {
> + ret = PTR_ERR(trans);
> + return ret;
> + }
> +
> + ret = do_chunk_alloc(trans, ffe_ctl->flags,
> + CHUNK_ALLOC_FORCE);
> +
> + /*
> + * If we can't allocate a new chunk we've already looped
> + * through at least once, move on to the NO_EMPTY_SIZE
> + * case.
> + */
> + if (ret == -ENOSPC)
> + ffe_ctl->loop = LOOP_NO_EMPTY_SIZE;
> +
> + /* Do not bail out on ENOSPC since we can do more. */
> + if (ret < 0 && ret != -ENOSPC)
> + btrfs_abort_transaction(trans, ret);
> + else
> + ret = 0;
> + if (!exist)
> + btrfs_end_transaction(trans);
> + if (ret)
> + return ret;
> + }
> +
> + if (ffe_ctl->loop == LOOP_NO_EMPTY_SIZE) {
> + /*
> + * Don't loop again if we already have no empty_size and
> + * no empty_cluster.
> + */
> + if (ffe_ctl->empty_size == 0 &&
> + ffe_ctl->empty_cluster == 0)
> + return -ENOSPC;
> + ffe_ctl->empty_size = 0;
> + ffe_ctl->empty_cluster = 0;
> + }
> + return 1;
> + } else if (!ins->objectid) {
> + ret = -ENOSPC;
> + } else if (ins->objectid) {
> + if (!use_cluster && last_ptr) {
> + spin_lock(&last_ptr->lock);
> + last_ptr->window_start = ins->objectid;
> + spin_unlock(&last_ptr->lock);
> + }
> + ret = 0;
> + }
> + return ret;
> +}
Rework this so the
if (ins->objectid)
blah
is the first thing, that way you don't have to do the
if (!ins->objectid && <other things>)
for all the other if statements here. The fast path should be the first thing,
then we can deal with all of the other crap last. Thanks,
Josef
