Am Montag 05 Oktober 2009 21:30:39 schrieb Josef Bacik:
> Like the cluster allocating stuff, we can lockup the box with the normal
> allocation path. This happens when we
>
> 1) Start to cache a block group that is severely fragmented, but has a
> decent amount of free space.
> 2) Start to commit a transaction
> 3) Have the commit try and empty out some of the delalloc inodes with
> extents that are relatively large.
>
> The inodes will not be able to make the allocations because they will ask
> for allocations larger than a contiguous area in the free space cache. So
> we will wait for more progress to be made on the block group, but since
> we're in a commit the caching kthread won't make any more progress and it
> already has enough free space that wait_block_group_cache_progress will
> just return. So, if we wait and fail to make the allocation the next time
> around, just loop and go to the next block group. This keeps us from
> getting stuck in a softlockup. Thanks,
>
> Signed-off-by: Josef Bacik <jbacik@xxxxxxxxxx>
> ---
> fs/btrfs/extent-tree.c | 23 +++++++++++++++++------
> 1 files changed, 17 insertions(+), 6 deletions(-)
>
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index b259db3..e46b0b9 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -3816,6 +3816,7 @@ static noinline int find_free_extent(struct
> btrfs_trans_handle *trans, int loop = 0;
> bool found_uncached_bg = false;
> bool failed_cluster_refill = false;
> + bool failed_alloc = false;
>
> WARN_ON(num_bytes < root->sectorsize);
> btrfs_set_key_type(ins, BTRFS_EXTENT_ITEM_KEY);
> @@ -4020,14 +4021,23 @@ refill_cluster:
>
> offset = btrfs_find_space_for_alloc(block_group, search_start,
> num_bytes, empty_size);
> - if (!offset && (cached || (!cached &&
> - loop == LOOP_CACHING_NOWAIT))) {
> - goto loop;
> - } else if (!offset && (!cached &&
> - loop > LOOP_CACHING_NOWAIT)) {
> + /*
> + * If we didn't find a chunk, and we haven't failed on this
> + * block group before, and this block group is in the middle of
> + * caching and we are ok with waiting, then go ahead and wait
> + * for progress to be made, and set failed_alloc to true.
> + *
> + * If failed_alloc is true then we've already waited on this
> + * block group once and should move on to the next block group.
> + */
> + if (!offset && !failed_alloc && !cached &&
> + loop > LOOP_CACHING_NOWAIT) {
> wait_block_group_cache_progress(block_group,
> - num_bytes + empty_size);
> + num_bytes + empty_size);
> + failed_alloc = true;
> goto have_block_group;
> + } else if (!offset) {
> + goto loop;
> }
> checks:
> search_start = stripe_align(root, offset);
> @@ -4075,6 +4085,7 @@ checks:
> break;
> loop:
> failed_cluster_refill = false;
> + failed_alloc = false;
> btrfs_put_block_group(block_group);
> }
> up_read(&space_info->groups_sem);
>
My box survived 6h of dbench with this patch whereas without it hangs within
the first thwo minutes.
Johannes
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