On Fri, Mar 19, 2021 at 10:52 AM Johannes Thumshirn
<johannes.thumsh...@wdc.com> wrote:
>
> When a file gets deleted on a zoned file system, the space freed is not
> returned back into the block group's free space, but is migrated to
> zone_unusable.
>
> As this zone_unusable space is behind the current write pointer it is not
> possible to use it for new allocations. In the current implementation a
> zone is reset once all of the block group's space is accounted as zone
> unusable.
>
> This behaviour can lead to premature ENOSPC errors on a busy file system.
>
> Instead of only reclaiming the zone once it is completely unusable,
> kick off a reclaim job once the amount of unusable bytes exceeds a user
> configurable threshold between 51% and 100%. It can be set per mounted
> filesystem via the sysfs tunable bg_reclaim_threshold which is set to 75%
> per default.
>
> Similar to reclaiming unused block groups, these dirty block groups are
> added to a to_reclaim list and then on a transaction commit, the reclaim
> process is triggered but after we deleted unused block groups, which will
> free space for the relocation process.
>
> Signed-off-by: Johannes Thumshirn <johannes.thumsh...@wdc.com>
> ---
>
> AFAICT sysfs_create_files() does not have the ability to provide a is_visible
> callback, so the bg_reclaim_threshold sysfs file is visible for non zoned
> filesystems as well, even though only for zoned filesystems we're adding block
> groups to the reclaim list. I'm all ears for a approach that is sensible in
> this regard.
>
>
> fs/btrfs/block-group.c | 84 ++++++++++++++++++++++++++++++++++++
> fs/btrfs/block-group.h | 2 +
> fs/btrfs/ctree.h | 3 ++
> fs/btrfs/disk-io.c | 11 +++++
> fs/btrfs/free-space-cache.c | 9 +++-
> fs/btrfs/sysfs.c | 35 +++++++++++++++
> fs/btrfs/volumes.c | 2 +-
> fs/btrfs/volumes.h | 1 +
> include/trace/events/btrfs.h | 12 ++++++
> 9 files changed, 157 insertions(+), 2 deletions(-)
>
> diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
> index 9ae3ac96a521..af9026795ddd 100644
> --- a/fs/btrfs/block-group.c
> +++ b/fs/btrfs/block-group.c
> @@ -1485,6 +1485,80 @@ void btrfs_mark_bg_unused(struct btrfs_block_group *bg)
> spin_unlock(&fs_info->unused_bgs_lock);
> }
>
> +void btrfs_reclaim_bgs(struct btrfs_fs_info *fs_info)
> +{
> + struct btrfs_block_group *bg;
> + struct btrfs_space_info *space_info;
> + int ret = 0;
> +
> + if (!test_bit(BTRFS_FS_OPEN, &fs_info->flags))
> + return;
> +
> + if (!btrfs_exclop_start(fs_info, BTRFS_EXCLOP_BALANCE))
> + return;
> +
> + mutex_lock(&fs_info->reclaim_bgs_lock);
> + while (!list_empty(&fs_info->reclaim_bgs)) {
> + bg = list_first_entry(&fs_info->reclaim_bgs,
> + struct btrfs_block_group,
> + bg_list);
> + list_del_init(&bg->bg_list);
> +
> + space_info = bg->space_info;
> + mutex_unlock(&fs_info->reclaim_bgs_lock);
> +
> + /* Don't want to race with allocators so take the groups_sem
> */
> + down_write(&space_info->groups_sem);
> +
> + spin_lock(&bg->lock);
> + if (bg->reserved || bg->pinned || bg->ro) {
> + /*
> + * We want to bail if we made new allocations or have
> + * outstanding allocations in this block group. We do
> + * the ro check in case balance is currently acting on
> + * this block group.
> + */
> + spin_unlock(&bg->lock);
> + up_write(&space_info->groups_sem);
> + goto next;
> + }
> + spin_unlock(&bg->lock);
> +
> + ret = inc_block_group_ro(bg, 0);
> + up_write(&space_info->groups_sem);
> + if (ret < 0) {
> + ret = 0;
> + goto next;
> + }
> +
> + btrfs_info(fs_info, "reclaiming chunk %llu", bg->start);
> + trace_btrfs_reclaim_block_group(bg);
> + ret = btrfs_relocate_chunk(fs_info, bg->start);
I think you forgot to test this with lockdep enabled, it should have
complained loudly otherwise.
btrfs_relocate_chunk() calls lockdep_assert_head() to verify we are
holding fs_info->reclaim_bgs_lock,
but we just unlocked it.
Thanks.
> + if (ret)
> + btrfs_err(fs_info, "error relocating chunk %llu",
> + bg->start);
> +
> +next:
> + btrfs_put_block_group(bg);
> + mutex_lock(&fs_info->reclaim_bgs_lock);
> + }
> + mutex_unlock(&fs_info->reclaim_bgs_lock);
> + btrfs_exclop_finish(fs_info);
> +}
> +
> +void btrfs_mark_bg_to_reclaim(struct btrfs_block_group *bg)
> +{
> + struct btrfs_fs_info *fs_info = bg->fs_info;
> +
> + mutex_lock(&fs_info->reclaim_bgs_lock);
> + if (list_empty(&bg->bg_list)) {
> + btrfs_get_block_group(bg);
> + trace_btrfs_add_reclaim_block_group(bg);
> + list_add_tail(&bg->bg_list, &fs_info->reclaim_bgs);
> + }
> + mutex_unlock(&fs_info->reclaim_bgs_lock);
> +}
> +
> static int read_bg_from_eb(struct btrfs_fs_info *fs_info, struct btrfs_key
> *key,
> struct btrfs_path *path)
> {
> @@ -3390,6 +3464,16 @@ int btrfs_free_block_groups(struct btrfs_fs_info *info)
> }
> spin_unlock(&info->unused_bgs_lock);
>
> + mutex_lock(&info->reclaim_bgs_lock);
> + while (!list_empty(&info->reclaim_bgs)) {
> + block_group = list_first_entry(&info->reclaim_bgs,
> + struct btrfs_block_group,
> + bg_list);
> + list_del_init(&block_group->bg_list);
> + btrfs_put_block_group(block_group);
> + }
> + mutex_unlock(&info->reclaim_bgs_lock);
> +
> spin_lock(&info->block_group_cache_lock);
> while ((n = rb_last(&info->block_group_cache_tree)) != NULL) {
> block_group = rb_entry(n, struct btrfs_block_group,
> diff --git a/fs/btrfs/block-group.h b/fs/btrfs/block-group.h
> index 3ecc3372a5ce..e75c79676241 100644
> --- a/fs/btrfs/block-group.h
> +++ b/fs/btrfs/block-group.h
> @@ -264,6 +264,8 @@ int btrfs_remove_block_group(struct btrfs_trans_handle
> *trans,
> u64 group_start, struct extent_map *em);
> void btrfs_delete_unused_bgs(struct btrfs_fs_info *fs_info);
> void btrfs_mark_bg_unused(struct btrfs_block_group *bg);
> +void btrfs_reclaim_bgs(struct btrfs_fs_info *fs_info);
> +void btrfs_mark_bg_to_reclaim(struct btrfs_block_group *bg);
> int btrfs_read_block_groups(struct btrfs_fs_info *info);
> int btrfs_make_block_group(struct btrfs_trans_handle *trans, u64 bytes_used,
> u64 type, u64 chunk_offset, u64 size);
> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> index 34ec82d6df3e..0b438b97fed4 100644
> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> @@ -938,6 +938,7 @@ struct btrfs_fs_info {
> struct list_head unused_bgs;
> struct mutex unused_bg_unpin_mutex;
> struct mutex reclaim_bgs_lock;
> + struct list_head reclaim_bgs;
>
> /* Cached block sizes */
> u32 nodesize;
> @@ -978,6 +979,8 @@ struct btrfs_fs_info {
> spinlock_t treelog_bg_lock;
> u64 treelog_bg;
>
> + int bg_reclaim_threshold;
> +
> #ifdef CONFIG_BTRFS_FS_REF_VERIFY
> spinlock_t ref_verify_lock;
> struct rb_root block_tree;
> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> index f9250f14fc1e..d4fccf113df1 100644
> --- a/fs/btrfs/disk-io.c
> +++ b/fs/btrfs/disk-io.c
> @@ -1815,6 +1815,13 @@ static int cleaner_kthread(void *arg)
> * unused block groups.
> */
> btrfs_delete_unused_bgs(fs_info);
> +
> + /*
> + * Reclaim block groups in the reclaim_bgs list after we
> deleted
> + * all unused block_groups. This possibly gives us some more
> free
> + * space.
> + */
> + btrfs_reclaim_bgs(fs_info);
> sleep:
> clear_and_wake_up_bit(BTRFS_FS_CLEANER_RUNNING,
> &fs_info->flags);
> if (kthread_should_park())
> @@ -2797,12 +2804,14 @@ void btrfs_init_fs_info(struct btrfs_fs_info *fs_info)
> mutex_init(&fs_info->reloc_mutex);
> mutex_init(&fs_info->delalloc_root_mutex);
> mutex_init(&fs_info->zoned_meta_io_lock);
> + mutex_init(&fs_info->reclaim_bgs_lock);
> seqlock_init(&fs_info->profiles_lock);
>
> INIT_LIST_HEAD(&fs_info->dirty_cowonly_roots);
> INIT_LIST_HEAD(&fs_info->space_info);
> INIT_LIST_HEAD(&fs_info->tree_mod_seq_list);
> INIT_LIST_HEAD(&fs_info->unused_bgs);
> + INIT_LIST_HEAD(&fs_info->reclaim_bgs);
> #ifdef CONFIG_BTRFS_DEBUG
> INIT_LIST_HEAD(&fs_info->allocated_roots);
> INIT_LIST_HEAD(&fs_info->allocated_ebs);
> @@ -2891,6 +2900,8 @@ void btrfs_init_fs_info(struct btrfs_fs_info *fs_info)
> fs_info->swapfile_pins = RB_ROOT;
>
> fs_info->send_in_progress = 0;
> +
> + fs_info->bg_reclaim_threshold = 75;
> }
>
> static int init_mount_fs_info(struct btrfs_fs_info *fs_info, struct
> super_block *sb)
> diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
> index 9988decd5717..e54466fc101f 100644
> --- a/fs/btrfs/free-space-cache.c
> +++ b/fs/btrfs/free-space-cache.c
> @@ -11,6 +11,7 @@
> #include <linux/ratelimit.h>
> #include <linux/error-injection.h>
> #include <linux/sched/mm.h>
> +#include "misc.h"
> #include "ctree.h"
> #include "free-space-cache.h"
> #include "transaction.h"
> @@ -2539,6 +2540,7 @@ int __btrfs_add_free_space(struct btrfs_fs_info
> *fs_info,
> static int __btrfs_add_free_space_zoned(struct btrfs_block_group
> *block_group,
> u64 bytenr, u64 size, bool used)
> {
> + struct btrfs_fs_info *fs_info = block_group->fs_info;
> struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
> u64 offset = bytenr - block_group->start;
> u64 to_free, to_unusable;
> @@ -2569,8 +2571,13 @@ static int __btrfs_add_free_space_zoned(struct
> btrfs_block_group *block_group,
> }
>
> /* All the region is now unusable. Mark it as unused and reclaim */
> - if (block_group->zone_unusable == block_group->length)
> + if (block_group->zone_unusable == block_group->length) {
> btrfs_mark_bg_unused(block_group);
> + } else if (block_group->zone_unusable >=
> + div_factor_fine(block_group->length,
> + fs_info->bg_reclaim_threshold)) {
> + btrfs_mark_bg_to_reclaim(block_group);
> + }
>
> return 0;
> }
> diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
> index 6eb1c50fa98c..bf38c7c6b804 100644
> --- a/fs/btrfs/sysfs.c
> +++ b/fs/btrfs/sysfs.c
> @@ -965,6 +965,40 @@ static ssize_t btrfs_read_policy_store(struct kobject
> *kobj,
> }
> BTRFS_ATTR_RW(, read_policy, btrfs_read_policy_show,
> btrfs_read_policy_store);
>
> +static ssize_t btrfs_bg_reclaim_threshold_show(struct kobject *kobj,
> + struct kobj_attribute *a,
> + char *buf)
> +{
> + struct btrfs_fs_info *fs_info = to_fs_info(kobj);
> + ssize_t ret;
> +
> + ret = scnprintf(buf, PAGE_SIZE, "%d\n",
> fs_info->bg_reclaim_threshold);
> +
> + return ret;
> +}
> +
> +static ssize_t btrfs_bg_reclaim_threshold_store(struct kobject *kobj,
> + struct kobj_attribute *a,
> + const char *buf, size_t len)
> +{
> + struct btrfs_fs_info *fs_info = to_fs_info(kobj);
> + int thresh;
> + int ret;
> +
> + ret = kstrtoint(buf, 10, &thresh);
> + if (ret)
> + return ret;
> +
> + if (thresh <= 50 || thresh > 100)
> + return -EINVAL;
> +
> + fs_info->bg_reclaim_threshold = thresh;
> +
> + return len;
> +}
> +BTRFS_ATTR_RW(, bg_reclaim_threshold, btrfs_bg_reclaim_threshold_show,
> + btrfs_bg_reclaim_threshold_store);
> +
> static const struct attribute *btrfs_attrs[] = {
> BTRFS_ATTR_PTR(, label),
> BTRFS_ATTR_PTR(, nodesize),
> @@ -976,6 +1010,7 @@ static const struct attribute *btrfs_attrs[] = {
> BTRFS_ATTR_PTR(, exclusive_operation),
> BTRFS_ATTR_PTR(, generation),
> BTRFS_ATTR_PTR(, read_policy),
> + BTRFS_ATTR_PTR(, bg_reclaim_threshold),
> NULL,
> };
>
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index fb785ff53a27..c78b5ce49d47 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -3098,7 +3098,7 @@ int btrfs_remove_chunk(struct btrfs_trans_handle
> *trans, u64 chunk_offset)
> return ret;
> }
>
> -static int btrfs_relocate_chunk(struct btrfs_fs_info *fs_info, u64
> chunk_offset)
> +int btrfs_relocate_chunk(struct btrfs_fs_info *fs_info, u64 chunk_offset)
> {
> struct btrfs_root *root = fs_info->chunk_root;
> struct btrfs_trans_handle *trans;
> diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
> index d4c3e0dd32b8..9c0d84e5ec06 100644
> --- a/fs/btrfs/volumes.h
> +++ b/fs/btrfs/volumes.h
> @@ -484,6 +484,7 @@ void btrfs_describe_block_groups(u64 flags, char *buf,
> u32 size_buf);
> int btrfs_resume_balance_async(struct btrfs_fs_info *fs_info);
> int btrfs_recover_balance(struct btrfs_fs_info *fs_info);
> int btrfs_pause_balance(struct btrfs_fs_info *fs_info);
> +int btrfs_relocate_chunk(struct btrfs_fs_info *fs_info, u64 chunk_offset);
> int btrfs_cancel_balance(struct btrfs_fs_info *fs_info);
> int btrfs_create_uuid_tree(struct btrfs_fs_info *fs_info);
> int btrfs_uuid_scan_kthread(void *data);
> diff --git a/include/trace/events/btrfs.h b/include/trace/events/btrfs.h
> index 0551ea65374f..a41dd8a0c730 100644
> --- a/include/trace/events/btrfs.h
> +++ b/include/trace/events/btrfs.h
> @@ -1903,6 +1903,18 @@ DEFINE_EVENT(btrfs__block_group,
> btrfs_add_unused_block_group,
> TP_ARGS(bg_cache)
> );
>
> +DEFINE_EVENT(btrfs__block_group, btrfs_add_reclaim_block_group,
> + TP_PROTO(const struct btrfs_block_group *bg_cache),
> +
> + TP_ARGS(bg_cache)
> +);
> +
> +DEFINE_EVENT(btrfs__block_group, btrfs_reclaim_block_group,
> + TP_PROTO(const struct btrfs_block_group *bg_cache),
> +
> + TP_ARGS(bg_cache)
> +);
> +
> DEFINE_EVENT(btrfs__block_group, btrfs_skip_unused_block_group,
> TP_PROTO(const struct btrfs_block_group *bg_cache),
>
> --
> 2.30.0
>
--
Filipe David Manana,
“Whether you think you can, or you think you can't — you're right.”
