On Fri, Dec 13, 2019 at 04:22:24PM -0800, Dennis Zhou wrote:
> Throttle the maximum size of a discard so that we can provide an upper
> bound for the rate of async discard. While the block layer is able to
> split discards into the appropriate sized discards, we want to be able
> to account more accurately the rate at which we are consuming ncq slots
> as well as limit the upper bound of work for a discard.
>
> Signed-off-by: Dennis Zhou <dennis@xxxxxxxxxx>
> Reviewed-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
> ---
> fs/btrfs/discard.h | 5 ++++
> fs/btrfs/free-space-cache.c | 48 +++++++++++++++++++++++++++----------
> 2 files changed, 41 insertions(+), 12 deletions(-)
>
> diff --git a/fs/btrfs/discard.h b/fs/btrfs/discard.h
> index 3ed6855e24da..cb6ef0ab879d 100644
> --- a/fs/btrfs/discard.h
> +++ b/fs/btrfs/discard.h
> @@ -3,10 +3,15 @@
> #ifndef BTRFS_DISCARD_H
> #define BTRFS_DISCARD_H
>
> +#include <linux/sizes.h>
> +
> struct btrfs_fs_info;
> struct btrfs_discard_ctl;
> struct btrfs_block_group;
>
> +/* Discard size limits. */
> +#define BTRFS_ASYNC_DISCARD_MAX_SIZE (SZ_64M)
> +
> /* Work operations. */
> void btrfs_discard_cancel_work(struct btrfs_discard_ctl *discard_ctl,
> struct btrfs_block_group *block_group);
> diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
> index 57df34480b93..0dbcea6c59f9 100644
> --- a/fs/btrfs/free-space-cache.c
> +++ b/fs/btrfs/free-space-cache.c
> @@ -3466,19 +3466,40 @@ static int trim_no_bitmap(struct btrfs_block_group *block_group,
> if (entry->offset >= end)
> goto out_unlock;
>
> - extent_start = entry->offset;
> - extent_bytes = entry->bytes;
> - extent_trim_state = entry->trim_state;
> - start = max(start, extent_start);
> - bytes = min(extent_start + extent_bytes, end) - start;
> - if (bytes < minlen) {
> - spin_unlock(&ctl->tree_lock);
> - mutex_unlock(&ctl->cache_writeout_mutex);
> - goto next;
> - }
> + if (async) {
> + start = extent_start = entry->offset;
> + bytes = extent_bytes = entry->bytes;
Please avoid chain initializations, I'll fix that unless there are more
updates to this patch.
> + extent_trim_state = entry->trim_state;
> + if (bytes < minlen) {
> + spin_unlock(&ctl->tree_lock);
> + mutex_unlock(&ctl->cache_writeout_mutex);
> + goto next;
> + }
> + unlink_free_space(ctl, entry);
> + if (bytes > BTRFS_ASYNC_DISCARD_MAX_SIZE) {
> + bytes = extent_bytes =
> + BTRFS_ASYNC_DISCARD_MAX_SIZE;
> + entry->offset += BTRFS_ASYNC_DISCARD_MAX_SIZE;
> + entry->bytes -= BTRFS_ASYNC_DISCARD_MAX_SIZE;
> + link_free_space(ctl, entry);
> + } else {
> + kmem_cache_free(btrfs_free_space_cachep, entry);
> + }
> + } else {
> + extent_start = entry->offset;
> + extent_bytes = entry->bytes;
> + extent_trim_state = entry->trim_state;
> + start = max(start, extent_start);
> + bytes = min(extent_start + extent_bytes, end) - start;
> + if (bytes < minlen) {
> + spin_unlock(&ctl->tree_lock);
> + mutex_unlock(&ctl->cache_writeout_mutex);
> + goto next;
> + }
>
> - unlink_free_space(ctl, entry);
> - kmem_cache_free(btrfs_free_space_cachep, entry);
> + unlink_free_space(ctl, entry);
> + kmem_cache_free(btrfs_free_space_cachep, entry);
> + }
>
> spin_unlock(&ctl->tree_lock);
> trim_entry.start = extent_start;
> @@ -3643,6 +3664,9 @@ static int trim_bitmaps(struct btrfs_block_group *block_group,
> goto next;
> }
>
> + if (async && bytes > BTRFS_ASYNC_DISCARD_MAX_SIZE)
> + bytes = BTRFS_ASYNC_DISCARD_MAX_SIZE;
> +
> bitmap_clear_bits(ctl, entry, start, bytes);
> if (entry->bytes == 0)
> free_bitmap(ctl, entry);
> --
> 2.17.1
