[03/12] btrfs: limit max discard size for async discard
diff mbox series

Message ID b0dada84ff74a4c7246acad7fe78250550b89f7f.1577999991.git.dennis@kernel.org
State New
Headers show
Series
  • btrfs: async discard follow up
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Commit Message

Dennis Zhou Jan. 2, 2020, 9:26 p.m. UTC
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@kernel.org>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
---
 fs/btrfs/discard.h          |  5 +++++
 fs/btrfs/free-space-cache.c | 41 +++++++++++++++++++++++++++++--------
 2 files changed, 37 insertions(+), 9 deletions(-)

Comments

David Sterba Jan. 3, 2020, 2:41 p.m. UTC | #1
On Thu, Jan 02, 2020 at 04:26:37PM -0500, 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@kernel.org>
> Reviewed-by: Josef Bacik <josef@toxicpanda.com>
> ---
>  fs/btrfs/discard.h          |  5 +++++
>  fs/btrfs/free-space-cache.c | 41 +++++++++++++++++++++++++++++--------
>  2 files changed, 37 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/btrfs/discard.h b/fs/btrfs/discard.h
> index 5250fe178e49..562c60fab77a 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 40fb918a82f4..34291c777998 100644
> --- a/fs/btrfs/free-space-cache.c
> +++ b/fs/btrfs/free-space-cache.c
> @@ -3466,16 +3466,36 @@ static int trim_no_bitmap(struct btrfs_block_group *block_group,
>  		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 = entry->offset;
> +			bytes = entry->bytes;
> +			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;

You still left one chain assignment here, fixed and also in the followup
patch that switches to the variable limit.

Patch
diff mbox series

diff --git a/fs/btrfs/discard.h b/fs/btrfs/discard.h
index 5250fe178e49..562c60fab77a 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 40fb918a82f4..34291c777998 100644
--- a/fs/btrfs/free-space-cache.c
+++ b/fs/btrfs/free-space-cache.c
@@ -3466,16 +3466,36 @@  static int trim_no_bitmap(struct btrfs_block_group *block_group,
 		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 = entry->offset;
+			bytes = entry->bytes;
+			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 {
+			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;
@@ -3639,6 +3659,9 @@  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);