[PATCH] btrfs: zoned: use greedy gc for auto reclaim

[PATCH] btrfs: zoned: use greedy gc for auto reclaim

[Johannes Thumshirn]

Currently auto reclaim of unusable zones reclaims the block-groups in the
order they have been added to the reclaim list.

Change this to a greedy algorithm by sorting the list so we have the
block-groups with the least amount of valid bytes reclaimed first.

Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>

---
Changes since RFC:
- Updated the patch description
- Don't sort the list under the spin_lock (David)
---
 fs/btrfs/block-group.c | 29 +++++++++++++++++++++++++----
 1 file changed, 25 insertions(+), 4 deletions(-)

diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
index 46fdef7bbe20..930c07cdad81 100644
--- a/fs/btrfs/block-group.c
+++ b/fs/btrfs/block-group.c
@@ -1,5 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 
+#include <linux/list_sort.h>
+
 #include "misc.h"
 #include "ctree.h"
 #include "block-group.h"
@@ -1486,6 +1488,21 @@ void btrfs_mark_bg_unused(struct btrfs_block_group *bg)
 	spin_unlock(&fs_info->unused_bgs_lock);
 }
 
+/*
+ * We want block groups with a low number of used bytes to be in the beginning
+ * of the list, so they will get reclaimed first.
+ */
+static int reclaim_bgs_cmp(void *unused, const struct list_head *a,
+			   const struct list_head *b)
+{
+	const struct btrfs_block_group *bg1, *bg2;
+
+	bg1 = list_entry(a, struct btrfs_block_group, bg_list);
+	bg2 = list_entry(b, struct btrfs_block_group, bg_list);
+
+	return bg1->used - bg2->used;
+}
+
 void btrfs_reclaim_bgs_work(struct work_struct *work)
 {
 	struct btrfs_fs_info *fs_info =
@@ -1493,6 +1510,7 @@ void btrfs_reclaim_bgs_work(struct work_struct *work)
 	struct btrfs_block_group *bg;
 	struct btrfs_space_info *space_info;
 	LIST_HEAD(again_list);
+	LIST_HEAD(reclaim_list);
 
 	if (!test_bit(BTRFS_FS_OPEN, &fs_info->flags))
 		return;
@@ -1510,17 +1528,20 @@ void btrfs_reclaim_bgs_work(struct work_struct *work)
 	}
 
 	spin_lock(&fs_info->unused_bgs_lock);
-	while (!list_empty(&fs_info->reclaim_bgs)) {
+	list_splice_init(&fs_info->reclaim_bgs, &reclaim_list);
+	spin_unlock(&fs_info->unused_bgs_lock);
+
+	list_sort(NULL, &reclaim_list, reclaim_bgs_cmp);
+	while (!list_empty(&reclaim_list)) {
 		u64 zone_unusable;
 		int ret = 0;
 
-		bg = list_first_entry(&fs_info->reclaim_bgs,
+		bg = list_first_entry(&reclaim_list,
 				      struct btrfs_block_group,
 				      bg_list);
 		list_del_init(&bg->bg_list);
 
 		space_info = bg->space_info;
-		spin_unlock(&fs_info->unused_bgs_lock);
 
 		/* Don't race with allocators so take the groups_sem */
 		down_write(&space_info->groups_sem);
@@ -1568,12 +1589,12 @@ void btrfs_reclaim_bgs_work(struct work_struct *work)
 				  bg->start);
 
 next:
-		spin_lock(&fs_info->unused_bgs_lock);
 		if (ret == -EAGAIN && list_empty(&bg->bg_list))
 			list_add_tail(&bg->bg_list, &again_list);
 		else
 			btrfs_put_block_group(bg);
 	}
+	spin_lock(&fs_info->unused_bgs_lock);
 	list_splice_tail(&again_list, &fs_info->reclaim_bgs);
 	spin_unlock(&fs_info->unused_bgs_lock);
 	mutex_unlock(&fs_info->reclaim_bgs_lock);
-- 
2.32.0

Re: [PATCH] btrfs: zoned: use greedy gc for auto reclaim

[David Sterba]

On Mon, Oct 11, 2021 at 08:11:32PM +0900, Johannes Thumshirn wrote:
> Currently auto reclaim of unusable zones reclaims the block-groups in the
> order they have been added to the reclaim list.
> 
> Change this to a greedy algorithm by sorting the list so we have the
> block-groups with the least amount of valid bytes reclaimed first.
> 
> Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
> 
> ---
> Changes since RFC:
> - Updated the patch description
> - Don't sort the list under the spin_lock (David)
> ---
>  fs/btrfs/block-group.c | 29 +++++++++++++++++++++++++----
>  1 file changed, 25 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
> index 46fdef7bbe20..930c07cdad81 100644
> --- a/fs/btrfs/block-group.c
> +++ b/fs/btrfs/block-group.c
> @@ -1,5 +1,7 @@
>  // SPDX-License-Identifier: GPL-2.0
>  
> +#include <linux/list_sort.h>
> +
>  #include "misc.h"
>  #include "ctree.h"
>  #include "block-group.h"
> @@ -1486,6 +1488,21 @@ void btrfs_mark_bg_unused(struct btrfs_block_group *bg)
>  	spin_unlock(&fs_info->unused_bgs_lock);
>  }
>  
> +/*
> + * We want block groups with a low number of used bytes to be in the beginning
> + * of the list, so they will get reclaimed first.
> + */
> +static int reclaim_bgs_cmp(void *unused, const struct list_head *a,
> +			   const struct list_head *b)
> +{
> +	const struct btrfs_block_group *bg1, *bg2;
> +
> +	bg1 = list_entry(a, struct btrfs_block_group, bg_list);
> +	bg2 = list_entry(b, struct btrfs_block_group, bg_list);
> +
> +	return bg1->used - bg2->used;

It returns int but compares two u64, this should be either a if chaing
comparing all the possibilities or properly cast to s64.

Re: [PATCH] btrfs: zoned: use greedy gc for auto reclaim

[Johannes Thumshirn]

On 11/10/2021 16:52, David Sterba wrote:
>> +static int reclaim_bgs_cmp(void *unused, const struct list_head *a,
>> +			   const struct list_head *b)
>> +{
>> +	const struct btrfs_block_group *bg1, *bg2;
>> +
>> +	bg1 = list_entry(a, struct btrfs_block_group, bg_list);
>> +	bg2 = list_entry(b, struct btrfs_block_group, bg_list);
>> +
>> +	return bg1->used - bg2->used;
> 
> It returns int but compares two u64, this should be either a if chaing
> comparing all the possibilities or properly cast to s64.
> 

Looking at the documentation of list_sort() this can also be used
as a boolean, I'll do that then.