Re: [PATCH v3] btrfs: zoned: make auto-reclaim less aggressive

[Josef Bacik <josef@toxicpanda.com>]

On Tue, Mar 15, 2022 at 04:02:57AM -0700, Johannes Thumshirn wrote:
> The current auto-reclaim algorithm starts reclaiming all block-group's
> with a zone_unusable value above a configured threshold. This is causing a
> lot of reclaim IO even if there would be enough free zones on the device.
> 
> Instead of only accounting a block-group's zone_unusable value, also take
> the number of empty zones into account.
> 
> Cc: Josef Bacik <josef@toxicpanda.com>
> Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
> 
> ---
> Changes since v4:
> * Use div_u64()
> 
> Changes since RFC:
> * Fix logic error
> * Skip unavailable devices
> * Use different metric working for non-zoned devices as well
> ---
>  fs/btrfs/block-group.c |  3 +++
>  fs/btrfs/zoned.c       | 30 ++++++++++++++++++++++++++++++
>  fs/btrfs/zoned.h       |  6 ++++++
>  3 files changed, 39 insertions(+)
> 
> diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
> index c22d287e020b..2e77b38c538b 100644
> --- a/fs/btrfs/block-group.c
> +++ b/fs/btrfs/block-group.c
> @@ -1522,6 +1522,9 @@ void btrfs_reclaim_bgs_work(struct work_struct *work)
>  	if (!test_bit(BTRFS_FS_OPEN, &fs_info->flags))
>  		return;
>  
> +	if (!btrfs_zoned_should_reclaim(fs_info))
> +		return;
> +

Noooo I just purposefully turned it on for everybody.

>  	sb_start_write(fs_info->sb);
>  
>  	if (!btrfs_exclop_start(fs_info, BTRFS_EXCLOP_BALANCE)) {
> diff --git a/fs/btrfs/zoned.c b/fs/btrfs/zoned.c
> index 49446bb5a5d1..dc62a14594de 100644
> --- a/fs/btrfs/zoned.c
> +++ b/fs/btrfs/zoned.c
> @@ -15,6 +15,7 @@
>  #include "transaction.h"
>  #include "dev-replace.h"
>  #include "space-info.h"
> +#include "misc.h"
>  
>  /* Maximum number of zones to report per blkdev_report_zones() call */
>  #define BTRFS_REPORT_NR_ZONES   4096
> @@ -2078,3 +2079,32 @@ void btrfs_free_zone_cache(struct btrfs_fs_info *fs_info)
>  	}
>  	mutex_unlock(&fs_devices->device_list_mutex);
>  }
> +
> +bool btrfs_zoned_should_reclaim(struct btrfs_fs_info *fs_info)
> +{
> +	struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
> +	struct btrfs_device *device;
> +	u64 bytes_used = 0;
> +	u64 total_bytes = 0;
> +	u64 factor;
> +
> +	if (!btrfs_is_zoned(fs_info))
> +		return false;
> +
> +	if (!fs_info->bg_reclaim_threshold)
> +		return false;
> +
> +	mutex_lock(&fs_devices->device_list_mutex);
> +	list_for_each_entry(device, &fs_devices->devices, dev_list) {
> +		if (!device->bdev)
> +			continue;
> +
> +		total_bytes += device->disk_total_bytes;
> +		bytes_used += device->bytes_used;
> +
> +	}
> +	mutex_unlock(&fs_devices->device_list_mutex);

We can probably export calc_available_free_space() and use that here instead,
I'd rather not be grabbing the device_list_mutex here if we can avoid it.

> +
> +	factor = div_u64(bytes_used * 100, total_bytes);
> +	return factor >= fs_info->bg_reclaim_threshold;

My patches removed the fs_info->bg_reclaim_threshold btw.  Thanks,

Josef