Re: [PATCH 4/4] btrfs: cleanup device states define BTRFS_DEV_STATE_CAN_DISCARD

[Anand Jain <anand.jain@oracle.com>]

On 11/29/2017 05:39 PM, Nikolay Borisov wrote:
> 
> 
> On 29.11.2017 06:45, Anand Jain wrote:
>> Currently device state is being managed by each individual int
>> variable such as struct btrfs_device::can_discard. Instead of that
>> declare btrfs_device::dev_state BTRFS_DEV_STATE_CAN_DISCARD and use
>> the bit operations.
>>
>> Signed-off-by: Anand Jain <anand.jain@oracle.com>
>> ---
>>   fs/btrfs/extent-tree.c | 3 ++-
>>   fs/btrfs/volumes.c     | 6 +++---
>>   fs/btrfs/volumes.h     | 2 +-
>>   3 files changed, 6 insertions(+), 5 deletions(-)
>>
>> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
>> index f81d928754e1..ee79f7cdc543 100644
>> --- a/fs/btrfs/extent-tree.c
>> +++ b/fs/btrfs/extent-tree.c
>> @@ -2155,7 +2155,8 @@ int btrfs_discard_extent(struct btrfs_fs_info *fs_info, u64 bytenr,
>>   
>>   		for (i = 0; i < bbio->num_stripes; i++, stripe++) {
>>   			u64 bytes;
>> -			if (!stripe->dev->can_discard)
>> +			if (!test_bit(BTRFS_DEV_STATE_CAN_DISCARD,
>> +						&stripe->dev->dev_state))
>>   				continue;
> 
> Given that we only check for discard support here I can't help but think
> do we really need to duplicate the information. We already have struct
> block_device in struct btrfs_device, why don't we query for discard
> support directly the underlying device, rather than duplicating
> information?

  I agree. bdev_get_queue(bdev) and blk_queue_discard(q) are light weight
  too.
  So I shall withdraw this patch and sent the following patch to
  remove can_discard altogether.
    [PATCH] btrfs: drop btrfs_device::can_discard to query directly

Thanks, Anand


>>   
>>   			ret = btrfs_issue_discard(stripe->dev->bdev,
>> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
>> index 75839e07ce10..a9c6486f06f4 100644
>> --- a/fs/btrfs/volumes.c
>> +++ b/fs/btrfs/volumes.c
>> @@ -647,7 +647,7 @@ static int btrfs_open_one_device(struct btrfs_fs_devices *fs_devices,
>>   
>>   	q = bdev_get_queue(bdev);
>>   	if (blk_queue_discard(q))
>> -		device->can_discard = 1;
>> +		set_bit(BTRFS_DEV_STATE_CAN_DISCARD, &device->dev_state);
>>   	if (!blk_queue_nonrot(q))
>>   		fs_devices->rotating = 1;
>>   
>> @@ -2401,7 +2401,7 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path
>>   
>>   	q = bdev_get_queue(bdev);
>>   	if (blk_queue_discard(q))
>> -		device->can_discard = 1;
>> +		set_bit(BTRFS_DEV_STATE_CAN_DISCARD, &device->dev_state);
>>   	set_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state);
>>   	device->generation = trans->transid;
>>   	device->io_width = fs_info->sectorsize;
>> @@ -2601,7 +2601,7 @@ int btrfs_init_dev_replace_tgtdev(struct btrfs_fs_info *fs_info,
>>   
>>   	q = bdev_get_queue(bdev);
>>   	if (blk_queue_discard(q))
>> -		device->can_discard = 1;
>> +		set_bit(BTRFS_DEV_STATE_CAN_DISCARD, &device->dev_state);
>>   	mutex_lock(&fs_info->fs_devices->device_list_mutex);
>>   	set_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state);
>>   	device->generation = 0;
>> diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
>> index 2fbff6902c8d..85e4b2dcc071 100644
>> --- a/fs/btrfs/volumes.h
>> +++ b/fs/btrfs/volumes.h
>> @@ -50,6 +50,7 @@ struct btrfs_pending_bios {
>>   #define BTRFS_DEV_STATE_WRITEABLE	(1UL << 1)
>>   #define BTRFS_DEV_STATE_IN_FS_METADATA	(1UL << 2)
>>   #define BTRFS_DEV_STATE_MISSING		(1UL << 3)
>> +#define BTRFS_DEV_STATE_CAN_DISCARD	(1UL << 4)
>>   
>>   struct btrfs_device {
>>   	struct list_head dev_list;
>> @@ -74,7 +75,6 @@ struct btrfs_device {
>>   	fmode_t mode;
>>   
>>   	unsigned long dev_state;
>> -	int can_discard;
>>   	int is_tgtdev_for_dev_replace;
>>   	blk_status_t last_flush_error;
>>   	int flush_bio_sent;
>>