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Subject: Re: [PATCH 1/2] block: introduce new field flags in block_device
To:     Ming Lei <ming.lei@redhat.com>, Yu Kuai <yukuai1@huaweicloud.com>
Cc:     axboe@kernel.dk, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org, yi.zhang@huawei.com,
        yangerkun@huawei.com, "yukuai (C)" <yukuai3@huawei.com>
References: <20231120093847.2228127-1-yukuai1@huaweicloud.com>
 <20231120093847.2228127-2-yukuai1@huaweicloud.com> <ZVrLvcIhlnQl7xAb@fedora>
From:   Yu Kuai <yukuai1@huaweicloud.com>
Message-ID: <9fc5e82f-9106-e3f9-4f06-d2d79e8e99a8@huaweicloud.com>
Date:   Mon, 20 Nov 2023 14:37:59 +0800
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Hi,

?? 2023/11/20 11:00, Ming Lei д??:
> On Mon, Nov 20, 2023 at 05:38:46PM +0800, Yu Kuai wrote:
>> From: Yu Kuai <yukuai3@huawei.com>
>>
>> There are multiple switches in struct block_device, use seperate bool
>> fields for them is not gracefully. Add a new field flags and replace
>> swithes to a bit, there are no functional changes, and preapre to add
>> a new switch in the next patch.
>>
>> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
>> ---
>>   block/bdev.c              | 15 ++++++++-------
>>   block/blk-core.c          |  7 ++++---
>>   block/genhd.c             |  8 +++++---
>>   block/ioctl.c             |  2 +-
>>   include/linux/blk_types.h | 12 ++++++------
>>   include/linux/blkdev.h    |  5 +++--
>>   6 files changed, 27 insertions(+), 22 deletions(-)
>>
>> diff --git a/block/bdev.c b/block/bdev.c
>> index fc8d28d77495..cb849bcf61ae 100644
>> --- a/block/bdev.c
>> +++ b/block/bdev.c
>> @@ -408,10 +408,10 @@ struct block_device *bdev_alloc(struct gendisk *disk, u8 partno)
>>   	bdev->bd_partno = partno;
>>   	bdev->bd_inode = inode;
>>   	bdev->bd_queue = disk->queue;
>> -	if (partno)
>> -		bdev->bd_has_submit_bio = disk->part0->bd_has_submit_bio;
>> +	if (partno && test_bit(BD_FLAG_HAS_SUBMIT_BIO, &disk->part0->flags))
>> +		set_bit(BD_FLAG_HAS_SUBMIT_BIO, &bdev->flags);
>>   	else
>> -		bdev->bd_has_submit_bio = false;
>> +		clear_bit(BD_FLAG_HAS_SUBMIT_BIO, &bdev->flags);
>>   	bdev->bd_stats = alloc_percpu(struct disk_stats);
>>   	if (!bdev->bd_stats) {
>>   		iput(inode);
>> @@ -612,7 +612,7 @@ static void bd_end_claim(struct block_device *bdev, void *holder)
>>   		bdev->bd_holder = NULL;
>>   		bdev->bd_holder_ops = NULL;
>>   		mutex_unlock(&bdev->bd_holder_lock);
>> -		if (bdev->bd_write_holder)
>> +		if (test_bit(BD_FLAG_WRITE_HOLDER, &bdev->flags))
>>   			unblock = true;
>>   	}
>>   	if (!whole->bd_holders)
>> @@ -625,7 +625,7 @@ static void bd_end_claim(struct block_device *bdev, void *holder)
>>   	 */
>>   	if (unblock) {
>>   		disk_unblock_events(bdev->bd_disk);
>> -		bdev->bd_write_holder = false;
>> +		clear_bit(BD_FLAG_WRITE_HOLDER, &bdev->flags);
>>   	}
>>   }
>>   
>> @@ -878,9 +878,10 @@ struct bdev_handle *bdev_open_by_dev(dev_t dev, blk_mode_t mode, void *holder,
>>   		 * writeable reference is too fragile given the way @mode is
>>   		 * used in blkdev_get/put().
>>   		 */
>> -		if ((mode & BLK_OPEN_WRITE) && !bdev->bd_write_holder &&
>> +		if ((mode & BLK_OPEN_WRITE) &&
>> +		    !test_bit(BD_FLAG_WRITE_HOLDER, &bdev->flags) &&
>>   		    (disk->event_flags & DISK_EVENT_FLAG_BLOCK_ON_EXCL_WRITE)) {
>> -			bdev->bd_write_holder = true;
>> +			set_bit(BD_FLAG_WRITE_HOLDER, &bdev->flags);
>>   			unblock_events = false;
>>   		}
>>   	}
>> diff --git a/block/blk-core.c b/block/blk-core.c
>> index fdf25b8d6e78..577a693165d8 100644
>> --- a/block/blk-core.c
>> +++ b/block/blk-core.c
>> @@ -482,7 +482,8 @@ __setup("fail_make_request=", setup_fail_make_request);
>>   
>>   bool should_fail_request(struct block_device *part, unsigned int bytes)
>>   {
>> -	return part->bd_make_it_fail && should_fail(&fail_make_request, bytes);
>> +	return test_bit(BD_FLAG_MAKE_IT_FAIL, &part->flags) &&
>> +		should_fail(&fail_make_request, bytes);
>>   }
>>   
>>   static int __init fail_make_request_debugfs(void)
>> @@ -595,7 +596,7 @@ static void __submit_bio(struct bio *bio)
>>   	if (unlikely(!blk_crypto_bio_prep(&bio)))
>>   		return;
>>   
>> -	if (!bio->bi_bdev->bd_has_submit_bio) {
>> +	if (!test_bit(BD_FLAG_HAS_SUBMIT_BIO, &bio->bi_bdev->flags)) {
>>   		blk_mq_submit_bio(bio);
>>   	} else if (likely(bio_queue_enter(bio) == 0)) {
>>   		struct gendisk *disk = bio->bi_bdev->bd_disk;
>> @@ -703,7 +704,7 @@ void submit_bio_noacct_nocheck(struct bio *bio)
>>   	 */
>>   	if (current->bio_list)
>>   		bio_list_add(&current->bio_list[0], bio);
>> -	else if (!bio->bi_bdev->bd_has_submit_bio)
>> +	else if (!test_bit(BD_FLAG_HAS_SUBMIT_BIO, &bio->bi_bdev->flags))
>>   		__submit_bio_noacct_mq(bio);
>>   	else
>>   		__submit_bio_noacct(bio);
>> diff --git a/block/genhd.c b/block/genhd.c
>> index c9d06f72c587..026f4c6d5b7e 100644
>> --- a/block/genhd.c
>> +++ b/block/genhd.c
>> @@ -413,7 +413,8 @@ int __must_check device_add_disk(struct device *parent, struct gendisk *disk,
>>   	elevator_init_mq(disk->queue);
>>   
>>   	/* Mark bdev as having a submit_bio, if needed */
>> -	disk->part0->bd_has_submit_bio = disk->fops->submit_bio != NULL;
>> +	if (disk->fops->submit_bio)
>> +		set_bit(BD_FLAG_HAS_SUBMIT_BIO, &disk->part0->flags);
>>   
>>   	/*
>>   	 * If the driver provides an explicit major number it also must provide
>> @@ -1062,7 +1063,8 @@ static DEVICE_ATTR(diskseq, 0444, diskseq_show, NULL);
>>   ssize_t part_fail_show(struct device *dev,
>>   		       struct device_attribute *attr, char *buf)
>>   {
>> -	return sprintf(buf, "%d\n", dev_to_bdev(dev)->bd_make_it_fail);
>> +	return sprintf(buf, "%d\n",
>> +		       test_bit(BD_FLAG_MAKE_IT_FAIL, &dev_to_bdev(dev)->flags));
>>   }
>>   
>>   ssize_t part_fail_store(struct device *dev,
>> @@ -1072,7 +1074,7 @@ ssize_t part_fail_store(struct device *dev,
>>   	int i;
>>   
>>   	if (count > 0 && sscanf(buf, "%d", &i) > 0)
>> -		dev_to_bdev(dev)->bd_make_it_fail = i;
>> +		set_bit(BD_FLAG_MAKE_IT_FAIL, &dev_to_bdev(dev)->flags);
>>   
>>   	return count;
>>   }
>> diff --git a/block/ioctl.c b/block/ioctl.c
>> index 4160f4e6bd5b..a548c718a5fb 100644
>> --- a/block/ioctl.c
>> +++ b/block/ioctl.c
>> @@ -394,7 +394,7 @@ static int blkdev_roset(struct block_device *bdev, unsigned cmd,
>>   		if (ret)
>>   			return ret;
>>   	}
>> -	bdev->bd_read_only = n;
>> +	set_bit(BD_FLAG_READ_ONLY, &bdev->flags);
>>   	return 0;
>>   }
>>   
>> diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
>> index 52e264d5a830..95bd26c62655 100644
>> --- a/include/linux/blk_types.h
>> +++ b/include/linux/blk_types.h
>> @@ -37,17 +37,20 @@ struct bio_crypt_ctx;
>>   #define PAGE_SECTORS		(1 << PAGE_SECTORS_SHIFT)
>>   #define SECTOR_MASK		(PAGE_SECTORS - 1)
>>   
>> +#define BD_FLAG_READ_ONLY	0 /* read-only-policy */
>> +#define BD_FLAG_WRITE_HOLDER	1
>> +#define BD_FLAG_HAS_SUBMIT_BIO	2
>> +#define BD_FLAG_MAKE_IT_FAIL	3
>> +
>>   struct block_device {
>>   	sector_t		bd_start_sect;
>>   	sector_t		bd_nr_sectors;
>>   	struct gendisk *	bd_disk;
>>   	struct request_queue *	bd_queue;
>>   	struct disk_stats __percpu *bd_stats;
>> +	unsigned long		flags;
>>   	unsigned long		bd_stamp;
>> -	bool			bd_read_only;	/* read-only policy */
>>   	u8			bd_partno;
>> -	bool			bd_write_holder;
>> -	bool			bd_has_submit_bio;
> 
> The idea looks good, but not necessary to add new 8 bytes, and you may
> put all these flags and `bd_partno` into single 'unsigned long', and add
> helpers to retrieve part no, since there are not many ->bd_partno
> references.

Yes, it make sense.

By the way, take a look at component of block_device, I think they can
be reorganized to save some space, in this case, new 8 bytes won't make
this struct bigger, in fact, total size will be shrinked by 8 types
after following changes:

diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index 95bd26c62655..c94242a9ad92 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -50,7 +50,6 @@ struct block_device {
         struct disk_stats __percpu *bd_stats;
         unsigned long           flags;
         unsigned long           bd_stamp;
-       u8                      bd_partno;
         dev_t                   bd_dev;
         atomic_t                bd_openers;
         spinlock_t              bd_size_lock; /* for bd_inode->i_size 
updates */
@@ -60,13 +59,14 @@ struct block_device {
         const struct blk_holder_ops *bd_holder_ops;
         struct mutex            bd_holder_lock;
         int                     bd_holders;
+       u8                      bd_partno;
         struct kobject          *bd_holder_dir;

-       atomic_t                bd_fsfreeze_count; /* number of freeze 
requests */
         struct mutex            bd_fsfreeze_mutex; /* serialize 
freeze/thaw */
+       atomic_t                bd_fsfreeze_count; /* number of freeze 
requests */

-       struct partition_meta_info *bd_meta_info;
         int                     bd_writers;
+       struct partition_meta_info *bd_meta_info;
         /*
          * keep this out-of-line as it's both big and not needed in the 
fast
          * path


Please let me know what you think.

Thanks,
Kuai

> 
> Thanks,
> Ming
> 
> 
> .
>