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Date: Mon, 20 Nov 2023 15:14:46 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: Ming Lei <ming.lei@...hat.com>, Yu Kuai <yukuai1@...weicloud.com>
Cc: axboe@...nel.dk, linux-block@...r.kernel.org,
linux-kernel@...r.kernel.org, yi.zhang@...wei.com,
yangerkun@...wei.com, "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH 1/2] block: introduce new field flags in block_device
Hi,
在 2023/11/20 14:58, Ming Lei 写道:
> On Mon, Nov 20, 2023 at 02:37:59PM +0800, Yu Kuai wrote:
>> Hi,
>>
>> 在 2023/11/20 11:00, Ming Lei 写道:
>>> On Mon, Nov 20, 2023 at 05:38:46PM +0800, Yu Kuai wrote:
>>>> From: Yu Kuai <yukuai3@...wei.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@...wei.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(¤t->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;
>
> 'bd_partno' needs to be kept in the 1st cacheline, so not good to move
> it.
>
Got it, and same for bd_dev and bd_openers, I'll send a new version
based on your first adivce.
Thanks,
Kuai
>
> Thanks,
> Ming
>
>
> .
>
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