Re: [PATCH 1/2] block: introduce new field flags in block_device

From: Yu Kuai
Date: Mon Nov 20 2023 - 03:01:17 EST

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@xxxxxxxxxx>

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@xxxxxxxxxx>
---
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.

Hi, I'm not quite sure which is the best way to implement this, anyway,
I come up with following implementation, can you please take a look
before I send a new version?

diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index 52e264d5a830..4e29774b14fd 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -37,6 +37,12 @@ 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
+#define BD_FLAGS_MAX 16
+
struct block_device {
sector_t bd_start_sect;
sector_t bd_nr_sectors;
@@ -44,10 +50,20 @@ struct block_device {
struct request_queue * bd_queue;
struct disk_stats __percpu *bd_stats;
unsigned long bd_stamp;
- bool bd_read_only; /* read-only policy */
- u8 bd_partno;
- bool bd_write_holder;
- bool bd_has_submit_bio;
+
+ /*
+ * In order to keep both flags and bd_partno in the first cacheline,
+ * first 16 bits are used for flags.
+ */
+ union {
+ unsigned long flags;
+ struct {
+#ifdef __LITTLE_ENDIAN
+ u16 __flags;
+#endif
+ u8 bd_partno;
+ };
+ };

Thanks,
Kuai


Thanks,
Ming


.