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block: use an xarray for disk->part_tbl
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Now that no fast path lookups in the partition table are left, there is
no point in micro-optimizing the data structure for it.  Just use a bog
standard xarray.

Signed-off-by: Christoph Hellwig <[email protected]>
Acked-by: Tejun Heo <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>
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Christoph Hellwig authored and axboe committed Jan 25, 2021
1 parent 0470dd9 commit a33df75
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Showing 5 changed files with 22 additions and 193 deletions.
2 changes: 1 addition & 1 deletion block/blk-settings.c
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Original file line number Diff line number Diff line change
Expand Up @@ -865,7 +865,7 @@ void blk_queue_set_zoned(struct gendisk *disk, enum blk_zoned_model model)
* we do nothing special as far as the block layer is concerned.
*/
if (!IS_ENABLED(CONFIG_BLK_DEV_ZONED) ||
disk_has_partitions(disk))
!xa_empty(&disk->part_tbl))
model = BLK_ZONED_NONE;
break;
case BLK_ZONED_NONE:
Expand Down
1 change: 0 additions & 1 deletion block/blk.h
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Original file line number Diff line number Diff line change
Expand Up @@ -345,7 +345,6 @@ int bdev_add_partition(struct block_device *bdev, int partno,
int bdev_del_partition(struct block_device *bdev, int partno);
int bdev_resize_partition(struct block_device *bdev, int partno,
sector_t start, sector_t length);
int disk_expand_part_tbl(struct gendisk *disk, int target);

int bio_add_hw_page(struct request_queue *q, struct bio *bio,
struct page *page, unsigned int len, unsigned int offset,
Expand Down
163 changes: 12 additions & 151 deletions block/genhd.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -161,15 +161,6 @@ static void part_in_flight_rw(struct block_device *part,
inflight[1] = 0;
}

static struct block_device *__disk_get_part(struct gendisk *disk, int partno)
{
struct disk_part_tbl *ptbl = rcu_dereference(disk->part_tbl);

if (unlikely(partno < 0 || partno >= ptbl->len))
return NULL;
return rcu_dereference(ptbl->part[partno]);
}

/**
* disk_part_iter_init - initialize partition iterator
* @piter: iterator to initialize
Expand Down Expand Up @@ -204,41 +195,26 @@ void disk_part_iter_init(struct disk_part_iter *piter, struct gendisk *disk,
*/
struct block_device *disk_part_iter_next(struct disk_part_iter *piter)
{
struct disk_part_tbl *ptbl;
struct block_device *part;
unsigned long idx;

/* put the last partition */
disk_part_iter_exit(piter);

/* get part_tbl */
rcu_read_lock();
ptbl = rcu_dereference(piter->disk->part_tbl);

/* iterate to the next partition */
for (; piter->idx != ptbl->len; piter->idx += 1) {
struct block_device *part;

part = rcu_dereference(ptbl->part[piter->idx]);
if (!part)
continue;
piter->part = bdgrab(part);
if (!piter->part)
continue;
xa_for_each_start(&piter->disk->part_tbl, idx, part, piter->idx) {
if (!bdev_nr_sectors(part) &&
!(piter->flags & DISK_PITER_INCL_EMPTY) &&
!(piter->flags & DISK_PITER_INCL_EMPTY_PART0 &&
piter->idx == 0)) {
bdput(piter->part);
piter->part = NULL;
piter->idx == 0))
continue;
}

piter->part = bdgrab(part);
if (!piter->part)
continue;
piter->idx += 1;
piter->idx = idx + 1;
break;
}

rcu_read_unlock();

return piter->part;
Expand All @@ -260,42 +236,6 @@ void disk_part_iter_exit(struct disk_part_iter *piter)
piter->part = NULL;
}

/**
* disk_has_partitions
* @disk: gendisk of interest
*
* Walk through the partition table and check if valid partition exists.
*
* CONTEXT:
* Don't care.
*
* RETURNS:
* True if the gendisk has at least one valid non-zero size partition.
* Otherwise false.
*/
bool disk_has_partitions(struct gendisk *disk)
{
struct disk_part_tbl *ptbl;
int i;
bool ret = false;

rcu_read_lock();
ptbl = rcu_dereference(disk->part_tbl);

/* Iterate partitions skipping the whole device at index 0 */
for (i = 1; i < ptbl->len; i++) {
if (rcu_dereference(ptbl->part[i])) {
ret = true;
break;
}
}

rcu_read_unlock();

return ret;
}
EXPORT_SYMBOL_GPL(disk_has_partitions);

/*
* Can be deleted altogether. Later.
*
Expand Down Expand Up @@ -858,7 +798,7 @@ struct block_device *bdget_disk(struct gendisk *disk, int partno)
struct block_device *bdev = NULL;

rcu_read_lock();
bdev = __disk_get_part(disk, partno);
bdev = xa_load(&disk->part_tbl, partno);
if (bdev && !bdgrab(bdev))
bdev = NULL;
rcu_read_unlock();
Expand Down Expand Up @@ -1248,83 +1188,6 @@ static const struct attribute_group *disk_attr_groups[] = {
NULL
};

/**
* disk_replace_part_tbl - replace disk->part_tbl in RCU-safe way
* @disk: disk to replace part_tbl for
* @new_ptbl: new part_tbl to install
*
* Replace disk->part_tbl with @new_ptbl in RCU-safe way. The
* original ptbl is freed using RCU callback.
*
* LOCKING:
* Matching bd_mutex locked or the caller is the only user of @disk.
*/
static void disk_replace_part_tbl(struct gendisk *disk,
struct disk_part_tbl *new_ptbl)
{
struct disk_part_tbl *old_ptbl =
rcu_dereference_protected(disk->part_tbl, 1);

rcu_assign_pointer(disk->part_tbl, new_ptbl);

if (old_ptbl) {
rcu_assign_pointer(old_ptbl->last_lookup, NULL);
kfree_rcu(old_ptbl, rcu_head);
}
}

/**
* disk_expand_part_tbl - expand disk->part_tbl
* @disk: disk to expand part_tbl for
* @partno: expand such that this partno can fit in
*
* Expand disk->part_tbl such that @partno can fit in. disk->part_tbl
* uses RCU to allow unlocked dereferencing for stats and other stuff.
*
* LOCKING:
* Matching bd_mutex locked or the caller is the only user of @disk.
* Might sleep.
*
* RETURNS:
* 0 on success, -errno on failure.
*/
int disk_expand_part_tbl(struct gendisk *disk, int partno)
{
struct disk_part_tbl *old_ptbl =
rcu_dereference_protected(disk->part_tbl, 1);
struct disk_part_tbl *new_ptbl;
int len = old_ptbl ? old_ptbl->len : 0;
int i, target;

/*
* check for int overflow, since we can get here from blkpg_ioctl()
* with a user passed 'partno'.
*/
target = partno + 1;
if (target < 0)
return -EINVAL;

/* disk_max_parts() is zero during initialization, ignore if so */
if (disk_max_parts(disk) && target > disk_max_parts(disk))
return -EINVAL;

if (target <= len)
return 0;

new_ptbl = kzalloc_node(struct_size(new_ptbl, part, target), GFP_KERNEL,
disk->node_id);
if (!new_ptbl)
return -ENOMEM;

new_ptbl->len = target;

for (i = 0; i < len; i++)
rcu_assign_pointer(new_ptbl->part[i], old_ptbl->part[i]);

disk_replace_part_tbl(disk, new_ptbl);
return 0;
}

/**
* disk_release - releases all allocated resources of the gendisk
* @dev: the device representing this disk
Expand All @@ -1348,7 +1211,7 @@ static void disk_release(struct device *dev)
blk_free_devt(dev->devt);
disk_release_events(disk);
kfree(disk->random);
disk_replace_part_tbl(disk, NULL);
xa_destroy(&disk->part_tbl);
bdput(disk->part0);
if (disk->queue)
blk_put_queue(disk->queue);
Expand Down Expand Up @@ -1501,7 +1364,6 @@ dev_t blk_lookup_devt(const char *name, int partno)
struct gendisk *__alloc_disk_node(int minors, int node_id)
{
struct gendisk *disk;
struct disk_part_tbl *ptbl;

if (minors > DISK_MAX_PARTS) {
printk(KERN_ERR
Expand All @@ -1519,11 +1381,9 @@ struct gendisk *__alloc_disk_node(int minors, int node_id)
goto out_free_disk;

disk->node_id = node_id;
if (disk_expand_part_tbl(disk, 0))
goto out_bdput;

ptbl = rcu_dereference_protected(disk->part_tbl, 1);
rcu_assign_pointer(ptbl->part[0], disk->part0);
xa_init(&disk->part_tbl);
if (xa_insert(&disk->part_tbl, 0, disk->part0, GFP_KERNEL))
goto out_destroy_part_tbl;

disk->minors = minors;
rand_initialize_disk(disk);
Expand All @@ -1532,7 +1392,8 @@ struct gendisk *__alloc_disk_node(int minors, int node_id)
device_initialize(disk_to_dev(disk));
return disk;

out_bdput:
out_destroy_part_tbl:
xa_destroy(&disk->part_tbl);
bdput(disk->part0);
out_free_disk:
kfree(disk);
Expand Down
31 changes: 6 additions & 25 deletions block/partitions/core.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -287,13 +287,7 @@ struct device_type part_type = {
*/
void delete_partition(struct block_device *part)
{
struct gendisk *disk = part->bd_disk;
struct disk_part_tbl *ptbl =
rcu_dereference_protected(disk->part_tbl, 1);

rcu_assign_pointer(ptbl->part[part->bd_partno], NULL);
rcu_assign_pointer(ptbl->last_lookup, NULL);

xa_erase(&part->bd_disk->part_tbl, part->bd_partno);
kobject_put(part->bd_holder_dir);
device_del(&part->bd_device);

Expand Down Expand Up @@ -325,7 +319,6 @@ static struct block_device *add_partition(struct gendisk *disk, int partno,
struct device *ddev = disk_to_dev(disk);
struct device *pdev;
struct block_device *bdev;
struct disk_part_tbl *ptbl;
const char *dname;
int err;

Expand All @@ -347,12 +340,7 @@ static struct block_device *add_partition(struct gendisk *disk, int partno,
break;
}

err = disk_expand_part_tbl(disk, partno);
if (err)
return ERR_PTR(err);
ptbl = rcu_dereference_protected(disk->part_tbl, 1);

if (ptbl->part[partno])
if (xa_load(&disk->part_tbl, partno))
return ERR_PTR(-EBUSY);

bdev = bdev_alloc(disk, partno);
Expand Down Expand Up @@ -405,8 +393,10 @@ static struct block_device *add_partition(struct gendisk *disk, int partno,
}

/* everything is up and running, commence */
err = xa_insert(&disk->part_tbl, partno, bdev, GFP_KERNEL);
if (err)
goto out_del;
bdev_add(bdev, devt);
rcu_assign_pointer(ptbl->part[partno], bdev);

/* suppress uevent if the disk suppresses it */
if (!dev_get_uevent_suppress(ddev))
Expand Down Expand Up @@ -612,7 +602,7 @@ static bool blk_add_partition(struct gendisk *disk, struct block_device *bdev,
int blk_add_partitions(struct gendisk *disk, struct block_device *bdev)
{
struct parsed_partitions *state;
int ret = -EAGAIN, p, highest;
int ret = -EAGAIN, p;

if (!disk_part_scan_enabled(disk))
return 0;
Expand Down Expand Up @@ -660,15 +650,6 @@ int blk_add_partitions(struct gendisk *disk, struct block_device *bdev)
/* tell userspace that the media / partition table may have changed */
kobject_uevent(&disk_to_dev(disk)->kobj, KOBJ_CHANGE);

/*
* Detect the highest partition number and preallocate disk->part_tbl.
* This is an optimization and not strictly necessary.
*/
for (p = 1, highest = 0; p < state->limit; p++)
if (state->parts[p].size)
highest = p;
disk_expand_part_tbl(disk, highest);

for (p = 1; p < state->limit; p++)
if (!blk_add_partition(disk, bdev, state, p))
goto out_free_state;
Expand Down
18 changes: 3 additions & 15 deletions include/linux/genhd.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -32,6 +32,7 @@ extern struct class block_class;
#include <linux/string.h>
#include <linux/fs.h>
#include <linux/workqueue.h>
#include <linux/xarray.h>

#define PARTITION_META_INFO_VOLNAMELTH 64
/*
Expand Down Expand Up @@ -116,13 +117,6 @@ enum {
DISK_EVENT_FLAG_UEVENT = 1 << 1,
};

struct disk_part_tbl {
struct rcu_head rcu_head;
int len;
struct block_device __rcu *last_lookup;
struct block_device __rcu *part[];
};

struct disk_events;
struct badblocks;

Expand All @@ -148,12 +142,7 @@ struct gendisk {
unsigned short events; /* supported events */
unsigned short event_flags; /* flags related to event processing */

/* Array of pointers to partitions indexed by partno.
* Protected with matching bdev lock but stat and other
* non-critical accesses use RCU. Always access through
* helpers.
*/
struct disk_part_tbl __rcu *part_tbl;
struct xarray part_tbl;
struct block_device *part0;

const struct block_device_operations *fops;
Expand Down Expand Up @@ -225,15 +214,14 @@ void disk_uevent(struct gendisk *disk, enum kobject_action action);
struct disk_part_iter {
struct gendisk *disk;
struct block_device *part;
int idx;
unsigned long idx;
unsigned int flags;
};

extern void disk_part_iter_init(struct disk_part_iter *piter,
struct gendisk *disk, unsigned int flags);
struct block_device *disk_part_iter_next(struct disk_part_iter *piter);
extern void disk_part_iter_exit(struct disk_part_iter *piter);
extern bool disk_has_partitions(struct gendisk *disk);

/* block/genhd.c */
extern void device_add_disk(struct device *parent, struct gendisk *disk,
Expand Down

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