In dm-snapshot target there may be large number of copy requests in
progress. If every pending copy request consumed a process context, it
would put too much load on the system.
To avoid this load, we need asynchronous notification when copy finishes -
we can pass a callback to the function blkdev_issue_copy, if the callback
is non-NULL, blkdev_issue_copy exits when it submits all the copy bios and
the callback is called when the copy operation finishes.
With the callback mechanism, there can be large number of in-progress copy
requests and we do not need process context for each of them.
Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
---
block/blk-lib.c | 148 +++++++++++++++++++++++++++++++++-------------
block/ioctl.c | 2
include/linux/blk_types.h | 5 -
include/linux/blkdev.h | 2
4 files changed, 112 insertions(+), 45 deletions(-)
Index: linux-4.4-rc4/block/blk-lib.c
===================================================================
--- linux-4.4-rc4.orig/block/blk-lib.c 2015-12-10 17:04:45.000000000 +0100
+++ linux-4.4-rc4/block/blk-lib.c 2015-12-10 17:04:46.000000000 +0100
@@ -300,6 +300,17 @@ int blkdev_issue_zeroout(struct block_de
}
EXPORT_SYMBOL(blkdev_issue_zeroout);
+struct bio_copy_batch {
+ atomic_long_t done;
+ int async_error;
+ int sync_error;
+ sector_t sync_copied;
+ atomic64_t first_error;
+ void (*callback)(void *data, int error);
+ void *data;
+ sector_t *copied;
+};
+
#define BLK_COPY_TIMEOUT (10 * HZ)
static void blk_copy_timeout(unsigned long bc_)
@@ -328,6 +339,18 @@ static void blk_copy_timeout(unsigned lo
}
}
+static void blk_copy_batch_finish(struct bio_copy_batch *batch)
+{
+ void (*fn)(void *, int) = batch->callback;
+ void *data = batch->data;
+ int error = unlikely(batch->sync_error) ? batch->sync_error : batch->async_error;
+ if (batch->copied)
+ *batch->copied = min(batch->sync_copied, (sector_t)atomic64_read(&batch->first_error));
+ kfree(batch);
+ if (fn)
+ fn(data, error);
+}
+
static void bio_copy_end_io(struct bio *bio)
{
struct bio_copy *bc = bio->bi_copy;
@@ -351,25 +374,37 @@ static void bio_copy_end_io(struct bio *
}
bio_put(bio);
if (atomic_dec_and_test(&bc->in_flight)) {
- struct bio_batch *bb = bc->private;
+ struct bio_copy_batch *batch = bc->batch;
if (unlikely(bc->error < 0)) {
u64 first_error;
- if (!ACCESS_ONCE(bb->error))
- ACCESS_ONCE(bb->error) = bc->error;
+ if (!ACCESS_ONCE(batch->async_error))
+ ACCESS_ONCE(batch->async_error) = bc->error;
do {
- first_error = atomic64_read(bc->first_error);
+ first_error = atomic64_read(&batch->first_error);
if (bc->offset >= first_error)
break;
- } while (unlikely(atomic64_cmpxchg(bc->first_error,
+ } while (unlikely(atomic64_cmpxchg(&batch->first_error,
first_error, bc->offset) != first_error));
}
del_timer_sync(&bc->timer);
kfree(bc);
- if (atomic_dec_and_test(&bb->done))
- complete(bb->wait);
+ if (atomic_long_dec_and_test(&batch->done))
+ blk_copy_batch_finish(batch);
}
}
+struct bio_copy_completion {
+ struct completion wait;
+ int error;
+};
+
+static void bio_copy_sync_callback(void *ptr, int error)
+{
+ struct bio_copy_completion *comp = ptr;
+ comp->error = error;
+ complete(&comp->wait);
+}
+
/**
* blkdev_issue_copy - queue a copy same operation
* @src_bdev: source blockdev
@@ -384,57 +419,83 @@ static void bio_copy_end_io(struct bio *
*/
int blkdev_issue_copy(struct block_device *src_bdev, sector_t src_sector,
struct block_device *dst_bdev, sector_t dst_sector,
- sector_t nr_sects, gfp_t gfp_mask, sector_t *copied)
+ sector_t nr_sects, gfp_t gfp_mask,
+ void (*callback)(void *, int), void *data,
+ sector_t *copied)
{
DECLARE_COMPLETION_ONSTACK(wait);
struct request_queue *sq = bdev_get_queue(src_bdev);
struct request_queue *dq = bdev_get_queue(dst_bdev);
unsigned int max_copy_sectors;
- struct bio_batch bb;
- int ret = 0;
- atomic64_t first_error = ATOMIC64_INIT(nr_sects);
- sector_t offset = 0;
+ int ret;
+ struct bio_copy_batch *batch;
+ struct bio_copy_completion comp;
if (copied)
*copied = 0;
- if (!sq || !dq)
- return -ENXIO;
+ if (!sq || !dq) {
+ ret = -ENXIO;
+ goto end_callback;
+ }
max_copy_sectors = min(sq->limits.max_copy_sectors,
dq->limits.max_copy_sectors);
- if (max_copy_sectors == 0)
- return -EOPNOTSUPP;
+ if (max_copy_sectors == 0) {
+ ret = -EOPNOTSUPP;
+ goto end_callback;
+ }
if (src_sector + nr_sects < src_sector ||
- dst_sector + nr_sects < dst_sector)
- return -EINVAL;
+ dst_sector + nr_sects < dst_sector) {
+ ret = -EINVAL;
+ goto end_callback;
+ }
/* Do not support overlapping copies */
if (src_bdev == dst_bdev &&
- abs((u64)dst_sector - (u64)src_sector) < nr_sects)
- return -EOPNOTSUPP;
+ abs((u64)dst_sector - (u64)src_sector) < nr_sects) {
+ ret = -EOPNOTSUPP;
+ goto end_callback;
+ }
- atomic_set(&bb.done, 1);
- bb.error = 0;
- bb.wait = &wait;
+ batch = kmalloc(sizeof(struct bio_copy_batch), gfp_mask);
+ if (!batch) {
+ ret = -ENOMEM;
+ goto end_callback;
+ }
+
+ batch->done = (atomic_long_t)ATOMIC_LONG_INIT(1);
+ batch->async_error = 0;
+ batch->sync_error = 0;
+ batch->sync_copied = 0;
+ batch->first_error = (atomic64_t)ATOMIC64_INIT(nr_sects);
+ batch->copied = copied;
+ if (callback) {
+ batch->callback = callback;
+ batch->data = data;
+ } else {
+ comp.wait = COMPLETION_INITIALIZER_ONSTACK(comp.wait);
+ batch->callback = bio_copy_sync_callback;
+ batch->data = ∁
+ }
- while (nr_sects && !ACCESS_ONCE(bb.error)) {
+ while (nr_sects && !ACCESS_ONCE(batch->async_error)) {
struct bio *read_bio, *write_bio;
struct bio_copy *bc;
unsigned chunk = (unsigned)min(nr_sects, (sector_t)max_copy_sectors);
bc = kmalloc(sizeof(struct bio_copy), gfp_mask);
if (!bc) {
- ret = -ENOMEM;
+ batch->sync_error = -ENOMEM;
break;
}
read_bio = bio_alloc(gfp_mask, 1);
if (!read_bio) {
kfree(bc);
- ret = -ENOMEM;
+ batch->sync_error = -ENOMEM;
break;
}
@@ -442,7 +503,7 @@ int blkdev_issue_copy(struct block_devic
if (!write_bio) {
bio_put(read_bio);
kfree(bc);
- ret = -ENOMEM;
+ batch->sync_error = -ENOMEM;
break;
}
@@ -450,9 +511,8 @@ int blkdev_issue_copy(struct block_devic
bc->error = 1;
bc->pair[0] = NULL;
bc->pair[1] = NULL;
- bc->private = &bb;
- bc->first_error = &first_error;
- bc->offset = offset;
+ bc->batch = batch;
+ bc->offset = batch->sync_copied;
spin_lock_init(&bc->spinlock);
__setup_timer(&bc->timer, blk_copy_timeout, (unsigned long)bc, TIMER_IRQSAFE);
mod_timer(&bc->timer, jiffies + BLK_COPY_TIMEOUT);
@@ -469,27 +529,33 @@ int blkdev_issue_copy(struct block_devic
write_bio->bi_bdev = dst_bdev;
write_bio->bi_copy = bc;
- atomic_inc(&bb.done);
+ atomic_long_inc(&batch->done);
submit_bio(READ | REQ_COPY, read_bio);
submit_bio(WRITE | REQ_COPY, write_bio);
src_sector += chunk;
dst_sector += chunk;
nr_sects -= chunk;
- offset += chunk;
+ batch->sync_copied += chunk;
}
- /* Wait for bios in-flight */
- if (!atomic_dec_and_test(&bb.done))
- wait_for_completion_io(&wait);
+ if (atomic_long_dec_and_test(&batch->done))
+ blk_copy_batch_finish(batch);
- if (copied)
- *copied = min((sector_t)atomic64_read(&first_error), offset);
-
- if (likely(!ret))
- ret = bb.error;
+ if (callback) {
+ return 0;
+ } else {
+ wait_for_completion_io(&comp.wait);
+ return comp.error;
+ }
- return ret;
+end_callback:
+ if (callback) {
+ callback(data, ret);
+ return 0;
+ } else {
+ return ret;
+ }
}
EXPORT_SYMBOL(blkdev_issue_copy);
Index: linux-4.4-rc4/include/linux/blk_types.h
===================================================================
--- linux-4.4-rc4.orig/include/linux/blk_types.h 2015-12-10 17:04:45.000000000 +0100
+++ linux-4.4-rc4/include/linux/blk_types.h 2015-12-10 17:04:46.000000000 +0100
@@ -40,6 +40,8 @@ struct bvec_iter {
current bvec */
};
+struct bio_copy_batch;
+
struct bio_copy {
/*
* error == 1 - bios are waiting to be paired
@@ -49,8 +51,7 @@ struct bio_copy {
int error;
atomic_t in_flight;
struct bio *pair[2];
- void *private;
- atomic64_t *first_error;
+ struct bio_copy_batch *batch;
sector_t offset;
spinlock_t spinlock;
struct timer_list timer;
Index: linux-4.4-rc4/include/linux/blkdev.h
===================================================================
--- linux-4.4-rc4.orig/include/linux/blkdev.h 2015-12-10 17:04:40.000000000 +0100
+++ linux-4.4-rc4/include/linux/blkdev.h 2015-12-10 17:04:46.000000000 +0100
@@ -1142,7 +1142,7 @@ extern int blkdev_issue_write_same(struc
sector_t nr_sects, gfp_t gfp_mask, struct page *page);
extern int blkdev_issue_copy(struct block_device *, sector_t,
struct block_device *, sector_t, sector_t, gfp_t,
- sector_t *);
+ void (*)(void *, int), void *, sector_t *);
extern int blkdev_issue_zeroout(struct block_device *bdev, sector_t sector,
sector_t nr_sects, gfp_t gfp_mask, bool discard);
static inline int sb_issue_discard(struct super_block *sb, sector_t block,
Index: linux-4.4-rc4/block/ioctl.c
===================================================================
--- linux-4.4-rc4.orig/block/ioctl.c 2015-12-10 17:04:40.000000000 +0100
+++ linux-4.4-rc4/block/ioctl.c 2015-12-10 17:04:46.000000000 +0100
@@ -276,7 +276,7 @@ static int blk_ioctl_copy(struct block_d
return -EINVAL;
ret = blkdev_issue_copy(bdev, src_offset, bdev, dst_offset, len,
- GFP_KERNEL, &copied_sec);
+ GFP_KERNEL, NULL, NULL, &copied_sec);
*copied = (uint64_t)copied_sec << 9;
--
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