Re: [RFC] [PATCH] A clean approach to writeout throttling

Daniel Phillips
2007-12-10T11:33:33Z

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On Monday 10 December 2007 02:47, Jens Axboe wrote:
> ...the warning on request_queue_t...

There you go, Jens, service with a smile.

Regards,

Daniel

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--- 2.6.24-rc3-mm.clean/block/ll_rw_blk.c 2007-12-04 14:45:25.000000000 -0800
+++ 2.6.24-rc3-mm/block/ll_rw_blk.c 2007-12-10 03:27:42.000000000 -0800
@@ -3210,7 +3210,7 @@ static inline int bio_check_eod(struct b
*/
static inline void __generic_make_request(struct bio *bio)
{
- struct request_queue *q;
+ struct request_queue *q = bdev_get_queue(bio->bi_bdev);
sector_t old_sector;
int ret, nr_sectors = bio_sectors(bio);
dev_t old_dev;
@@ -3221,6 +3221,13 @@ static inline void __generic_make_reques
if (bio_check_eod(bio, nr_sectors))
goto end_io;

+ if (q && q->metric && !bio->bi_queue) {
+ int need = bio->bi_throttle = q->metric(bio);
+ bio->bi_queue = q;
+ /* FIXME: potential race if atomic_sub is called in the middle of condition check */
+ wait_event_interruptible(q->throttle_wait, atomic_read(&q->available) >= need);
+ atomic_sub(need, &q->available);
+ }
/*
* Resolve the mapping until finished. (drivers are
* still free to implement/resolve their own stacking
@@ -3234,7 +3241,6 @@ static inline void __generic_make_reques
do {
char b[BDEVNAME_SIZE];

- q = bdev_get_queue(bio->bi_bdev);
if (!q) {
printk(KERN_ERR
"generic_make_request: Trying to access "
--- 2.6.24-rc3-mm.clean/drivers/md/dm.c 2007-12-04 14:46:04.000000000 -0800
+++ 2.6.24-rc3-mm/drivers/md/dm.c 2007-12-04 23:31:41.000000000 -0800
@@ -889,6 +889,11 @@ static int dm_any_congested(void *conges
return r;
}

+static unsigned dm_metric(struct bio *bio)
+{
+ return bio->bi_vcnt;
+}
+
/*-----------------------------------------------------------------
* An IDR is used to keep track of allocated minor numbers.
*---------------------------------------------------------------*/
@@ -967,6 +972,7 @@ out:

static struct block_device_operations dm_blk_dops;

+#define DEFAULT_THROTTLE_CAPACITY 1000
/*
* Allocate and initialise a blank device with a given minor.
*/
@@ -1009,6 +1015,11 @@ static struct mapped_device *alloc_dev(i
goto bad1_free_minor;

md->queue->queuedata = md;
+ md->queue->metric = dm_metric;
+ /* A dm device constructor may change the throttle capacity */
+ atomic_set(&md->queue->available, md->queue->capacity = DEFAULT_THROTTLE_CAPACITY);
+ init_waitqueue_head(&md->queue->throttle_wait);
+
md->queue->backing_dev_info.congested_fn = dm_any_congested;
md->queue->backing_dev_info.congested_data = md;
blk_queue_make_request(md->queue, dm_request);
--- 2.6.24-rc3-mm.clean/fs/bio.c 2007-12-04 14:38:47.000000000 -0800
+++ 2.6.24-rc3-mm/fs/bio.c 2007-12-04 23:31:41.000000000 -0800
@@ -1007,6 +1007,13 @@ void bio_endio(struct bio *bio, int erro
else if (!test_bit(BIO_UPTODATE, &bio->bi_flags))
error = -EIO;

+ if (bio->bi_throttle) {
+ struct request_queue *q = bio->bi_queue;
+ bio->bi_throttle = 0; /* or detect multiple endio and err? */
+ atomic_add(bio->bi_throttle, &q->available);
+ wake_up(&q->throttle_wait);
+ }
+
if (bio->bi_end_io)
bio->bi_end_io(bio, error);
}
--- 2.6.24-rc3-mm.clean/include/linux/bio.h 2007-12-04 14:39:31.000000000 -0800
+++ 2.6.24-rc3-mm/include/linux/bio.h 2007-12-04 23:31:41.000000000 -0800
@@ -111,6 +111,9 @@ struct bio {
bio_end_io_t *bi_end_io;
atomic_t bi_cnt; /* pin count */

+ struct request_queue *bi_queue; /* for throttling */
+ unsigned bi_throttle; /* throttle metric */
+
void *bi_private;

bio_destructor_t *bi_destructor; /* destructor */
--- 2.6.24-rc3-mm.clean/include/linux/blkdev.h 2007-12-04 14:47:18.000000000 -0800
+++ 2.6.24-rc3-mm/include/linux/blkdev.h 2007-12-04 23:31:41.000000000 -0800
@@ -383,6 +383,10 @@ struct request_queue
struct work_struct unplug_work;

struct backing_dev_info backing_dev_info;
+ unsigned (*metric)(struct bio *bio); /* bio throttle metric */
+ wait_queue_head_t throttle_wait;
+ atomic_t available;
+ unsigned capacity;

/*
* The queue owner gets to use this for whatever they like.