Re: [patch for playing] 2.5.65 patch to support > 256 disks

Jens Axboe
2003-03-25T11:23:07Z

On Tue, Mar 25 2003, Jens Axboe wrote:
> Here's a patch that makes the request allocation (and io scheduler
> private data) dynamic, with upper and lower bounds of 4 and 256
> respectively. The numbers are a bit random - the 4 will allow us to make
> progress, but it might be a smidgen too low. Perhaps 8 would be good.
> 256 is twice as much as before, but that should be alright as long as
> the io scheduler copes. BLKDEV_MAX_RQ and BLKDEV_MIN_RQ control these
> two variables.
>
> We loose the old batching functionality, for now. I can resurrect that
> if needed. It's a rough fit with the mempool, it doesn't _quite_ fit our
> needs here. I'll probably end up doing a specialised block pool scheme
> for this.
>
> Hasn't been tested all that much, it boots though :-)

Here's a version with better lock handling. We drop the queue_lock for
most parts of __make_request(), except the actual io scheduler calls.

Patch is against 2.5.66-BK as of today.

drivers/block/deadline-iosched.c | 86 ++++++-------
drivers/block/elevator.c | 18 ++
drivers/block/ll_rw_blk.c | 245 ++++++++++++---------------------------
include/linux/blkdev.h | 12 +
include/linux/elevator.h | 7 +
5 files changed, 154 insertions(+), 214 deletions(-)

===== drivers/block/deadline-iosched.c 1.17 vs edited =====
--- 1.17/drivers/block/deadline-iosched.c Fri Mar 14 16:55:04 2003
+++ edited/drivers/block/deadline-iosched.c Tue Mar 25 11:05:37 2003
@@ -71,6 +71,8 @@
int fifo_batch;
int writes_starved;
int front_merges;
+
+ mempool_t *drq_pool;
};

/*
@@ -673,28 +675,11 @@
static void deadline_exit(request_queue_t *q, elevator_t *e)
{
struct deadline_data *dd = e->elevator_data;
- struct deadline_rq *drq;
- struct request *rq;
- int i;

BUG_ON(!list_empty(&dd->fifo_list[READ]));
BUG_ON(!list_empty(&dd->fifo_list[WRITE]));

- for (i = READ; i <= WRITE; i++) {
- struct request_list *rl = &q->rq[i];
- struct list_head *entry;
-
- list_for_each(entry, &rl->free) {
- rq = list_entry_rq(entry);
-
- if ((drq = RQ_DATA(rq)) == NULL)
- continue;
-
- rq->elevator_private = NULL;
- kmem_cache_free(drq_pool, drq);
- }
- }
-
+ mempool_destroy(dd->drq_pool);
kfree(dd->hash);
kfree(dd);
}
@@ -706,9 +691,7 @@
static int deadline_init(request_queue_t *q, elevator_t *e)
{
struct deadline_data *dd;
- struct deadline_rq *drq;
- struct request *rq;
- int i, ret = 0;
+ int i;

if (!drq_pool)
return -ENOMEM;
@@ -724,6 +707,13 @@
return -ENOMEM;
}

+ dd->drq_pool = mempool_create(BLKDEV_MIN_RQ, mempool_alloc_slab, mempool_free_slab, drq_pool);
+ if (!dd->drq_pool) {
+ kfree(dd->hash);
+ kfree(dd);
+ return -ENOMEM;
+ }
+
for (i = 0; i < DL_HASH_ENTRIES; i++)
INIT_LIST_HEAD(&dd->hash[i]);

@@ -739,33 +729,41 @@
dd->front_merges = 1;
dd->fifo_batch = fifo_batch;
e->elevator_data = dd;
+ return 0;
+}

- for (i = READ; i <= WRITE; i++) {
- struct request_list *rl = &q->rq[i];
- struct list_head *entry;
-
- list_for_each(entry, &rl->free) {
- rq = list_entry_rq(entry);
-
- drq = kmem_cache_alloc(drq_pool, GFP_KERNEL);
- if (!drq) {
- ret = -ENOMEM;
- break;
- }
+static void deadline_put_request(request_queue_t *q, struct request *rq)
+{
+ struct deadline_data *dd = q->elevator.elevator_data;
+ struct deadline_rq *drq = RQ_DATA(rq);

- memset(drq, 0, sizeof(*drq));
- INIT_LIST_HEAD(&drq->fifo);
- INIT_LIST_HEAD(&drq->hash);
- RB_CLEAR(&drq->rb_node);
- drq->request = rq;
- rq->elevator_private = drq;
- }
+ if (drq) {
+ mempool_free(drq, dd->drq_pool);
+ rq->elevator_private = NULL;
}
+}
+
+static int
+deadline_set_request(request_queue_t *q, struct request *rq, int gfp_mask)
+{
+ struct deadline_data *dd = q->elevator.elevator_data;
+ struct deadline_rq *drq;

- if (ret)
- deadline_exit(q, e);
+ drq = mempool_alloc(dd->drq_pool, gfp_mask);
+ if (drq) {
+ RB_CLEAR(&drq->rb_node);
+ drq->request = rq;

- return ret;
+ INIT_LIST_HEAD(&drq->hash);
+ drq->hash_valid_count = 0;
+
+ INIT_LIST_HEAD(&drq->fifo);
+
+ rq->elevator_private = drq;
+ return 0;
+ }
+
+ return 1;
}

/*
@@ -916,6 +914,8 @@
.elevator_queue_empty_fn = deadline_queue_empty,
.elevator_former_req_fn = deadline_former_request,
.elevator_latter_req_fn = deadline_latter_request,
+ .elevator_set_req_fn = deadline_set_request,
+ .elevator_put_req_fn = deadline_put_request,
.elevator_init_fn = deadline_init,
.elevator_exit_fn = deadline_exit,

===== drivers/block/elevator.c 1.40 vs edited =====
--- 1.40/drivers/block/elevator.c Sun Feb 16 12:32:35 2003
+++ edited/drivers/block/elevator.c Tue Mar 25 11:04:01 2003
@@ -408,6 +408,24 @@
return NULL;
}

+int elv_set_request(request_queue_t *q, struct request *rq, int gfp_mask)
+{
+ elevator_t *e = &q->elevator;
+
+ if (e->elevator_set_req_fn)
+ return e->elevator_set_req_fn(q, rq, gfp_mask);
+
+ return 0;
+}
+
+void elv_put_request(request_queue_t *q, struct request *rq)
+{
+ elevator_t *e = &q->elevator;
+
+ if (e->elevator_put_req_fn)
+ e->elevator_put_req_fn(q, rq);
+}
+
int elv_register_queue(struct gendisk *disk)
{
request_queue_t *q = disk->queue;
===== drivers/block/ll_rw_blk.c 1.161 vs edited =====
--- 1.161/drivers/block/ll_rw_blk.c Mon Mar 24 02:56:03 2003
+++ edited/drivers/block/ll_rw_blk.c Tue Mar 25 12:20:16 2003
@@ -48,12 +48,6 @@
*/
static int queue_nr_requests;

-/*
- * How many free requests must be available before we wake a process which
- * is waiting for a request?
- */
-static int batch_requests;
-
unsigned long blk_max_low_pfn, blk_max_pfn;
int blk_nohighio = 0;

@@ -1118,26 +1112,6 @@
spin_unlock_irq(&blk_plug_lock);
}

-static int __blk_cleanup_queue(struct request_list *list)
-{
- struct list_head *head = &list->free;
- struct request *rq;
- int i = 0;
-
- while (!list_empty(head)) {
- rq = list_entry(head->next, struct request, queuelist);
- list_del_init(&rq->queuelist);
- kmem_cache_free(request_cachep, rq);
- i++;
- }
-
- if (i != list->count)
- printk("request list leak!\n");
-
- list->count = 0;
- return i;
-}
-
/**
* blk_cleanup_queue: - release a &request_queue_t when it is no longer needed
* @q: the request queue to be released
@@ -1154,18 +1128,14 @@
**/
void blk_cleanup_queue(request_queue_t * q)
{
- int count = (queue_nr_requests*2);
+ struct request_list *rl = &q->rq;

elevator_exit(q);

- count -= __blk_cleanup_queue(&q->rq[READ]);
- count -= __blk_cleanup_queue(&q->rq[WRITE]);
-
del_timer_sync(&q->unplug_timer);
flush_scheduled_work();

- if (count)
- printk("blk_cleanup_queue: leaked requests (%d)\n", count);
+ mempool_destroy(rl->rq_pool);

if (blk_queue_tagged(q))
blk_queue_free_tags(q);
@@ -1175,42 +1145,17 @@

static int blk_init_free_list(request_queue_t *q)
{
- struct request_list *rl;
- struct request *rq;
- int i;
+ struct request_list *rl = &q->rq;

- INIT_LIST_HEAD(&q->rq[READ].free);
- INIT_LIST_HEAD(&q->rq[WRITE].free);
- q->rq[READ].count = 0;
- q->rq[WRITE].count = 0;
+ rl->count[READ] = BLKDEV_MAX_RQ;
+ rl->count[WRITE] = BLKDEV_MAX_RQ;

- /*
- * Divide requests in half between read and write
- */
- rl = &q->rq[READ];
- for (i = 0; i < (queue_nr_requests*2); i++) {
- rq = kmem_cache_alloc(request_cachep, SLAB_KERNEL);
- if (!rq)
- goto nomem;
-
- /*
- * half way through, switch to WRITE list
- */
- if (i == queue_nr_requests)
- rl = &q->rq[WRITE];
+ rl->rq_pool = mempool_create(BLKDEV_MIN_RQ, mempool_alloc_slab, mempool_free_slab, request_cachep);

- memset(rq, 0, sizeof(struct request));
- rq->rq_status = RQ_INACTIVE;
- list_add(&rq->queuelist, &rl->free);
- rl->count++;
- }
+ if (!rl->rq_pool)
+ return -ENOMEM;

- init_waitqueue_head(&q->rq[READ].wait);
- init_waitqueue_head(&q->rq[WRITE].wait);
return 0;
-nomem:
- blk_cleanup_queue(q);
- return 1;
}

static int __make_request(request_queue_t *, struct bio *);
@@ -1277,34 +1222,62 @@
return 0;
}

+static inline void blk_free_request(request_queue_t *q, struct request *rq)
+{
+ elv_put_request(q, rq);
+ mempool_free(rq, q->rq.rq_pool);
+}
+
+static inline struct request *blk_alloc_request(request_queue_t *q,int gfp_mask)
+{
+ struct request *rq = mempool_alloc(q->rq.rq_pool, gfp_mask);
+
+ if (rq) {
+ if (!elv_set_request(q, rq, gfp_mask))
+ return rq;
+
+ mempool_free(rq, q->rq.rq_pool);
+ }
+
+ return NULL;
+}
+
#define blkdev_free_rq(list) list_entry((list)->next, struct request, queuelist)
/*
- * Get a free request. queue lock must be held and interrupts
- * disabled on the way in.
+ * Get a free request, queue_lock must not be held
*/
-static struct request *get_request(request_queue_t *q, int rw)
+static struct request *get_request(request_queue_t *q, int rw, int gfp_mask)
{
struct request *rq = NULL;
- struct request_list *rl = q->rq + rw;
+ struct request_list *rl = &q->rq;

- if (!list_empty(&rl->free)) {
- rq = blkdev_free_rq(&rl->free);
- list_del_init(&rq->queuelist);
- rq->ref_count = 1;
- rl->count--;
- if (rl->count < queue_congestion_on_threshold())
+ /*
+ * known racy, ok though
+ */
+ if (!rl->count[rw])
+ return NULL;
+
+ rq = blk_alloc_request(q, gfp_mask);
+ if (rq) {
+ spin_lock_irq(q->queue_lock);
+ rl->count[rw]--;
+ if (rl->count[rw] < queue_congestion_on_threshold())
set_queue_congested(q, rw);
+ spin_unlock_irq(q->queue_lock);
+
+ INIT_LIST_HEAD(&rq->queuelist);
rq->flags = 0;
- rq->rq_status = RQ_ACTIVE;
rq->errors = 0;
- rq->special = NULL;
- rq->buffer = NULL;
- rq->data = NULL;
- rq->sense = NULL;
- rq->waiting = NULL;
+ rq->rq_status = RQ_ACTIVE;
rq->bio = rq->biotail = NULL;
+ rq->buffer = NULL;
+ rq->ref_count = 1;
rq->q = q;
rq->rl = rl;
+ rq->special = NULL;
+ rq->data = NULL;
+ rq->waiting = NULL;
+ rq->sense = NULL;
}

return rq;
@@ -1316,7 +1289,7 @@
static struct request *get_request_wait(request_queue_t *q, int rw)
{
DEFINE_WAIT(wait);
- struct request_list *rl = &q->rq[rw];
+ struct request_list *rl = &q->rq;
struct request *rq;

spin_lock_prefetch(q->queue_lock);
@@ -1325,64 +1298,24 @@
do {
int block = 0;

- prepare_to_wait_exclusive(&rl->wait, &wait,
- TASK_UNINTERRUPTIBLE);
spin_lock_irq(q->queue_lock);
- if (!rl->count)
+ if (!rl->count[rw])
block = 1;
spin_unlock_irq(q->queue_lock);

if (block)
io_schedule();
- finish_wait(&rl->wait, &wait);

- spin_lock_irq(q->queue_lock);
- rq = get_request(q, rw);
- spin_unlock_irq(q->queue_lock);
+ rq = get_request(q, rw, GFP_NOIO);
} while (rq == NULL);
return rq;
}

struct request *blk_get_request(request_queue_t *q, int rw, int gfp_mask)
{
- struct request *rq;
-
- BUG_ON(rw != READ && rw != WRITE);
-
- spin_lock_irq(q->queue_lock);
- rq = get_request(q, rw);
- spin_unlock_irq(q->queue_lock);
-
- if (!rq && (gfp_mask & __GFP_WAIT))
- rq = get_request_wait(q, rw);
-
- if (rq) {
- rq->flags = 0;
- rq->buffer = NULL;
- rq->bio = rq->biotail = NULL;
- rq->waiting = NULL;
- }
- return rq;
-}
-
-/*
- * Non-locking blk_get_request variant, for special requests from drivers.
- */
-struct request *__blk_get_request(request_queue_t *q, int rw)
-{
- struct request *rq;
-
BUG_ON(rw != READ && rw != WRITE);

- rq = get_request(q, rw);
-
- if (rq) {
- rq->flags = 0;
- rq->buffer = NULL;
- rq->bio = rq->biotail = NULL;
- rq->waiting = NULL;
- }
- return rq;
+ return get_request(q, rw, gfp_mask);
}

/**
@@ -1499,6 +1432,9 @@
disk->stamp_idle = now;
}

+/*
+ * queue lock must be held
+ */
void __blk_put_request(request_queue_t *q, struct request *req)
{
struct request_list *rl = req->rl;
@@ -1508,34 +1444,26 @@
if (unlikely(!q))
return;

- req->rq_status = RQ_INACTIVE;
- req->q = NULL;
- req->rl = NULL;
-
/*
* Request may not have originated from ll_rw_blk. if not,
* it didn't come out of our reserved rq pools
*/
if (rl) {
- int rw = 0;
+ int rw = rq_data_dir(req);

BUG_ON(!list_empty(&req->queuelist));

- list_add(&req->queuelist, &rl->free);
+ blk_free_request(q, req);

- if (rl == &q->rq[WRITE])
- rw = WRITE;
- else if (rl == &q->rq[READ])
- rw = READ;
- else
- BUG();
-
- rl->count++;
- if (rl->count >= queue_congestion_off_threshold())
+ rl->count[rw]++;
+ if (rl->count[rw] >= queue_congestion_off_threshold())
clear_queue_congested(q, rw);
- if (rl->count >= batch_requests && waitqueue_active(&rl->wait))
- wake_up(&rl->wait);
}
+
+ req->rq_status = RQ_INACTIVE;
+ req->q = NULL;
+ req->rl = NULL;
+ req->elevator_private = NULL;
}

void blk_put_request(struct request *req)
@@ -1694,9 +1622,9 @@

barrier = test_bit(BIO_RW_BARRIER, &bio->bi_rw);

- spin_lock_irq(q->queue_lock);
again:
insert_here = NULL;
+ spin_lock_irq(q->queue_lock);

if (blk_queue_empty(q)) {
blk_plug_device(q);
@@ -1769,12 +1697,12 @@
* a free slot.
*/
get_rq:
+ spin_unlock_irq(q->queue_lock);
+
if (freereq) {
req = freereq;
freereq = NULL;
- } else if ((req = get_request(q, rw)) == NULL) {
- spin_unlock_irq(q->queue_lock);
-
+ } else if ((req = get_request(q, rw, GFP_NOIO)) == NULL) {
/*
* READA bit set
*/
@@ -1782,7 +1710,6 @@
goto end_io;

freereq = get_request_wait(q, rw);
- spin_lock_irq(q->queue_lock);
goto again;
}

@@ -1809,19 +1736,20 @@
req->bio = req->biotail = bio;
req->rq_disk = bio->bi_bdev->bd_disk;
req->start_time = jiffies;
+
+ spin_lock_irq(q->queue_lock);
add_request(q, req, insert_here);
out:
if (freereq)
__blk_put_request(q, freereq);

if (blk_queue_plugged(q)) {
- int nr_queued = (queue_nr_requests - q->rq[0].count) +
- (queue_nr_requests - q->rq[1].count);
+ int nr_queued = (queue_nr_requests - q->rq.count[0]) +
+ (queue_nr_requests - q->rq.count[1]);
if (nr_queued == q->unplug_thresh)
__generic_unplug_device(q);
}
spin_unlock_irq(q->queue_lock);
-
return 0;

end_io:
@@ -2183,7 +2111,6 @@

int __init blk_dev_init(void)
{
- int total_ram = nr_free_pages() << (PAGE_SHIFT - 10);
int i;

request_cachep = kmem_cache_create("blkdev_requests",
@@ -2191,24 +2118,11 @@
if (!request_cachep)
panic("Can't create request pool slab cache\n");

- /*
- * Free request slots per queue. One per quarter-megabyte.
- * We use this many requests for reads, and this many for writes.
- */
- queue_nr_requests = (total_ram >> 9) & ~7;
- if (queue_nr_requests < 16)
- queue_nr_requests = 16;
- if (queue_nr_requests > 128)
- queue_nr_requests = 128;
-
- batch_requests = queue_nr_requests / 8;
- if (batch_requests > 8)
- batch_requests = 8;
+ queue_nr_requests = BLKDEV_MAX_RQ;

printk("block request queues:\n");
- printk(" %d requests per read queue\n", queue_nr_requests);
- printk(" %d requests per write queue\n", queue_nr_requests);
- printk(" %d requests per batch\n", batch_requests);
+ printk(" %d/%d requests per read queue\n", BLKDEV_MIN_RQ, queue_nr_requests);
+ printk(" %d/%d requests per write queue\n", BLKDEV_MIN_RQ, queue_nr_requests);
printk(" enter congestion at %d\n", queue_congestion_on_threshold());
printk(" exit congestion at %d\n", queue_congestion_off_threshold());

@@ -2250,7 +2164,6 @@
EXPORT_SYMBOL(blk_phys_contig_segment);
EXPORT_SYMBOL(blk_hw_contig_segment);
EXPORT_SYMBOL(blk_get_request);
-EXPORT_SYMBOL(__blk_get_request);
EXPORT_SYMBOL(blk_put_request);
EXPORT_SYMBOL(blk_insert_request);

===== include/linux/blkdev.h 1.98 vs edited =====
--- 1.98/include/linux/blkdev.h Tue Feb 18 11:29:00 2003
+++ edited/include/linux/blkdev.h Tue Mar 25 12:12:20 2003
@@ -10,6 +10,7 @@
#include <linux/pagemap.h>
#include <linux/backing-dev.h>
#include <linux/wait.h>
+#include <linux/mempool.h>

#include <asm/scatterlist.h>

@@ -18,10 +19,12 @@
struct elevator_s;
typedef struct elevator_s elevator_t;

+#define BLKDEV_MIN_RQ 4
+#define BLKDEV_MAX_RQ 256
+
struct request_list {
- unsigned int count;
- struct list_head free;
- wait_queue_head_t wait;
+ int count[2];
+ mempool_t *rq_pool;
};

/*
@@ -180,7 +183,7 @@
/*
* the queue request freelist, one for reads and one for writes
*/
- struct request_list rq[2];
+ struct request_list rq;

request_fn_proc *request_fn;
merge_request_fn *back_merge_fn;
@@ -330,7 +333,6 @@
extern void blk_attempt_remerge(request_queue_t *, struct request *);
extern void __blk_attempt_remerge(request_queue_t *, struct request *);
extern struct request *blk_get_request(request_queue_t *, int, int);
-extern struct request *__blk_get_request(request_queue_t *, int);
extern void blk_put_request(struct request *);
extern void blk_insert_request(request_queue_t *, struct request *, int, void *);
extern void blk_plug_device(request_queue_t *);
===== include/linux/elevator.h 1.18 vs edited =====
--- 1.18/include/linux/elevator.h Sun Jan 12 15:10:40 2003
+++ edited/include/linux/elevator.h Tue Mar 25 11:03:42 2003
@@ -15,6 +15,8 @@
typedef void (elevator_remove_req_fn) (request_queue_t *, struct request *);
typedef struct request *(elevator_request_list_fn) (request_queue_t *, struct request *);
typedef struct list_head *(elevator_get_sort_head_fn) (request_queue_t *, struct request *);
+typedef int (elevator_set_req_fn) (request_queue_t *, struct request *, int);
+typedef void (elevator_put_req_fn) (request_queue_t *, struct request *);

typedef int (elevator_init_fn) (request_queue_t *, elevator_t *);
typedef void (elevator_exit_fn) (request_queue_t *, elevator_t *);
@@ -34,6 +36,9 @@
elevator_request_list_fn *elevator_former_req_fn;
elevator_request_list_fn *elevator_latter_req_fn;

+ elevator_set_req_fn *elevator_set_req_fn;
+ elevator_put_req_fn *elevator_put_req_fn;
+
elevator_init_fn *elevator_init_fn;
elevator_exit_fn *elevator_exit_fn;

@@ -58,6 +63,8 @@
extern struct request *elv_latter_request(request_queue_t *, struct request *);
extern int elv_register_queue(struct gendisk *);
extern void elv_unregister_queue(struct gendisk *);
+extern int elv_set_request(request_queue_t *, struct request *, int);
+extern void elv_put_request(request_queue_t *, struct request *);

#define __elv_add_request_pos(q, rq, pos) \
(q)->elevator.elevator_add_req_fn((q), (rq), (pos))

--
Jens Axboe