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

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