/* * Anticipatory & deadline i/o scheduler. * * Copyright (C) 2002 Jens Axboe <axboe@suse.de> * Nick Piggin <nickpiggin@yahoo.com.au> * */ #include <linux/kernel.h> #include <linux/fs.h> #include <linux/blkdev.h> #include <linux/elevator.h> #include <linux/bio.h> #include <linux/config.h> #include <linux/module.h> #include <linux/slab.h> #include <linux/init.h> #include <linux/compiler.h> #include <linux/hash.h> #include <linux/rbtree.h> #include <linux/interrupt.h> #define REQ_SYNC 1 #define REQ_ASYNC 0 /* * See Documentation/block/as-iosched.txt */ /* * max time before a read is submitted. */ #define default_read_expire (HZ / 8) /* * ditto for writes, these limits are not hard, even * if the disk is capable of satisfying them. */ #define default_write_expire (HZ / 4) /* * read_batch_expire describes how long we will allow a stream of reads to * persist before looking to see whether it is time to switch over to writes. */ #define default_read_batch_expire (HZ / 2) /* * write_batch_expire describes how long we want a stream of writes to run for. * This is not a hard limit, but a target we set for the auto-tuning thingy. * See, the problem is: we can send a lot of writes to disk cache / TCQ in * a short amount of time... */ #define default_write_batch_expire (HZ / 8) /* * max time we may wait to anticipate a read (default around 6ms) */ #define default_antic_expire ((HZ / 150) ? HZ / 150 : 1) /* * Keep track of up to 20ms thinktimes. We can go as big as we like here, * however huge values tend to interfere and not decay fast enough. A program * might be in a non-io phase of operation. Waiting on user input for example, * or doing a lengthy computation. A small penalty can be justified there, and * will still catch out those processes that constantly have large thinktimes. */ #define MAX_THINKTIME (HZ/50UL) /* Bits in as_io_context.state */ enum as_io_states { AS_TASK_RUNNING=0, /* Process has not exited */ AS_TASK_IOSTARTED, /* Process has started some IO */ AS_TASK_IORUNNING, /* Process has completed some IO */ }; enum anticipation_status { ANTIC_OFF=0, /* Not anticipating (normal operation) */ ANTIC_WAIT_REQ, /* The last read has not yet completed */ ANTIC_WAIT_NEXT, /* Currently anticipating a request vs last read (which has completed) */ ANTIC_FINISHED, /* Anticipating but have found a candidate * or timed out */ }; struct as_data { /* * run time data */ struct request_queue *q; /* the "owner" queue */ /* * requests (as_rq s) are present on both sort_list and fifo_list */ struct rb_root sort_list[2]; struct list_head fifo_list[2]; struct as_rq *next_arq[2]; /* next in sort order */ sector_t last_sector[2]; /* last REQ_SYNC & REQ_ASYNC sectors */ struct list_head *hash; /* request hash */ unsigned long exit_prob; /* probability a task will exit while being waited on */ unsigned long exit_no_coop; /* probablility an exited task will not be part of a later cooperating request */ unsigned long new_ttime_total; /* mean thinktime on new proc */ unsigned long new_ttime_mean; u64 new_seek_total; /* mean seek on new proc */ sector_t new_seek_mean; unsigned long current_batch_expires; unsigned long last_check_fifo[2]; int changed_batch; /* 1: waiting for old batch to end */ int new_batch; /* 1: waiting on first read complete */ int batch_data_dir; /* current batch REQ_SYNC / REQ_ASYNC */ int write_batch_count; /* max # of reqs in a write batch */ int current_write_count; /* how many requests left this batch */ int write_batch_idled; /* has the write batch gone idle? */ mempool_t *arq_pool; enum anticipation_status antic_status; unsigned long antic_start; /* jiffies: when it started */ struct timer_list antic_timer; /* anticipatory scheduling timer */ struct work_struct antic_work; /* Deferred unplugging */ struct io_context *io_context; /* Identify the expected process */ int ioc_finished; /* IO associated with io_context is finished */ int nr_dispatched; /* * settings that change how the i/o scheduler behaves */ unsigned long fifo_expire[2]; unsigned long batch_expire[2]; unsigned long antic_expire; }; #define list_entry_fifo(ptr) list_entry((ptr), struct as_rq, fifo) /* * per-request data. */ enum arq_state { AS_RQ_NEW=0, /* New - not referenced and not on any lists */ AS_RQ_QUEUED, /* In the request queue. It belongs to the scheduler */ AS_RQ_DISPATCHED, /* On the dispatch list. It belongs to the driver now */ AS_RQ_PRESCHED, /* Debug poisoning for requests being used */ AS_RQ_REMOVED, AS_RQ_MERGED, AS_RQ_POSTSCHED, /* when they shouldn't be */ }; struct as_rq { /* * rbtree index, key is the starting offset */ struct rb_node rb_node; sector_t rb_key; struct request *request; struct io_context *io_context; /* The submitting task */ /* * request hash, key is the ending offset (for back merge lookup) */ struct list_head hash; unsigned int on_hash; /* * expire fifo */ struct list_head fifo; unsigned long expires; unsigned int is_sync; enum arq_state state; }; #define RQ_DATA(rq) ((struct as_rq *) (rq)->elevator_private) static kmem_cache_t *arq_pool; static atomic_t ioc_count = ATOMIC_INIT(0); static struct completion *ioc_gone; static void as_move_to_dispatch(struct as_data *ad, struct as_rq *arq); static void as_antic_stop(struct as_data *ad); /* * IO Context helper functions */ /* Called to deallocate the as_io_context */ static void free_as_io_context(struct as_io_context *aic) { kfree(aic); if (atomic_dec_and_test(&ioc_count) && ioc_gone) complete(ioc_gone); } static void as_trim(struct io_context *ioc) { if (ioc->aic) free_as_io_context(ioc->aic); ioc->aic = NULL; } /* Called when the task exits */ static void exit_as_io_context(struct as_io_context *aic) { WARN_ON(!test_bit(AS_TASK_RUNNING, &aic->state)); clear_bit(AS_TASK_RUNNING, &aic->state); } static struct as_io_context *alloc_as_io_context(void) { struct as_io_context *ret; ret = kmalloc(sizeof(*ret), GFP_ATOMIC); if (ret) { ret->dtor = free_as_io_context; ret->exit = exit_as_io_context; ret->state = 1 << AS_TASK_RUNNING; atomic_set(&ret->nr_queued, 0); atomic_set(&ret->nr_dispatched, 0); spin_lock_init(&ret->lock); ret->ttime_total = 0; ret->ttime_samples = 0; ret->ttime_mean = 0; ret->seek_total = 0; ret->seek_samples = 0; ret->seek_mean = 0; atomic_inc(&ioc_count); } return ret; } /* * If the current task has no AS IO context then create one and initialise it. * Then take a ref on the task's io context and return it. */ static struct io_context *as_get_io_context(void) { struct io_context *ioc = get_io_context(GFP_ATOMIC); if (ioc && !ioc->aic) { ioc->aic = alloc_as_io_context(); if (!ioc->aic) { put_io_context(ioc); ioc = NULL; } } return ioc; } static void as_put_io_context(struct as_rq *arq) { struct as_io_context *aic; if (unlikely(!arq->io_context)) return; aic = arq->io_context->aic; if (arq->is_sync == REQ_SYNC && aic) { spin_lock(&aic->lock); set_bit(AS_TASK_IORUNNING, &aic->state); aic->last_end_request = jiffies; spin_unlock(&aic->lock); } put_io_context(arq->io_context); } /* * the back merge hash support functions */ static const int as_hash_shift = 6; #define AS_HASH_BLOCK(sec) ((sec) >> 3) #define AS_HASH_FN(sec) (hash_long(AS_HASH_BLOCK((sec)), as_hash_shift)) #define AS_HASH_ENTRIES (1 << as_hash_shift) #define rq_hash_key(rq) ((rq)->sector + (rq)->nr_sectors) #define list_entry_hash(ptr) list_entry((ptr), struct as_rq, hash) static inline void __as_del_arq_hash(struct as_rq *arq) { arq->on_hash = 0; list_del_init(&arq->hash); } static inline void as_del_arq_hash(struct as_rq *arq) { if (arq->on_hash) __as_del_arq_hash(arq); } static void as_add_arq_hash(struct as_data *ad, struct as_rq *arq) { struct request *rq = arq->request; BUG_ON(arq->on_hash); arq->on_hash = 1; list_add(&arq->hash, &ad->hash[AS_HASH_FN(rq_hash_key(rq))]); } /* * move hot entry to front of chain */ static inline void as_hot_arq_hash(struct as_data *ad, struct as_rq *arq) { struct request *rq = arq->request; struct list_head *head = &ad->hash[AS_HASH_FN(rq_hash_key(rq))]; if (!arq->on_hash) { WARN_ON(1); return; } if (arq->hash.prev != head) { list_del(&arq->hash); list_add(&arq->hash, head); } } static struct request *as_find_arq_hash(struct as_data *ad, sector_t offset) { struct list_head *hash_list = &ad->hash[AS_HASH_FN(offset)]; struct list_head *entry, *next = hash_list->next; while ((entry = next) != hash_list) { struct as_rq *arq = list_entry_hash(entry); struct request *__rq = arq->request; next = entry->next; BUG_ON(!arq->on_hash); if (!rq_mergeable(__rq)) { as_del_arq_hash(arq); continue; } if (rq_hash_key(__rq) == offset) return __rq; } return NULL; } /* * rb tree support functions */ #define RB_NONE (2) #define RB_EMPTY(root) ((root)->rb_node == NULL) #define ON_RB(node) ((node)->rb_color != RB_NONE) #define RB_CLEAR(node) ((node)->rb_color = RB_NONE) #define rb_entry_arq(node) rb_entry((node), struct as_rq, rb_node) #define ARQ_RB_ROOT(ad, arq) (&(ad)->sort_list[(arq)->is_sync]) #define rq_rb_key(rq) (rq)->sector /* * as_find_first_arq finds the first (lowest sector numbered) request * for the specified data_dir. Used to sweep back to the start of the disk * (1-way elevator) after we process the last (highest sector) request. */ static struct as_rq *as_find_first_arq(struct as_data *ad, int data_dir) { struct rb_node *n = ad->sort_list[data_dir].rb_node; if (n == NULL) return NULL; for (;;) { if (n->rb_left == NULL) return rb_entry_arq(n); n = n->rb_left; } } /* * Add the request to the rb tree if it is unique. If there is an alias (an * existing request against the same sector), which can happen when using * direct IO, then return the alias. */ static struct as_rq *__as_add_arq_rb(struct as_data *ad, struct as_rq *arq) { struct rb_node **p = &ARQ_RB_ROOT(ad, arq)->rb_node; struct rb_node *parent = NULL; struct as_rq *__arq; struct request *rq = arq->request; arq->rb_key = rq_rb_key(rq); while (*p) { parent = *p; __arq = rb_entry_arq(parent); if (arq->rb_key < __arq->rb_key) p = &(*p)->rb_left; else if (arq->rb_key > __arq->rb_key) p = &(*p)->rb_right; else return __arq; } rb_link_node(&arq->rb_node, parent, p); rb_insert_color(&arq->rb_node, ARQ_RB_ROOT(ad, arq)); return NULL; } static void as_add_arq_rb(struct as_data *ad, struct as_rq *arq) { struct as_rq *alias; while ((unlikely(alias = __as_add_arq_rb(ad, arq)))) { as_move_to_dispatch(ad, alias); as_antic_stop(ad); } } static inline void as_del_arq_rb(struct as_data *ad, struct as_rq *arq) { if (!ON_RB(&arq->rb_node)) { WARN_ON(1); return; } rb_erase(&arq->rb_node, ARQ_RB_ROOT(ad, arq)); RB_CLEAR(&arq->rb_node); } static struct request * as_find_arq_rb(struct as_data *ad, sector_t sector, int data_dir) { struct rb_node *n = ad->sort_list[data_dir].rb_node; struct as_rq *arq; while (n) { arq = rb_entry_arq(n); if (sector < arq->rb_key) n = n->rb_left; else if (sector > arq->rb_key) n = n->rb_right; else return arq->request; } return NULL; } /* * IO Scheduler proper */ #define MAXBACK (1024 * 1024) /* * Maximum distance the disk will go backward * for a request. */ #define BACK_PENALTY 2 /* * as_choose_req selects the preferred one of two requests of the same data_dir * ignoring time - eg. timeouts, which is the job of as_dispatch_request */ static struct as_rq * as_choose_req(struct as_data *ad, struct as_rq *arq1, struct as_rq *arq2) { int data_dir; sector_t last, s1, s2, d1, d2; int r1_wrap=0, r2_wrap=0; /* requests are behind the disk head */ const sector_t maxback = MAXBACK; if (arq1 == NULL || arq1 == arq2) return arq2; if (arq2 == NULL) return arq1; data_dir = arq1->is_sync; last = ad->last_sector[data_dir]; s1 = arq1->request->sector; s2 = arq2->request->sector; BUG_ON(data_dir != arq2->is_sync); /* * Strict one way elevator _except_ in the case where we allow * short backward seeks which are biased as twice the cost of a * similar forward seek. */ if (s1 >= last) d1 = s1 - last; else if (s1+maxback >= last) d1 = (last - s1)*BACK_PENALTY; else { r1_wrap = 1; d1 = 0; /* shut up, gcc */ } if (s2 >= last) d2 = s2 - last; else if (s2+maxback >= last) d2 = (last - s2)*BACK_PENALTY; else { r2_wrap = 1; d2 = 0; } /* Found required data */ if (!r1_wrap && r2_wrap) return arq1; else if (!r2_wrap && r1_wrap) return arq2; else if (r1_wrap && r2_wrap) { /* both behind the head */ if (s1 <= s2) return arq1; else return arq2; } /* Both requests in front of the head */ if (d1 < d2) return arq1; else if (d2 < d1) return arq2; else { if (s1 >= s2) return arq1; else return arq2; } } /* * as_find_next_arq finds the next request after @prev in elevator order. * this with as_choose_req form the basis for how the scheduler chooses * what request to process next. Anticipation works on top of this. */ static struct as_rq *as_find_next_arq(struct as_data *ad, struct as_rq *last) { const int data_dir = last->is_sync; struct as_rq *ret; struct rb_node *rbnext = rb_next(&last->rb_node); struct rb_node *rbprev = rb_prev(&last->rb_node); struct as_rq *arq_next, *arq_prev; BUG_ON(!ON_RB(&last->rb_node)); if (rbprev) arq_prev = rb_entry_arq(rbprev); else arq_prev = NULL; if (rbnext) arq_next = rb_entry_arq(rbnext); else { arq_next = as_find_first_arq(ad, data_dir); if (arq_next == last) arq_next = NULL; } ret = as_choose_req(ad, arq_next, arq_prev); return ret; } /* * anticipatory scheduling functions follow */ /* * as_antic_expired tells us when we have anticipated too long. * The funny "absolute difference" math on the elapsed time is to handle * jiffy wraps, and disks which have been idle for 0x80000000 jiffies. */ static int as_antic_expired(struct as_data *ad) { long delta_jif; delta_jif = jiffies - ad->antic_start; if (unlikely(delta_jif < 0)) delta_jif = -delta_jif; if (delta_jif < ad->antic_expire) return 0; return 1; } /* * as_antic_waitnext starts anticipating that a nice request will soon be * submitted. See also as_antic_waitreq */ static void as_antic_waitnext(struct as_data *ad) { unsigned long timeout; BUG_ON(ad->antic_status != ANTIC_OFF && ad->antic_status != ANTIC_WAIT_REQ); timeout = ad->antic_start + ad->antic_expire; mod_timer(&ad->antic_timer, timeout); ad->antic_status = ANTIC_WAIT_NEXT; } /* * as_antic_waitreq starts anticipating. We don't start timing the anticipation * until the request that we're anticipating on has finished. This means we * are timing from when the candidate process wakes up hopefully. */ static void as_antic_waitreq(struct as_data *ad) { BUG_ON(ad->antic_status == ANTIC_FINISHED); if (ad->antic_status == ANTIC_OFF) { if (!ad->io_context || ad->ioc_finished) as_antic_waitnext(ad); else ad->antic_status = ANTIC_WAIT_REQ; } } /* * This is called directly by the functions in this file to stop anticipation. * We kill the timer and schedule a call to the request_fn asap. */ static void as_antic_stop(struct as_data *ad) { int status = ad->antic_status; if (status == ANTIC_WAIT_REQ || status == ANTIC_WAIT_NEXT) { if (status == ANTIC_WAIT_NEXT) del_timer(&ad->antic_timer); ad->antic_status = ANTIC_FINISHED; /* see as_work_handler */ kblockd_schedule_work(&ad->antic_work); } } /* * as_antic_timeout is the timer function set by as_antic_waitnext. */ static void as_antic_timeout(unsigned long data) { struct request_queue *q = (struct request_queue *)data; struct as_data *ad = q->elevator->elevator_data; unsigned long flags; spin_lock_irqsave(q->queue_lock, flags); if (ad->antic_status == ANTIC_WAIT_REQ || ad->antic_status == ANTIC_WAIT_NEXT) { struct as_io_context *aic = ad->io_context->aic; ad->antic_status = ANTIC_FINISHED; kblockd_schedule_work(&ad->antic_work); if (aic->ttime_samples == 0) { /* process anticipated on has exited or timed out*/ ad->exit_prob = (7*ad->exit_prob + 256)/8; } if (!test_bit(AS_TASK_RUNNING, &aic->state)) { /* process not "saved" by a cooperating request */ ad->exit_no_coop = (7*ad->exit_no_coop + 256)/8; } } spin_unlock_irqrestore(q->queue_lock, flags); } static void as_update_thinktime(struct as_data *ad, struct as_io_context *aic, unsigned long ttime) { /* fixed point: 1.0 == 1<<8 */ if (aic->ttime_samples == 0) { ad->new_ttime_total = (7*ad->new_ttime_total + 256*ttime) / 8; ad->new_ttime_mean = ad->new_ttime_total / 256; ad->exit_prob = (7*ad->exit_prob)/8; } aic->ttime_samples = (7*aic->ttime_samples + 256) / 8; aic->ttime_total = (7*aic->ttime_total + 256*ttime) / 8; aic->ttime_mean = (aic->ttime_total + 128) / aic->ttime_samples; } static void as_update_seekdist(struct as_data *ad, struct as_io_context *aic, sector_t sdist) { u64 total; if (aic->seek_samples == 0) { ad->new_seek_total = (7*ad->new_seek_total + 256*(u64)sdist)/8; ad->new_seek_mean = ad->new_seek_total / 256; } /* * Don't allow the seek distance to get too large from the * odd fragment, pagein, etc */ if (aic->seek_samples <= 60) /* second&third seek */ sdist = min(sdist, (aic->seek_mean * 4) + 2*1024*1024); else sdist = min(sdist, (aic->seek_mean * 4) + 2*1024*64); aic->seek_samples = (7*aic->seek_samples + 256) / 8; aic->seek_total = (7*aic->seek_total + (u64)256*sdist) / 8; total = aic->seek_total + (aic->seek_samples/2); do_div(total, aic->seek_samples); aic->seek_mean = (sector_t)total; } /* * as_update_iohist keeps a decaying histogram of IO thinktimes, and * updates @aic->ttime_mean based on that. It is called when a new * request is queued. */ static void as_update_iohist(struct as_data *ad, struct as_io_context *aic, struct request *rq) { struct as_rq *arq = RQ_DATA(rq); int data_dir = arq->is_sync; unsigned long thinktime = 0; sector_t seek_dist; if (aic == NULL) return; if (data_dir == REQ_SYNC) { unsigned long in_flight = atomic_read(&aic->nr_queued) + atomic_read(&aic->nr_dispatched); spin_lock(&aic->lock); if (test_bit(AS_TASK_IORUNNING, &aic->state) || test_bit(AS_TASK_IOSTARTED, &aic->state)) { /* Calculate read -> read thinktime */ if (test_bit(AS_TASK_IORUNNING, &aic->state) && in_flight == 0) { thinktime = jiffies - aic->last_end_request; thinktime = min(thinktime, MAX_THINKTIME-1); } as_update_thinktime(ad, aic, thinktime); /* Calculate read -> read seek distance */ if (aic->last_request_pos < rq->sector) seek_dist = rq->sector - aic->last_request_pos; else seek_dist = aic->last_request_pos - rq->sector; as_update_seekdist(ad, aic, seek_dist); } aic->last_request_pos = rq->sector + rq->nr_sectors; set_bit(AS_TASK_IOSTARTED, &aic->state); spin_unlock(&aic->lock); } } /* * as_close_req decides if one request is considered "close" to the * previous one issued. */ static int as_close_req(struct as_data *ad, struct as_io_context *aic, struct as_rq *arq) { unsigned long delay; /* milliseconds */ sector_t last = ad->last_sector[ad->batch_data_dir]; sector_t next = arq->request->sector; sector_t delta; /* acceptable close offset (in sectors) */ sector_t s; if (ad->antic_status == ANTIC_OFF || !ad->ioc_finished) delay = 0; else delay = ((jiffies - ad->antic_start) * 1000) / HZ; if (delay == 0) delta = 8192; else if (delay <= 20 && delay <= ad->antic_expire) delta = 8192 << delay; else return 1; if ((last <= next + (delta>>1)) && (next <= last + delta)) return 1; if (last < next) s = next - last; else s = last - next; if (aic->seek_samples == 0) { /* * Process has just started IO. Use past statistics to * gauge success possibility */ if (ad->new_seek_mean > s) { /* this request is better than what we're expecting */ return 1; } } else { if (aic->seek_mean > s) { /* this request is better than what we're expecting */ return 1; } } return 0; } /* * as_can_break_anticipation returns true if we have been anticipating this * request. * * It also returns true if the process against which we are anticipating * submits a write - that's presumably an fsync, O_SYNC write, etc. We want to * dispatch it ASAP, because we know that application will not be submitting * any new reads. * * If the task which has submitted the request has exited, break anticipation. * * If this task has queued some other IO, do not enter enticipation. */ static int as_can_break_anticipation(struct as_data *ad, struct as_rq *arq) { struct io_context *ioc; struct as_io_context *aic; ioc = ad->io_context; BUG_ON(!ioc); if (arq && ioc == arq->io_context) { /* request from same process */ return 1; } if (ad->ioc_finished && as_antic_expired(ad)) { /* * In this situation status should really be FINISHED, * however the timer hasn't had the chance to run yet. */ return 1; } aic = ioc->aic; if (!aic) return 0; if (atomic_read(&aic->nr_queued) > 0) { /* process has more requests queued */ return 1; } if (atomic_read(&aic->nr_dispatched) > 0) { /* process has more requests dispatched */ return 1; } if (arq && arq->is_sync == REQ_SYNC && as_close_req(ad, aic, arq)) { /* * Found a close request that is not one of ours. * * This makes close requests from another process update * our IO history. Is generally useful when there are * two or more cooperating processes working in the same * area. */ if (!test_bit(AS_TASK_RUNNING, &aic->state)) { if (aic->ttime_samples == 0) ad->exit_prob = (7*ad->exit_prob + 256)/8; ad->exit_no_coop = (7*ad->exit_no_coop)/8; } as_update_iohist(ad, aic, arq->request); return 1; } if (!test_bit(AS_TASK_RUNNING, &aic->state)) { /* process anticipated on has exited */ if (aic->ttime_samples == 0) ad->exit_prob = (7*ad->exit_prob + 256)/8; if (ad->exit_no_coop > 128) return 1; } if (aic->ttime_samples == 0) { if (ad->new_ttime_mean > ad->antic_expire) return 1; if (ad->exit_prob * ad->exit_no_coop > 128*256) return 1; } else if (aic->ttime_mean > ad->antic_expire) { /* the process thinks too much between requests */ return 1; } return 0; } /* * as_can_anticipate indicates weather we should either run arq * or keep anticipating a better request. */ static int as_can_anticipate(struct as_data *ad, struct as_rq *arq) { if (!ad->io_context) /* * Last request submitted was a write */ return 0; if (ad->antic_status == ANTIC_FINISHED) /* * Don't restart if we have just finished. Run the next request */ return 0; if (as_can_break_anticipation(ad, arq)) /* * This request is a good candidate. Don't keep anticipating, * run it. */ return 0; /* * OK from here, we haven't finished, and don't have a decent request! * Status is either ANTIC_OFF so start waiting, * ANTIC_WAIT_REQ so continue waiting for request to finish * or ANTIC_WAIT_NEXT so continue waiting for an acceptable request. */ return 1; } /* * as_update_arq must be called whenever a request (arq) is added to * the sort_list. This function keeps caches up to date, and checks if the * request might be one we are "anticipating" */ static void as_update_arq(struct as_data *ad, struct as_rq *arq) { const int data_dir = arq->is_sync; /* keep the next_arq cache up to date */ ad->next_arq[data_dir] = as_choose_req(ad, arq, ad->next_arq[data_dir]); /* * have we been anticipating this request? * or does it come from the same process as the one we are anticipating * for? */ if (ad->antic_status == ANTIC_WAIT_REQ || ad->antic_status == ANTIC_WAIT_NEXT) { if (as_can_break_anticipation(ad, arq)) as_antic_stop(ad); } } /* * Gathers timings and resizes the write batch automatically */ static void update_write_batch(struct as_data *ad) { unsigned long batch = ad->batch_expire[REQ_ASYNC]; long write_time; write_time = (jiffies - ad->current_batch_expires) + batch; if (write_time < 0) write_time = 0; if (write_time > batch && !ad->write_batch_idled) { if (write_time > batch * 3) ad->write_batch_count /= 2; else ad->write_batch_count--; } else if (write_time < batch && ad->current_write_count == 0) { if (batch > write_time * 3) ad->write_batch_count *= 2; else ad->write_batch_count++; } if (ad->write_batch_count < 1) ad->write_batch_count = 1; } /* * as_completed_request is to be called when a request has completed and * returned something to the requesting process, be it an error or data. */ static void as_completed_request(request_queue_t *q, struct request *rq) { struct as_data *ad = q->elevator->elevator_data; struct as_rq *arq = RQ_DATA(rq); WARN_ON(!list_empty(&rq->queuelist)); if (arq->state != AS_RQ_REMOVED) { printk("arq->state %d\n", arq->state); WARN_ON(1); goto out; } if (ad->changed_batch && ad->nr_dispatched == 1) { kblockd_schedule_work(&ad->antic_work); ad->changed_batch = 0; if (ad->batch_data_dir == REQ_SYNC) ad->new_batch = 1; } WARN_ON(ad->nr_dispatched == 0); ad->nr_dispatched--; /* * Start counting the batch from when a request of that direction is * actually serviced. This should help devices with big TCQ windows * and writeback caches */ if (ad->new_batch && ad->batch_data_dir == arq->is_sync) { update_write_batch(ad); ad->current_batch_expires = jiffies + ad->batch_expire[REQ_SYNC]; ad->new_batch = 0; } if (ad->io_context == arq->io_context && ad->io_context) { ad->antic_start = jiffies; ad->ioc_finished = 1; if (ad->antic_status == ANTIC_WAIT_REQ) { /* * We were waiting on this request, now anticipate * the next one */ as_antic_waitnext(ad); } } as_put_io_context(arq); out: arq->state = AS_RQ_POSTSCHED; } /* * as_remove_queued_request removes a request from the pre dispatch queue * without updating refcounts. It is expected the caller will drop the * reference unless it replaces the request at somepart of the elevator * (ie. the dispatch queue) */ static void as_remove_queued_request(request_queue_t *q, struct request *rq) { struct as_rq *arq = RQ_DATA(rq); const int data_dir = arq->is_sync; struct as_data *ad = q->elevator->elevator_data; WARN_ON(arq->state != AS_RQ_QUEUED); if (arq->io_context && arq->io_context->aic) { BUG_ON(!atomic_read(&arq->io_context->aic->nr_queued)); atomic_dec(&arq->io_context->aic->nr_queued); } /* * Update the "next_arq" cache if we are about to remove its * entry */ if (ad->next_arq[data_dir] == arq) ad->next_arq[data_dir] = as_find_next_arq(ad, arq); list_del_init(&arq->fifo); as_del_arq_hash(arq); as_del_arq_rb(ad, arq); } /* * as_fifo_expired returns 0 if there are no expired reads on the fifo, * 1 otherwise. It is ratelimited so that we only perform the check once per * `fifo_expire' interval. Otherwise a large number of expired requests * would create a hopeless seekstorm. * * See as_antic_expired comment. */ static int as_fifo_expired(struct as_data *ad, int adir) { struct as_rq *arq; long delta_jif; delta_jif = jiffies - ad->last_check_fifo[adir]; if (unlikely(delta_jif < 0)) delta_jif = -delta_jif; if (delta_jif < ad->fifo_expire[adir]) return 0; ad->last_check_fifo[adir] = jiffies; if (list_empty(&ad->fifo_list[adir])) return 0; arq = list_entry_fifo(ad->fifo_list[adir].next); return time_after(jiffies, arq->expires); } /* * as_batch_expired returns true if the current batch has expired. A batch * is a set of reads or a set of writes. */ static inline int as_batch_expired(struct as_data *ad) { if (ad->changed_batch || ad->new_batch) return 0; if (ad->batch_data_dir == REQ_SYNC) /* TODO! add a check so a complete fifo gets written? */ return time_after(jiffies, ad->current_batch_expires); return time_after(jiffies, ad->current_batch_expires) || ad->current_write_count == 0; } /* * move an entry to dispatch queue */ static void as_move_to_dispatch(struct as_data *ad, struct as_rq *arq) { struct request *rq = arq->request; const int data_dir = arq->is_sync; BUG_ON(!ON_RB(&arq->rb_node)); as_antic_stop(ad); ad->antic_status = ANTIC_OFF; /* * This has to be set in order to be correctly updated by * as_find_next_arq */ ad->last_sector[data_dir] = rq->sector + rq->nr_sectors; if (data_dir == REQ_SYNC) { /* In case we have to anticipate after this */ copy_io_context(&ad->io_context, &arq->io_context); } else { if (ad->io_context) { put_io_context(ad->io_context); ad->io_context = NULL; } if (ad->current_write_count != 0) ad->current_write_count--; } ad->ioc_finished = 0; ad->next_arq[data_dir] = as_find_next_arq(ad, arq); /* * take it off the sort and fifo list, add to dispatch queue */ as_remove_queued_request(ad->q, rq); WARN_ON(arq->state != AS_RQ_QUEUED); elv_dispatch_sort(ad->q, rq); arq->state = AS_RQ_DISPATCHED; if (arq->io_context && arq->io_context->aic) atomic_inc(&arq->io_context->aic->nr_dispatched); ad->nr_dispatched++; } /* * as_dispatch_request selects the best request according to * read/write expire, batch expire, etc, and moves it to the dispatch * queue. Returns 1 if a request was found, 0 otherwise. */ static int as_dispatch_request(request_queue_t *q, int force) { struct as_data *ad = q->elevator->elevator_data; struct as_rq *arq; const int reads = !list_empty(&ad->fifo_list[REQ_SYNC]); const int writes = !list_empty(&ad->fifo_list[REQ_ASYNC]); if (unlikely(force)) { /* * Forced dispatch, accounting is useless. Reset * accounting states and dump fifo_lists. Note that * batch_data_dir is reset to REQ_SYNC to avoid * screwing write batch accounting as write batch * accounting occurs on W->R transition. */ int dispatched = 0; ad->batch_data_dir = REQ_SYNC; ad->changed_batch = 0; ad->new_batch = 0; while (ad->next_arq[REQ_SYNC]) { as_move_to_dispatch(ad, ad->next_arq[REQ_SYNC]); dispatched++; } ad->last_check_fifo[REQ_SYNC] = jiffies; while (ad->next_arq[REQ_ASYNC]) { as_move_to_dispatch(ad, ad->next_arq[REQ_ASYNC]); dispatched++; } ad->last_check_fifo[REQ_ASYNC] = jiffies; return dispatched; } /* Signal that the write batch was uncontended, so we can't time it */ if (ad->batch_data_dir == REQ_ASYNC && !reads) { if (ad->current_write_count == 0 || !writes) ad->write_batch_idled = 1; } if (!(reads || writes) || ad->antic_status == ANTIC_WAIT_REQ || ad->antic_status == ANTIC_WAIT_NEXT || ad->changed_batch) return 0; if (!(reads && writes && as_batch_expired(ad))) { /* * batch is still running or no reads or no writes */ arq = ad->next_arq[ad->batch_data_dir]; if (ad->batch_data_dir == REQ_SYNC && ad->antic_expire) { if (as_fifo_expired(ad, REQ_SYNC)) goto fifo_expired; if (as_can_anticipate(ad, arq)) { as_antic_waitreq(ad); return 0; } } if (arq) { /* we have a "next request" */ if (reads && !writes) ad->current_batch_expires = jiffies + ad->batch_expire[REQ_SYNC]; goto dispatch_request; } } /* * at this point we are not running a batch. select the appropriate * data direction (read / write) */ if (reads) { BUG_ON(RB_EMPTY(&ad->sort_list[REQ_SYNC])); if (writes && ad->batch_data_dir == REQ_SYNC) /* * Last batch was a read, switch to writes */ goto dispatch_writes; if (ad->batch_data_dir == REQ_ASYNC) { WARN_ON(ad->new_batch); ad->changed_batch = 1; } ad->batch_data_dir = REQ_SYNC; arq = list_entry_fifo(ad->fifo_list[ad->batch_data_dir].next); ad->last_check_fifo[ad->batch_data_dir] = jiffies; goto dispatch_request; } /* * the last batch was a read */ if (writes) { dispatch_writes: BUG_ON(RB_EMPTY(&ad->sort_list[REQ_ASYNC])); if (ad->batch_data_dir == REQ_SYNC) { ad->changed_batch = 1; /* * new_batch might be 1 when the queue runs out of * reads. A subsequent submission of a write might * cause a change of batch before the read is finished. */ ad->new_batch = 0; } ad->batch_data_dir = REQ_ASYNC; ad->current_write_count = ad->write_batch_count; ad->write_batch_idled = 0; arq = ad->next_arq[ad->batch_data_dir]; goto dispatch_request; } BUG(); return 0; dispatch_request: /* * If a request has expired, service it. */ if (as_fifo_expired(ad, ad->batch_data_dir)) { fifo_expired: arq = list_entry_fifo(ad->fifo_list[ad->batch_data_dir].next); BUG_ON(arq == NULL); } if (ad->changed_batch) { WARN_ON(ad->new_batch); if (ad->nr_dispatched) return 0; if (ad->batch_data_dir == REQ_ASYNC) ad->current_batch_expires = jiffies + ad->batch_expire[REQ_ASYNC]; else ad->new_batch = 1; ad->changed_batch = 0; } /* * arq is the selected appropriate request. */ as_move_to_dispatch(ad, arq); return 1; } /* * add arq to rbtree and fifo */ static void as_add_request(request_queue_t *q, struct request *rq) { struct as_data *ad = q->elevator->elevator_data; struct as_rq *arq = RQ_DATA(rq); int data_dir; arq->state = AS_RQ_NEW; if (rq_data_dir(arq->request) == READ || current->flags&PF_SYNCWRITE) arq->is_sync = 1; else arq->is_sync = 0; data_dir = arq->is_sync; arq->io_context = as_get_io_context(); if (arq->io_context) { as_update_iohist(ad, arq->io_context->aic, arq->request); atomic_inc(&arq->io_context->aic->nr_queued); } as_add_arq_rb(ad, arq); if (rq_mergeable(arq->request)) as_add_arq_hash(ad, arq); /* * set expire time (only used for reads) and add to fifo list */ arq->expires = jiffies + ad->fifo_expire[data_dir]; list_add_tail(&arq->fifo, &ad->fifo_list[data_dir]); as_update_arq(ad, arq); /* keep state machine up to date */ arq->state = AS_RQ_QUEUED; } static void as_activate_request(request_queue_t *q, struct request *rq) { struct as_rq *arq = RQ_DATA(rq); WARN_ON(arq->state != AS_RQ_DISPATCHED); arq->state = AS_RQ_REMOVED; if (arq->io_context && arq->io_context->aic) atomic_dec(&arq->io_context->aic->nr_dispatched); } static void as_deactivate_request(request_queue_t *q, struct request *rq) { struct as_rq *arq = RQ_DATA(rq); WARN_ON(arq->state != AS_RQ_REMOVED); arq->state = AS_RQ_DISPATCHED; if (arq->io_context && arq->io_context->aic) atomic_inc(&arq->io_context->aic->nr_dispatched); } /* * as_queue_empty tells us if there are requests left in the device. It may * not be the case that a driver can get the next request even if the queue * is not empty - it is used in the block layer to check for plugging and * merging opportunities */ static int as_queue_empty(request_queue_t *q) { struct as_data *ad = q->elevator->elevator_data; return list_empty(&ad->fifo_list[REQ_ASYNC]) && list_empty(&ad->fifo_list[REQ_SYNC]); } static struct request *as_former_request(request_queue_t *q, struct request *rq) { struct as_rq *arq = RQ_DATA(rq); struct rb_node *rbprev = rb_prev(&arq->rb_node); struct request *ret = NULL; if (rbprev) ret = rb_entry_arq(rbprev)->request; return ret; } static struct request *as_latter_request(request_queue_t *q, struct request *rq) { struct as_rq *arq = RQ_DATA(rq); struct rb_node *rbnext = rb_next(&arq->rb_node); struct request *ret = NULL; if (rbnext) ret = rb_entry_arq(rbnext)->request; return ret; } static int as_merge(request_queue_t *q, struct request **req, struct bio *bio) { struct as_data *ad = q->elevator->elevator_data; sector_t rb_key = bio->bi_sector + bio_sectors(bio); struct request *__rq; int ret; /* * see if the merge hash can satisfy a back merge */ __rq = as_find_arq_hash(ad, bio->bi_sector); if (__rq) { BUG_ON(__rq->sector + __rq->nr_sectors != bio->bi_sector); if (elv_rq_merge_ok(__rq, bio)) { ret = ELEVATOR_BACK_MERGE; goto out; } } /* * check for front merge */ __rq = as_find_arq_rb(ad, rb_key, bio_data_dir(bio)); if (__rq) { BUG_ON(rb_key != rq_rb_key(__rq)); if (elv_rq_merge_ok(__rq, bio)) { ret = ELEVATOR_FRONT_MERGE; goto out; } } return ELEVATOR_NO_MERGE; out: if (ret) { if (rq_mergeable(__rq)) as_hot_arq_hash(ad, RQ_DATA(__rq)); } *req = __rq; return ret; } static void as_merged_request(request_queue_t *q, struct request *req) { struct as_data *ad = q->elevator->elevator_data; struct as_rq *arq = RQ_DATA(req); /* * hash always needs to be repositioned, key is end sector */ as_del_arq_hash(arq); as_add_arq_hash(ad, arq); /* * if the merge was a front merge, we need to reposition request */ if (rq_rb_key(req) != arq->rb_key) { as_del_arq_rb(ad, arq); as_add_arq_rb(ad, arq); /* * Note! At this stage of this and the next function, our next * request may not be optimal - eg the request may have "grown" * behind the disk head. We currently don't bother adjusting. */ } } static void as_merged_requests(request_queue_t *q, struct request *req, struct request *next) { struct as_data *ad = q->elevator->elevator_data; struct as_rq *arq = RQ_DATA(req); struct as_rq *anext = RQ_DATA(next); BUG_ON(!arq); BUG_ON(!anext); /* * reposition arq (this is the merged request) in hash, and in rbtree * in case of a front merge */ as_del_arq_hash(arq); as_add_arq_hash(ad, arq); if (rq_rb_key(req) != arq->rb_key) { as_del_arq_rb(ad, arq); as_add_arq_rb(ad, arq); } /* * if anext expires before arq, assign its expire time to arq * and move into anext position (anext will be deleted) in fifo */ if (!list_empty(&arq->fifo) && !list_empty(&anext->fifo)) { if (time_before(anext->expires, arq->expires)) { list_move(&arq->fifo, &anext->fifo); arq->expires = anext->expires; /* * Don't copy here but swap, because when anext is * removed below, it must contain the unused context */ swap_io_context(&arq->io_context, &anext->io_context); } } /* * kill knowledge of next, this one is a goner */ as_remove_queued_request(q, next); as_put_io_context(anext); anext->state = AS_RQ_MERGED; } /* * This is executed in a "deferred" process context, by kblockd. It calls the * driver's request_fn so the driver can submit that request. * * IMPORTANT! This guy will reenter the elevator, so set up all queue global * state before calling, and don't rely on any state over calls. * * FIXME! dispatch queue is not a queue at all! */ static void as_work_handler(void *data) { struct request_queue *q = data; unsigned long flags; spin_lock_irqsave(q->queue_lock, flags); if (!as_queue_empty(q)) q->request_fn(q); spin_unlock_irqrestore(q->queue_lock, flags); } static void as_put_request(request_queue_t *q, struct request *rq) { struct as_data *ad = q->elevator->elevator_data; struct as_rq *arq = RQ_DATA(rq); if (!arq) { WARN_ON(1); return; } if (unlikely(arq->state != AS_RQ_POSTSCHED && arq->state != AS_RQ_PRESCHED && arq->state != AS_RQ_MERGED)) { printk("arq->state %d\n", arq->state); WARN_ON(1); } mempool_free(arq, ad->arq_pool); rq->elevator_private = NULL; } static int as_set_request(request_queue_t *q, struct request *rq, struct bio *bio, gfp_t gfp_mask) { struct as_data *ad = q->elevator->elevator_data; struct as_rq *arq = mempool_alloc(ad->arq_pool, gfp_mask); if (arq) { memset(arq, 0, sizeof(*arq)); RB_CLEAR(&arq->rb_node); arq->request = rq; arq->state = AS_RQ_PRESCHED; arq->io_context = NULL; INIT_LIST_HEAD(&arq->hash); arq->on_hash = 0; INIT_LIST_HEAD(&arq->fifo); rq->elevator_private = arq; return 0; } return 1; } static int as_may_queue(request_queue_t *q, int rw, struct bio *bio) { int ret = ELV_MQUEUE_MAY; struct as_data *ad = q->elevator->elevator_data; struct io_context *ioc; if (ad->antic_status == ANTIC_WAIT_REQ || ad->antic_status == ANTIC_WAIT_NEXT) { ioc = as_get_io_context(); if (ad->io_context == ioc) ret = ELV_MQUEUE_MUST; put_io_context(ioc); } return ret; } static void as_exit_queue(elevator_t *e) { struct as_data *ad = e->elevator_data; del_timer_sync(&ad->antic_timer); kblockd_flush(); BUG_ON(!list_empty(&ad->fifo_list[REQ_SYNC])); BUG_ON(!list_empty(&ad->fifo_list[REQ_ASYNC])); mempool_destroy(ad->arq_pool); put_io_context(ad->io_context); kfree(ad->hash); kfree(ad); } /* * initialize elevator private data (as_data), and alloc a arq for * each request on the free lists */ static void *as_init_queue(request_queue_t *q, elevator_t *e) { struct as_data *ad; int i; if (!arq_pool) return NULL; ad = kmalloc_node(sizeof(*ad), GFP_KERNEL, q->node); if (!ad) return NULL; memset(ad, 0, sizeof(*ad)); ad->q = q; /* Identify what queue the data belongs to */ ad->hash = kmalloc_node(sizeof(struct list_head)*AS_HASH_ENTRIES, GFP_KERNEL, q->node); if (!ad->hash) { kfree(ad); return NULL; } ad->arq_pool = mempool_create_node(BLKDEV_MIN_RQ, mempool_alloc_slab, mempool_free_slab, arq_pool, q->node); if (!ad->arq_pool) { kfree(ad->hash); kfree(ad); return NULL; } /* anticipatory scheduling helpers */ ad->antic_timer.function = as_antic_timeout; ad->antic_timer.data = (unsigned long)q; init_timer(&ad->antic_timer); INIT_WORK(&ad->antic_work, as_work_handler, q); for (i = 0; i < AS_HASH_ENTRIES; i++) INIT_LIST_HEAD(&ad->hash[i]); INIT_LIST_HEAD(&ad->fifo_list[REQ_SYNC]); INIT_LIST_HEAD(&ad->fifo_list[REQ_ASYNC]); ad->sort_list[REQ_SYNC] = RB_ROOT; ad->sort_list[REQ_ASYNC] = RB_ROOT; ad->fifo_expire[REQ_SYNC] = default_read_expire; ad->fifo_expire[REQ_ASYNC] = default_write_expire; ad->antic_expire = default_antic_expire; ad->batch_expire[REQ_SYNC] = default_read_batch_expire; ad->batch_expire[REQ_ASYNC] = default_write_batch_expire; ad->current_batch_expires = jiffies + ad->batch_expire[REQ_SYNC]; ad->write_batch_count = ad->batch_expire[REQ_ASYNC] / 10; if (ad->write_batch_count < 2) ad->write_batch_count = 2; return ad; } /* * sysfs parts below */ static ssize_t as_var_show(unsigned int var, char *page) { return sprintf(page, "%d\n", var); } static ssize_t as_var_store(unsigned long *var, const char *page, size_t count) { char *p = (char *) page; *var = simple_strtoul(p, &p, 10); return count; } static ssize_t est_time_show(elevator_t *e, char *page) { struct as_data *ad = e->elevator_data; int pos = 0; pos += sprintf(page+pos, "%lu %% exit probability\n", 100*ad->exit_prob/256); pos += sprintf(page+pos, "%lu %% probability of exiting without a " "cooperating process submitting IO\n", 100*ad->exit_no_coop/256); pos += sprintf(page+pos, "%lu ms new thinktime\n", ad->new_ttime_mean); pos += sprintf(page+pos, "%llu sectors new seek distance\n", (unsigned long long)ad->new_seek_mean); return pos; } #define SHOW_FUNCTION(__FUNC, __VAR) \ static ssize_t __FUNC(elevator_t *e, char *page) \ { \ struct as_data *ad = e->elevator_data; \ return as_var_show(jiffies_to_msecs((__VAR)), (page)); \ } SHOW_FUNCTION(as_read_expire_show, ad->fifo_expire[REQ_SYNC]); SHOW_FUNCTION(as_write_expire_show, ad->fifo_expire[REQ_ASYNC]); SHOW_FUNCTION(as_antic_expire_show, ad->antic_expire); SHOW_FUNCTION(as_read_batch_expire_show, ad->batch_expire[REQ_SYNC]); SHOW_FUNCTION(as_write_batch_expire_show, ad->batch_expire[REQ_ASYNC]); #undef SHOW_FUNCTION #define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX) \ static ssize_t __FUNC(elevator_t *e, const char *page, size_t count) \ { \ struct as_data *ad = e->elevator_data; \ int ret = as_var_store(__PTR, (page), count); \ if (*(__PTR) < (MIN)) \ *(__PTR) = (MIN); \ else if (*(__PTR) > (MAX)) \ *(__PTR) = (MAX); \ *(__PTR) = msecs_to_jiffies(*(__PTR)); \ return ret; \ } STORE_FUNCTION(as_read_expire_store, &ad->fifo_expire[REQ_SYNC], 0, INT_MAX); STORE_FUNCTION(as_write_expire_store, &ad->fifo_expire[REQ_ASYNC], 0, INT_MAX); STORE_FUNCTION(as_antic_expire_store, &ad->antic_expire, 0, INT_MAX); STORE_FUNCTION(as_read_batch_expire_store, &ad->batch_expire[REQ_SYNC], 0, INT_MAX); STORE_FUNCTION(as_write_batch_expire_store, &ad->batch_expire[REQ_ASYNC], 0, INT_MAX); #undef STORE_FUNCTION #define AS_ATTR(name) \ __ATTR(name, S_IRUGO|S_IWUSR, as_##name##_show, as_##name##_store) static struct elv_fs_entry as_attrs[] = { __ATTR_RO(est_time), AS_ATTR(read_expire), AS_ATTR(write_expire), AS_ATTR(antic_expire), AS_ATTR(read_batch_expire), AS_ATTR(write_batch_expire), __ATTR_NULL }; static struct elevator_type iosched_as = { .ops = { .elevator_merge_fn = as_merge, .elevator_merged_fn = as_merged_request, .elevator_merge_req_fn = as_merged_requests, .elevator_dispatch_fn = as_dispatch_request, .elevator_add_req_fn = as_add_request, .elevator_activate_req_fn = as_activate_request, .elevator_deactivate_req_fn = as_deactivate_request, .elevator_queue_empty_fn = as_queue_empty, .elevator_completed_req_fn = as_completed_request, .elevator_former_req_fn = as_former_request, .elevator_latter_req_fn = as_latter_request, .elevator_set_req_fn = as_set_request, .elevator_put_req_fn = as_put_request, .elevator_may_queue_fn = as_may_queue, .elevator_init_fn = as_init_queue, .elevator_exit_fn = as_exit_queue, .trim = as_trim, }, .elevator_attrs = as_attrs, .elevator_name = "anticipatory", .elevator_owner = THIS_MODULE, }; static int __init as_init(void) { int ret; arq_pool = kmem_cache_create("as_arq", sizeof(struct as_rq), 0, 0, NULL, NULL); if (!arq_pool) return -ENOMEM; ret = elv_register(&iosched_as); if (!ret) { /* * don't allow AS to get unregistered, since we would have * to browse all tasks in the system and release their * as_io_context first */ __module_get(THIS_MODULE); return 0; } kmem_cache_destroy(arq_pool); return ret; } static void __exit as_exit(void) { DECLARE_COMPLETION(all_gone); elv_unregister(&iosched_as); ioc_gone = &all_gone; /* ioc_gone's update must be visible before reading ioc_count */ smp_wmb(); if (atomic_read(&ioc_count)) wait_for_completion(ioc_gone); synchronize_rcu(); kmem_cache_destroy(arq_pool); } module_init(as_init); module_exit(as_exit); MODULE_AUTHOR("Nick Piggin"); MODULE_LICENSE("GPL"); MODULE_DESCRIPTION("anticipatory IO scheduler");