/* * Block device elevator/IO-scheduler. * * Copyright (C) 2000 Andrea Arcangeli <andrea@suse.de> SuSE * * 30042000 Jens Axboe <axboe@kernel.dk> : * * Split the elevator a bit so that it is possible to choose a different * one or even write a new "plug in". There are three pieces: * - elevator_fn, inserts a new request in the queue list * - elevator_merge_fn, decides whether a new buffer can be merged with * an existing request * - elevator_dequeue_fn, called when a request is taken off the active list * * 20082000 Dave Jones <davej@suse.de> : * Removed tests for max-bomb-segments, which was breaking elvtune * when run without -bN * * Jens: * - Rework again to work with bio instead of buffer_heads * - loose bi_dev comparisons, partition handling is right now * - completely modularize elevator setup and teardown * */#include <linux/kernel.h>#include <linux/fs.h>#include <linux/blkdev.h>#include <linux/elevator.h>#include <linux/bio.h>#include <linux/module.h>#include <linux/slab.h>#include <linux/init.h>#include <linux/compiler.h>#include <linux/blktrace_api.h>#include <linux/hash.h>#include <linux/uaccess.h>#include <linux/pm_runtime.h>#include <linux/blk-cgroup.h> #include <trace/events/block.h> #include "blk.h"#include "blk-mq-sched.h"#include "blk-wbt.h" static DEFINE_SPINLOCK(elv_list_lock);static LIST_HEAD(elv_list); /* * Merge hash stuff. */#define rq_hash_key(rq) (blk_rq_pos(rq) + blk_rq_sectors(rq)) /* * Query io scheduler to see if the current process issuing bio may be * merged with rq. */static int elv_iosched_allow_bio_merge(struct request *rq, struct bio *bio){ struct request_queue *q = rq->q; struct elevator_queue *e = q->elevator; if (e->uses_mq && e->type->ops.mq.allow_merge) return e->type->ops.mq.allow_merge(q, rq, bio); else if (!e->uses_mq && e->type->ops.sq.elevator_allow_bio_merge_fn) return e->type->ops.sq.elevator_allow_bio_merge_fn(q, rq, bio); return 1;} /* * can we safely merge with this request? */bool elv_bio_merge_ok(struct request *rq, struct bio *bio){ if (!blk_rq_merge_ok(rq, bio)) return false; if (!elv_iosched_allow_bio_merge(rq, bio)) return false; return true;}EXPORT_SYMBOL(elv_bio_merge_ok); static struct elevator_type *elevator_find(const char *name){ struct elevator_type *e; list_for_each_entry(e, &elv_list, list) { if (!strcmp(e->elevator_name, name)) return e; } return NULL;} static void elevator_put(struct elevator_type *e){ module_put(e->elevator_owner);} static struct elevator_type *elevator_get(const char *name, bool try_loading){ struct elevator_type *e; spin_lock(&elv_list_lock); e = elevator_find(name); if (!e && try_loading) { spin_unlock(&elv_list_lock); request_module("%s-iosched", name); spin_lock(&elv_list_lock); e = elevator_find(name); } if (e && !try_module_get(e->elevator_owner)) e = NULL; spin_unlock(&elv_list_lock); return e;} static char chosen_elevator[ELV_NAME_MAX]; static int __init elevator_setup(char *str){ /* * Be backwards-compatible with previous kernels, so users * won't get the wrong elevator. */ strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1); return 1;} __setup("elevator=", elevator_setup); /* called during boot to load the elevator chosen by the elevator param */void __init load_default_elevator_module(void){ struct elevator_type *e; if (!chosen_elevator[0]) return; spin_lock(&elv_list_lock); e = elevator_find(chosen_elevator); spin_unlock(&elv_list_lock); if (!e) request_module("%s-iosched", chosen_elevator);} static struct kobj_type elv_ktype; struct elevator_queue *elevator_alloc(struct request_queue *q, struct elevator_type *e){ struct elevator_queue *eq; eq = kzalloc_node(sizeof(*eq), GFP_KERNEL, q->node); if (unlikely(!eq)) return NULL; eq->type = e; kobject_init(&eq->kobj, &elv_ktype); mutex_init(&eq->sysfs_lock); hash_init(eq->hash); eq->uses_mq = e->uses_mq; return eq;}EXPORT_SYMBOL(elevator_alloc); static void elevator_release(struct kobject *kobj){ struct elevator_queue *e; e = container_of(kobj, struct elevator_queue, kobj); elevator_put(e->type); kfree(e);} int elevator_init(struct request_queue *q, char *name){ struct elevator_type *e = NULL; int err; /* * q->sysfs_lock must be held to provide mutual exclusion between * elevator_switch() and here. */ lockdep_assert_held(&q->sysfs_lock); if (unlikely(q->elevator)) return 0; INIT_LIST_HEAD(&q->queue_head); q->last_merge = NULL; q->end_sector = 0; q->boundary_rq = NULL; if (name) { e = elevator_get(name, true); if (!e) return -EINVAL; } /* * Use the default elevator specified by config boot param for * non-mq devices, or by config option. Don't try to load modules * as we could be running off async and request_module() isn't * allowed from async. */ if (!e && !q->mq_ops && *chosen_elevator) { e = elevator_get(chosen_elevator, false); if (!e) printk(KERN_ERR "I/O scheduler %s not found\n", chosen_elevator); } if (!e) { /* * For blk-mq devices, we default to using mq-deadline, * if available, for single queue devices. If deadline * isn't available OR we have multiple queues, default * to "none". */ if (q->mq_ops) { if (q->nr_hw_queues == 1) e = elevator_get("mq-deadline", false); if (!e) return 0; } else e = elevator_get(CONFIG_DEFAULT_IOSCHED, false); if (!e) { printk(KERN_ERR "Default I/O scheduler not found. " \ "Using noop.\n"); e = elevator_get("noop", false); } } if (e->uses_mq) err = blk_mq_init_sched(q, e); else err = e->ops.sq.elevator_init_fn(q, e); if (err) elevator_put(e); return err;}EXPORT_SYMBOL(elevator_init); void elevator_exit(struct request_queue *q, struct elevator_queue *e){ mutex_lock(&e->sysfs_lock); if (e->uses_mq && e->type->ops.mq.exit_sched) blk_mq_exit_sched(q, e); else if (!e->uses_mq && e->type->ops.sq.elevator_exit_fn) e->type->ops.sq.elevator_exit_fn(e); mutex_unlock(&e->sysfs_lock); kobject_put(&e->kobj);}EXPORT_SYMBOL(elevator_exit); static inline void __elv_rqhash_del(struct request *rq){ hash_del(&rq->hash); rq->rq_flags &= ~RQF_HASHED;} void elv_rqhash_del(struct request_queue *q, struct request *rq){ if (ELV_ON_HASH(rq)) __elv_rqhash_del(rq);}EXPORT_SYMBOL_GPL(elv_rqhash_del); void elv_rqhash_add(struct request_queue *q, struct request *rq){ struct elevator_queue *e = q->elevator; BUG_ON(ELV_ON_HASH(rq)); hash_add(e->hash, &rq->hash, rq_hash_key(rq)); rq->rq_flags |= RQF_HASHED;}EXPORT_SYMBOL_GPL(elv_rqhash_add); void elv_rqhash_reposition(struct request_queue *q, struct request *rq){ __elv_rqhash_del(rq); elv_rqhash_add(q, rq);} struct request *elv_rqhash_find(struct request_queue *q, sector_t offset){ struct elevator_queue *e = q->elevator; struct hlist_node *next; struct request *rq; hash_for_each_possible_safe(e->hash, rq, next, hash, offset) { BUG_ON(!ELV_ON_HASH(rq)); if (unlikely(!rq_mergeable(rq))) { __elv_rqhash_del(rq); continue; } if (rq_hash_key(rq) == offset) return rq; } return NULL;} /* * RB-tree support functions for inserting/lookup/removal of requests * in a sorted RB tree. */void elv_rb_add(struct rb_root *root, struct request *rq){ struct rb_node **p = &root->rb_node; struct rb_node *parent = NULL; struct request *__rq; while (*p) { parent = *p; __rq = rb_entry(parent, struct request, rb_node); if (blk_rq_pos(rq) < blk_rq_pos(__rq)) p = &(*p)->rb_left; else if (blk_rq_pos(rq) >= blk_rq_pos(__rq)) p = &(*p)->rb_right; } rb_link_node(&rq->rb_node, parent, p); rb_insert_color(&rq->rb_node, root);}EXPORT_SYMBOL(elv_rb_add); void elv_rb_del(struct rb_root *root, struct request *rq){ BUG_ON(RB_EMPTY_NODE(&rq->rb_node)); rb_erase(&rq->rb_node, root); RB_CLEAR_NODE(&rq->rb_node);}EXPORT_SYMBOL(elv_rb_del); struct request *elv_rb_find(struct rb_root *root, sector_t sector){ struct rb_node *n = root->rb_node; struct request *rq; while (n) { rq = rb_entry(n, struct request, rb_node); if (sector < blk_rq_pos(rq)) n = n->rb_left; else if (sector > blk_rq_pos(rq)) n = n->rb_right; else return rq; } return NULL;}EXPORT_SYMBOL(elv_rb_find); /* * Insert rq into dispatch queue of q. Queue lock must be held on * entry. rq is sort instead into the dispatch queue. To be used by * specific elevators. */void elv_dispatch_sort(struct request_queue *q, struct request *rq){ sector_t boundary; struct list_head *entry; if (q->last_merge == rq) q->last_merge = NULL; elv_rqhash_del(q, rq); q->nr_sorted--; boundary = q->end_sector; list_for_each_prev(entry, &q->queue_head) { struct request *pos = list_entry_rq(entry); if (req_op(rq) != req_op(pos)) break; if (rq_data_dir(rq) != rq_data_dir(pos)) break; if (pos->rq_flags & (RQF_STARTED | RQF_SOFTBARRIER)) break; if (blk_rq_pos(rq) >= boundary) { if (blk_rq_pos(pos) < boundary) continue; } else { if (blk_rq_pos(pos) >= boundary) break; } if (blk_rq_pos(rq) >= blk_rq_pos(pos)) break; } list_add(&rq->queuelist, entry);}EXPORT_SYMBOL(elv_dispatch_sort); /* * Insert rq into dispatch queue of q. Queue lock must be held on * entry. rq is added to the back of the dispatch queue. To be used by * specific elevators. */void elv_dispatch_add_tail(struct request_queue *q, struct request *rq){ if (q->last_merge == rq) q->last_merge = NULL; elv_rqhash_del(q, rq); q->nr_sorted--; q->end_sector = rq_end_sector(rq); q->boundary_rq = rq; list_add_tail(&rq->queuelist, &q->queue_head);}EXPORT_SYMBOL(elv_dispatch_add_tail); enum elv_merge elv_merge(struct request_queue *q, struct request **req, struct bio *bio){ struct elevator_queue *e = q->elevator; struct request *__rq; /* * Levels of merges: * nomerges: No merges at all attempted * noxmerges: Only simple one-hit cache try * merges: All merge tries attempted */ if (blk_queue_nomerges(q) || !bio_mergeable(bio)) return ELEVATOR_NO_MERGE; /* * First try one-hit cache. */ if (q->last_merge && elv_bio_merge_ok(q->last_merge, bio)) { enum elv_merge ret = blk_try_merge(q->last_merge, bio); if (ret != ELEVATOR_NO_MERGE) { *req = q->last_merge; return ret; } } if (blk_queue_noxmerges(q)) return ELEVATOR_NO_MERGE; /* * See if our hash lookup can find a potential backmerge. */ __rq = elv_rqhash_find(q, bio->bi_iter.bi_sector); if (__rq && elv_bio_merge_ok(__rq, bio)) { *req = __rq; return ELEVATOR_BACK_MERGE; } if (e->uses_mq && e->type->ops.mq.request_merge) return e->type->ops.mq.request_merge(q, req, bio); else if (!e->uses_mq && e->type->ops.sq.elevator_merge_fn) return e->type->ops.sq.elevator_merge_fn(q, req, bio); return ELEVATOR_NO_MERGE;} /* * Attempt to do an insertion back merge. Only check for the case where * we can append 'rq' to an existing request, so we can throw 'rq' away * afterwards. * * Returns true if we merged, false otherwise */bool elv_attempt_insert_merge(struct request_queue *q, struct request *rq){ struct request *__rq; bool ret; if (blk_queue_nomerges(q)) return false; /* * First try one-hit cache. */ if (q->last_merge && blk_attempt_req_merge(q, q->last_merge, rq)) return true;Lines 1–500 of 1167. Load more
/* * Block device elevator/IO-scheduler. * * Copyright (C) 2000 Andrea Arcangeli <andrea@suse.de> SuSE * * 30042000 Jens Axboe <axboe@kernel.dk> : * * Split the elevator a bit so that it is possible to choose a different * one or even write a new "plug in". There are three pieces: * - elevator_fn, inserts a new request in the queue list * - elevator_merge_fn, decides whether a new buffer can be merged with * an existing request * - elevator_dequeue_fn, called when a request is taken off the active list * * 20082000 Dave Jones <davej@suse.de> : * Removed tests for max-bomb-segments, which was breaking elvtune * when run without -bN * * Jens: * - Rework again to work with bio instead of buffer_heads * - loose bi_dev comparisons, partition handling is right now * - completely modularize elevator setup and teardown * */ #include <linux/kernel.h> #include <linux/fs.h> #include <linux/blkdev.h> #include <linux/elevator.h> #include <linux/bio.h> #include <linux/module.h> #include <linux/slab.h> #include <linux/init.h> #include <linux/compiler.h> #include <linux/blktrace_api.h> #include <linux/hash.h> #include <linux/uaccess.h> #include <linux/pm_runtime.h> #include <linux/blk-cgroup.h> #include <trace/events/block.h> #include "blk.h" #include "blk-mq-sched.h" #include "blk-wbt.h" static DEFINE_SPINLOCK(elv_list_lock); static LIST_HEAD(elv_list); /* * Merge hash stuff. */ #define rq_hash_key(rq) (blk_rq_pos(rq) + blk_rq_sectors(rq)) /* * Query io scheduler to see if the current process issuing bio may be * merged with rq. */ static int elv_iosched_allow_bio_merge(struct request *rq, struct bio *bio) { struct request_queue *q = rq->q; struct elevator_queue *e = q->elevator; if (e->uses_mq && e->type->ops.mq.allow_merge) return e->type->ops.mq.allow_merge(q, rq, bio); else if (!e->uses_mq && e->type->ops.sq.elevator_allow_bio_merge_fn) return e->type->ops.sq.elevator_allow_bio_merge_fn(q, rq, bio); return 1; } /* * can we safely merge with this request? */ bool elv_bio_merge_ok(struct request *rq, struct bio *bio) { if (!blk_rq_merge_ok(rq, bio)) return false; if (!elv_iosched_allow_bio_merge(rq, bio)) return false; return true; } EXPORT_SYMBOL(elv_bio_merge_ok); static struct elevator_type *elevator_find(const char *name) { struct elevator_type *e; list_for_each_entry(e, &elv_list, list) { if (!strcmp(e->elevator_name, name)) return e; } return NULL; } static void elevator_put(struct elevator_type *e) { module_put(e->elevator_owner); } static struct elevator_type *elevator_get(const char *name, bool try_loading) { struct elevator_type *e; spin_lock(&elv_list_lock); e = elevator_find(name); if (!e && try_loading) { spin_unlock(&elv_list_lock); request_module("%s-iosched", name); spin_lock(&elv_list_lock); e = elevator_find(name); } if (e && !try_module_get(e->elevator_owner)) e = NULL; spin_unlock(&elv_list_lock); return e; } static char chosen_elevator[ELV_NAME_MAX]; static int __init elevator_setup(char *str) { /* * Be backwards-compatible with previous kernels, so users * won't get the wrong elevator. */ strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1); return 1; } __setup("elevator=", elevator_setup); /* called during boot to load the elevator chosen by the elevator param */ void __init load_default_elevator_module(void) { struct elevator_type *e; if (!chosen_elevator[0]) return; spin_lock(&elv_list_lock); e = elevator_find(chosen_elevator); spin_unlock(&elv_list_lock); if (!e) request_module("%s-iosched", chosen_elevator); } static struct kobj_type elv_ktype; struct elevator_queue *elevator_alloc(struct request_queue *q, struct elevator_type *e) { struct elevator_queue *eq; eq = kzalloc_node(sizeof(*eq), GFP_KERNEL, q->node); if (unlikely(!eq)) return NULL; eq->type = e; kobject_init(&eq->kobj, &elv_ktype); mutex_init(&eq->sysfs_lock); hash_init(eq->hash); eq->uses_mq = e->uses_mq; return eq; } EXPORT_SYMBOL(elevator_alloc); static void elevator_release(struct kobject *kobj) { struct elevator_queue *e; e = container_of(kobj, struct elevator_queue, kobj); elevator_put(e->type); kfree(e); } int elevator_init(struct request_queue *q, char *name) { struct elevator_type *e = NULL; int err; /* * q->sysfs_lock must be held to provide mutual exclusion between * elevator_switch() and here. */ lockdep_assert_held(&q->sysfs_lock); if (unlikely(q->elevator)) return 0; INIT_LIST_HEAD(&q->queue_head); q->last_merge = NULL; q->end_sector = 0; q->boundary_rq = NULL; if (name) { e = elevator_get(name, true); if (!e) return -EINVAL; } /* * Use the default elevator specified by config boot param for * non-mq devices, or by config option. Don't try to load modules * as we could be running off async and request_module() isn't * allowed from async. */ if (!e && !q->mq_ops && *chosen_elevator) { e = elevator_get(chosen_elevator, false); if (!e) printk(KERN_ERR "I/O scheduler %s not found\n", chosen_elevator); } if (!e) { /* * For blk-mq devices, we default to using mq-deadline, * if available, for single queue devices. If deadline * isn't available OR we have multiple queues, default * to "none". */ if (q->mq_ops) { if (q->nr_hw_queues == 1) e = elevator_get("mq-deadline", false); if (!e) return 0; } else e = elevator_get(CONFIG_DEFAULT_IOSCHED, false); if (!e) { printk(KERN_ERR "Default I/O scheduler not found. " \ "Using noop.\n"); e = elevator_get("noop", false); } } if (e->uses_mq) err = blk_mq_init_sched(q, e); else err = e->ops.sq.elevator_init_fn(q, e); if (err) elevator_put(e); return err; } EXPORT_SYMBOL(elevator_init); void elevator_exit(struct request_queue *q, struct elevator_queue *e) { mutex_lock(&e->sysfs_lock); if (e->uses_mq && e->type->ops.mq.exit_sched) blk_mq_exit_sched(q, e); else if (!e->uses_mq && e->type->ops.sq.elevator_exit_fn) e->type->ops.sq.elevator_exit_fn(e); mutex_unlock(&e->sysfs_lock); kobject_put(&e->kobj); } EXPORT_SYMBOL(elevator_exit); static inline void __elv_rqhash_del(struct request *rq) { hash_del(&rq->hash); rq->rq_flags &= ~RQF_HASHED; } void elv_rqhash_del(struct request_queue *q, struct request *rq) { if (ELV_ON_HASH(rq)) __elv_rqhash_del(rq); } EXPORT_SYMBOL_GPL(elv_rqhash_del); void elv_rqhash_add(struct request_queue *q, struct request *rq) { struct elevator_queue *e = q->elevator; BUG_ON(ELV_ON_HASH(rq)); hash_add(e->hash, &rq->hash, rq_hash_key(rq)); rq->rq_flags |= RQF_HASHED; } EXPORT_SYMBOL_GPL(elv_rqhash_add); void elv_rqhash_reposition(struct request_queue *q, struct request *rq) { __elv_rqhash_del(rq); elv_rqhash_add(q, rq); } struct request *elv_rqhash_find(struct request_queue *q, sector_t offset) { struct elevator_queue *e = q->elevator; struct hlist_node *next; struct request *rq; hash_for_each_possible_safe(e->hash, rq, next, hash, offset) { BUG_ON(!ELV_ON_HASH(rq)); if (unlikely(!rq_mergeable(rq))) { __elv_rqhash_del(rq); continue; } if (rq_hash_key(rq) == offset) return rq; } return NULL; } /* * RB-tree support functions for inserting/lookup/removal of requests * in a sorted RB tree. */ void elv_rb_add(struct rb_root *root, struct request *rq) { struct rb_node **p = &root->rb_node; struct rb_node *parent = NULL; struct request *__rq; while (*p) { parent = *p; __rq = rb_entry(parent, struct request, rb_node); if (blk_rq_pos(rq) < blk_rq_pos(__rq)) p = &(*p)->rb_left; else if (blk_rq_pos(rq) >= blk_rq_pos(__rq)) p = &(*p)->rb_right; } rb_link_node(&rq->rb_node, parent, p); rb_insert_color(&rq->rb_node, root); } EXPORT_SYMBOL(elv_rb_add); void elv_rb_del(struct rb_root *root, struct request *rq) { BUG_ON(RB_EMPTY_NODE(&rq->rb_node)); rb_erase(&rq->rb_node, root); RB_CLEAR_NODE(&rq->rb_node); } EXPORT_SYMBOL(elv_rb_del); struct request *elv_rb_find(struct rb_root *root, sector_t sector) { struct rb_node *n = root->rb_node; struct request *rq; while (n) { rq = rb_entry(n, struct request, rb_node); if (sector < blk_rq_pos(rq)) n = n->rb_left; else if (sector > blk_rq_pos(rq)) n = n->rb_right; else return rq; } return NULL; } EXPORT_SYMBOL(elv_rb_find); /* * Insert rq into dispatch queue of q. Queue lock must be held on * entry. rq is sort instead into the dispatch queue. To be used by * specific elevators. */ void elv_dispatch_sort(struct request_queue *q, struct request *rq) { sector_t boundary; struct list_head *entry; if (q->last_merge == rq) q->last_merge = NULL; elv_rqhash_del(q, rq); q->nr_sorted--; boundary = q->end_sector; list_for_each_prev(entry, &q->queue_head) { struct request *pos = list_entry_rq(entry); if (req_op(rq) != req_op(pos)) break; if (rq_data_dir(rq) != rq_data_dir(pos)) break; if (pos->rq_flags & (RQF_STARTED | RQF_SOFTBARRIER)) break; if (blk_rq_pos(rq) >= boundary) { if (blk_rq_pos(pos) < boundary) continue; } else { if (blk_rq_pos(pos) >= boundary) break; } if (blk_rq_pos(rq) >= blk_rq_pos(pos)) break; } list_add(&rq->queuelist, entry); } EXPORT_SYMBOL(elv_dispatch_sort); /* * Insert rq into dispatch queue of q. Queue lock must be held on * entry. rq is added to the back of the dispatch queue. To be used by * specific elevators. */ void elv_dispatch_add_tail(struct request_queue *q, struct request *rq) { if (q->last_merge == rq) q->last_merge = NULL; elv_rqhash_del(q, rq); q->nr_sorted--; q->end_sector = rq_end_sector(rq); q->boundary_rq = rq; list_add_tail(&rq->queuelist, &q->queue_head); } EXPORT_SYMBOL(elv_dispatch_add_tail); enum elv_merge elv_merge(struct request_queue *q, struct request **req, struct bio *bio) { struct elevator_queue *e = q->elevator; struct request *__rq; /* * Levels of merges: * nomerges: No merges at all attempted * noxmerges: Only simple one-hit cache try * merges: All merge tries attempted */ if (blk_queue_nomerges(q) || !bio_mergeable(bio)) return ELEVATOR_NO_MERGE; /* * First try one-hit cache. */ if (q->last_merge && elv_bio_merge_ok(q->last_merge, bio)) { enum elv_merge ret = blk_try_merge(q->last_merge, bio); if (ret != ELEVATOR_NO_MERGE) { *req = q->last_merge; return ret; } } if (blk_queue_noxmerges(q)) return ELEVATOR_NO_MERGE; /* * See if our hash lookup can find a potential backmerge. */ __rq = elv_rqhash_find(q, bio->bi_iter.bi_sector); if (__rq && elv_bio_merge_ok(__rq, bio)) { *req = __rq; return ELEVATOR_BACK_MERGE; } if (e->uses_mq && e->type->ops.mq.request_merge) return e->type->ops.mq.request_merge(q, req, bio); else if (!e->uses_mq && e->type->ops.sq.elevator_merge_fn) return e->type->ops.sq.elevator_merge_fn(q, req, bio); return ELEVATOR_NO_MERGE; } /* * Attempt to do an insertion back merge. Only check for the case where * we can append 'rq' to an existing request, so we can throw 'rq' away * afterwards. * * Returns true if we merged, false otherwise */ bool elv_attempt_insert_merge(struct request_queue *q, struct request *rq) { struct request *__rq; bool ret; if (blk_queue_nomerges(q)) return false; /* * First try one-hit cache. */ if (q->last_merge && blk_attempt_req_merge(q, q->last_merge, rq)) return true;