include/linux/iocontext.h

   1 #ifndef IOCONTEXT_H
   2 #define IOCONTEXT_H
   3
   4 #include <linux/radix-tree.h>
   5 #include <linux/rcupdate.h>
   6 #include <linux/workqueue.h>
   7
   8 enum {
   9         ICQ_IOPRIO_CHANGED      = 1 << 0,
  10         ICQ_CGROUP_CHANGED      = 1 << 1,
  11
  12         ICQ_CHANGED_MASK        = ICQ_IOPRIO_CHANGED | ICQ_CGROUP_CHANGED,
  13 };
  14
  15 /*
  16  * An io_cq (icq) is association between an io_context (ioc) and a
  17  * request_queue (q).  This is used by elevators which need to track
  18  * information per ioc - q pair.
  19  *
  20  * Elevator can request use of icq by setting elevator_type->icq_size and
  21  * ->icq_align.  Both size and align must be larger than that of struct
  22  * io_cq and elevator can use the tail area for private information.  The
  23  * recommended way to do this is defining a struct which contains io_cq as
  24  * the first member followed by private members and using its size and
  25  * align.  For example,
  26  *
  27  *      struct snail_io_cq {
  28  *              struct io_cq    icq;
  29  *              int             poke_snail;
  30  *              int             feed_snail;
  31  *      };
  32  *
  33  *      struct elevator_type snail_elv_type {
  34  *              .ops =          { ... },
  35  *              .icq_size =     sizeof(struct snail_io_cq),
  36  *              .icq_align =    __alignof__(struct snail_io_cq),
  37  *              ...
  38  *      };
  39  *
  40  * If icq_size is set, block core will manage icq's.  All requests will
  41  * have its ->elv.icq field set before elevator_ops->elevator_set_req_fn()
  42  * is called and be holding a reference to the associated io_context.
  43  *
  44  * Whenever a new icq is created, elevator_ops->elevator_init_icq_fn() is
  45  * called and, on destruction, ->elevator_exit_icq_fn().  Both functions
  46  * are called with both the associated io_context and queue locks held.
  47  *
  48  * Elevator is allowed to lookup icq using ioc_lookup_icq() while holding
  49  * queue lock but the returned icq is valid only until the queue lock is
  50  * released.  Elevators can not and should not try to create or destroy
  51  * icq's.
  52  *
  53  * As icq's are linked from both ioc and q, the locking rules are a bit
  54  * complex.
  55  *
  56  * - ioc lock nests inside q lock.
  57  *
  58  * - ioc->icq_list and icq->ioc_node are protected by ioc lock.
  59  *   q->icq_list and icq->q_node by q lock.
  60  *
  61  * - ioc->icq_tree and ioc->icq_hint are protected by ioc lock, while icq
  62  *   itself is protected by q lock.  However, both the indexes and icq
  63  *   itself are also RCU managed and lookup can be performed holding only
  64  *   the q lock.
  65  *
  66  * - icq's are not reference counted.  They are destroyed when either the
  67  *   ioc or q goes away.  Each request with icq set holds an extra
  68  *   reference to ioc to ensure it stays until the request is completed.
  69  *
  70  * - Linking and unlinking icq's are performed while holding both ioc and q
  71  *   locks.  Due to the lock ordering, q exit is simple but ioc exit
  72  *   requires reverse-order double lock dance.
  73  */
  74 struct io_cq {
  75         struct request_queue    *q;
  76         struct io_context       *ioc;
  77
  78         /*
  79          * q_node and ioc_node link io_cq through icq_list of q and ioc
  80          * respectively.  Both fields are unused once ioc_exit_icq() is
  81          * called and shared with __rcu_icq_cache and __rcu_head which are
  82          * used for RCU free of io_cq.
  83          */
  84         union {
  85                 struct list_head        q_node;
  86                 struct kmem_cache       *__rcu_icq_cache;
  87         };
  88         union {
  89                 struct hlist_node       ioc_node;
  90                 struct rcu_head         __rcu_head;
  91         };
  92
  93         unsigned int            flags;
  94 };
  95
  96 /*
  97  * I/O subsystem state of the associated processes.  It is refcounted
  98  * and kmalloc'ed. These could be shared between processes.
  99  */
 100 struct io_context {
 101         atomic_long_t refcount;
 102         atomic_t nr_tasks;
 103
 104         /* all the fields below are protected by this lock */
 105         spinlock_t lock;
 106
 107         unsigned short ioprio;
 108
 109         /*
 110          * For request batching
 111          */
 112         int nr_batch_requests;     /* Number of requests left in the batch */
 113         unsigned long last_waited; /* Time last woken after wait for request */
 114
 115         struct radix_tree_root  icq_tree;
 116         struct io_cq __rcu      *icq_hint;
 117         struct hlist_head       icq_list;
 118
 119         struct work_struct release_work;
 120 };
 121
 122 static inline struct io_context *ioc_task_link(struct io_context *ioc)
 123 {
 124         /*
 125          * if ref count is zero, don't allow sharing (ioc is going away, it's
 126          * a race).
 127          */
 128         if (ioc && atomic_long_inc_not_zero(&ioc->refcount)) {
 129                 atomic_inc(&ioc->nr_tasks);
 130                 return ioc;
 131         }
 132
 133         return NULL;
 134 }
 135
 136 struct task_struct;
 137 #ifdef CONFIG_BLOCK
 138 void put_io_context(struct io_context *ioc);
 139 void exit_io_context(struct task_struct *task);
 140 struct io_context *get_task_io_context(struct task_struct *task,
 141                                        gfp_t gfp_flags, int node);
 142 void ioc_ioprio_changed(struct io_context *ioc, int ioprio);
 143 void ioc_cgroup_changed(struct io_context *ioc);
 144 unsigned int icq_get_changed(struct io_cq *icq);
 145 #else
 146 struct io_context;
 147 static inline void put_io_context(struct io_context *ioc) { }
 148 static inline void exit_io_context(struct task_struct *task) { }
 149 #endif
 150
 151 #endif