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