raid5_cache.c数据结构之r5l_io_unit

结构体代码

struct r5l_log {struct md_rdev *rdev;u32 uuid_checksum;sector_t device_size;/* log device size, round to * BLOCK_SECTORS */sector_t max_free_space;/* reclaim run if free space is at * this size */sector_t last_checkpoint;/* log tail. where recovery scan * starts from */u64 last_cp_seq;/* log tail sequence */sector_t log_start;/* log head. where new data appends */u64 seq;/* log head sequence */sector_t next_checkpoint;u64 next_cp_seq;struct mutex io_mutex;struct r5l_io_unit *current_io;/* current io_unit accepting new data */spinlock_t io_list_lock;struct list_head running_ios;/* io_units which are still running, * and have not yet been completely * written to the log */struct list_head io_end_ios;/* io_units which have been completely * written to the log but not yet written * to the RAID */struct list_head flushing_ios;/* io_units which are waiting for log * cache flush */struct list_head finished_ios;/* io_units which settle down in log disk */struct bio flush_bio;struct kmem_cache *io_kc;struct md_thread *reclaim_thread;unsigned long reclaim_target;/* number of space that need to be * reclaimed.  if it's 0, reclaim spaces * used by io_units which are in * IO_UNIT_STRIPE_END state (eg, reclaim * dones't wait for specific io_unit * switching to IO_UNIT_STRIPE_END * state) */wait_queue_head_t iounit_wait;struct list_head no_space_stripes; /* pending stripes, log has no space */spinlock_t no_space_stripes_lock;bool need_cache_flush;bool in_teardown;};

一、几个重要的元素

log_start

功能：新数据在log中的起始扇区

变化：向磁盘写新页的时候，扇区加8（为什么是8呢，因为默认一页是8个扇区呀）

current_io

功能：正在接收数据的结构体

初始化：创建meta时，log->current_io = r5l_new_meta(log)

删除：写log的时候，log->current_io = NULL

二、链表

running_ios：

功能：组织接收数据，没有完全写入log的io

初始化：初始化log的时候，INIT_LIST_HEAD(&log->running_ios)

进：创建meta的时候，io加入list_add_tail(&io->log_sibling, &log->running_ios)

出：如果io的state位是IO_UNIT_IO_END，io就会从running_ios移到finished_ios

io_end_ios：

功能：组织写入log，没有写入RAID的io（need_cache_flush）

初始化：初始化log的时候，INIT_LIST_HEAD(&log->io_end_ios)

进：当log->need_cache_flush为真的时候，r5l_move_io_unit_list(&log->running_ios, &log->io_end_ios,  IO_UNIT_IO_END);

出：加到flushing_ios ;list_splice_tail_init(&log->io_end_ios, &log->flushing_ios)

flushing_ios

功能：组织flush的io

初始化：初始化log的时候，INIT_LIST_HEAD(&log->flushing_ios)

进：

出：从io->stripe_list取下来后，提交sh，list_splice_tail_init(&log->flushing_ios, &log->finished_ios)

finished_ios

功能：组织已经写入log的io

初始化：初始化log的时候，INIT_LIST_HEAD(&log->finished_ios)

进；

出：r5l_complete_finished_ios，

no_space_stripes

功能：因log没有空间而pending的条带

初始化：

进：准备写log时，log没有空间存放，list_add_tail(&sh->log_list, &log->no_space_stripes)

出：log空间回收后，sh = list_first_entry(&log->no_space_stripes, struct stripe_head, log_list); list_del_init(&sh->log_list); 接着set_bit(STRIPE_HANDLE, &sh->state); raid5_release_stripe(sh)

三、几个有点难的元素

struct kmem_cache *io_kc：

赋值：log->io_kc = KMEM_CACHE(r5l_io_unit, 0)

使用：申请io，io = kmem_cache_zalloc(log->io_kc, GFP_NOIO | __GFP_NOFAIL)

释放：kmem_cache_destroy(log->io_kc)

struct md_thread *reclain_target

功能：回收的线程

wait_queue_head_t iounit_wait

初始化：init_waitqueue_head(&log->iounit_wait)

唤醒：wake_up(&log->iounit_wait)

使用：回收的时候wait_event_lock_irq(log->iounit_wait, r5l_reclaimable_space(log) > reclaimable, log->io_list_lock);