怎么做代刷网站长,实惠的网站建设公司,wordpress缩略图路径错误,管理员后台管理系统bio子系统学习一#xff1a;
主要源码目录 :block/bio.c include/linux/bio.h 内核版本#xff1a;4.19.1
这部分先总结下bio子系统的初始化部分#xff0c;后续再总结bio的申请以及释放#xff0c;还有其它api的使用等介绍。
bio的涉及到频繁的内存申请以及释放#x…bio子系统学习一
主要源码目录 :block/bio.c include/linux/bio.h 内核版本4.19.1
这部分先总结下bio子系统的初始化部分后续再总结bio的申请以及释放还有其它api的使用等介绍。
bio的涉及到频繁的内存申请以及释放包括bio结构体本身以及它比较重要的成员bi_io_vec*的内存申请和释放所以初始化部分主要是相关的内存池的初始化用于后面bio和bi_io_vec的内存申请和释放。
其中bio结构体和bio_vec结构体定义如下
/** main unit of I/O for the block layer and lower layers (ie drivers and* stacking drivers)*/
struct bio {struct bio *bi_next; /* request queue link */struct gendisk *bi_disk;unsigned int bi_opf; /* bottom bits req flags,* top bits REQ_OP. Use* accessors.*/unsigned short bi_flags; /* status, etc and bvec pool number */unsigned short bi_ioprio;unsigned short bi_write_hint;blk_status_t bi_status;u8 bi_partno;/* Number of segments in this BIO after* physical address coalescing is performed.*/unsigned int bi_phys_segments;/** To keep track of the max segment size, we account for the* sizes of the first and last mergeable segments in this bio.*/unsigned int bi_seg_front_size;unsigned int bi_seg_back_size;struct bvec_iter bi_iter; //用来遍历bvec标记bio的处理进度atomic_t __bi_remaining;bio_end_io_t *bi_end_io;void *bi_private;
#ifdef CONFIG_BLK_CGROUP/** Optional ioc and css associated with this bio. Put on bio* release. Read comment on top of bio_associate_current().*/struct io_context *bi_ioc;struct cgroup_subsys_state *bi_css;struct blkcg_gq *bi_blkg;struct bio_issue bi_issue;
#endifunion {
#if defined(CONFIG_BLK_DEV_INTEGRITY)struct bio_integrity_payload *bi_integrity; /* data integrity */
#endif};unsigned short bi_vcnt; /* how many bio_vecs *//** Everything starting with bi_max_vecs will be preserved by bio_reset()*/unsigned short bi_max_vecs; /* max bvl_vecs we can hold */atomic_t __bi_cnt; /* pin count */struct bio_vec *bi_io_vec; /* the actual vec list */struct bio_set *bi_pool;/** We can inline a number of vecs at the end of the bio, to avoid* double allocations for a small number of bio_vecs. This member* MUST obviously be kept at the very end of the bio.*/struct bio_vec bi_inline_vecs[0];
};
/** was unsigned short, but we might as well be ready for 64kB I/O pages*/
struct bio_vec {struct page *bv_page;unsigned int bv_len;unsigned int bv_offset;
};入口函数init_bio
其中bio_integrity_init函数和bioset_integrity_create函数先不看吧。
//这个是涉及到的结构体定义
struct bio_slab {struct kmem_cache *slab; //指向cache描述符cache描述符描述了slab信息unsigned int slab_ref; //bio_slab结构体的引用计数unsigned int slab_size; //内存池中object大小char name[8]; //内存池名称/proc/slabinfo可以看到
};static DEFINE_MUTEX(bio_slab_lock);
static struct bio_slab *bio_slabs;
static unsigned int bio_slab_nr, bio_slab_max;/*1:https://zhuanlan.zhihu.com/p/596543999?utm_id02:https://blog.csdn.net/geshifei/article/details/119959905
*/
static int __init init_bio(void)
{/*全局数组*/bio_slab_max 2;bio_slab_nr 0;bio_slabs kcalloc(bio_slab_max, sizeof(struct bio_slab), GFP_KERNEL);if (!bio_slabs)panic(bio: cant allocate bios\n);/*这部分先不看*/bio_integrity_init();//bvec_slabs数组管理bvec内存池biovec_init_slabs(); //分配bio_vec的高速内存池/*参数1:需要初始化的bio_set指针参数二:内存池中bio的最小数量参数三:struct bio结构体前附加数据块的大小front_padsizeof(struct bio)就是内存池中object的大小。从fs_bio_set类型内存池中申请bio内存块bio前无附加数据参数四:BIOSET_NEED_BVECS 创建一个单独的内存池用于分配iovecsfs_bio_set需设置该标记BIOSET_NEED_RESCUER创建一个workqueue处理函数为bio_alloc_rescue当内存不足无法从内存池中申请到bio时该workqueue把处理stack device时比如raid暂存在list中的bio参考后文“bio的提交”提交处理从而回收bio。对于非stack device场景不需要这个工作队列。对fs_bio_set这个变量进行初始化*/if (bioset_init(fs_bio_set, BIO_POOL_SIZE, 0, BIOSET_NEED_BVECS)) //2, 0 ,1panic(bio: cant allocate bios\n);/*这部分先不看*/if (bioset_integrity_create(fs_bio_set, BIO_POOL_SIZE)) //2panic(bio: cant create integrity pool\n);return 0;
}
subsys_initcall(init_bio);这里先分析下bio_slabs 这个结构体看变量名字也比较容易分析它是后续用于申请bio这个结构体时使用的只是初始化时它的数组下标只有两个且其成员也没有初始化在实际使用时它的成员才会进行初始化而且在必要时也会进行扩容也就是它的数组下标不是2了。(这个见bio_find_or_create_slab函数)所以在申请bio的时候根据算法的设计它有可能是从任何一个下标的成员(slab)当中申请内存的。
biovec_init_slabs函数分析
这个函数看名称也不难分析是对后续在申请biovec相关内存时做的一些初始化。
#define BIO_INLINE_VECS 4
/*1://https://blog.csdn.net/sinat_32960911/article/details/1322377812:__read_mostly gcc编译选项 标记该变量会被频繁访问 提高系统性能struct biovec_slab {int nr_vecs;char *name;struct kmem_cache *slab;};
*/
#define BV(x, n) { .nr_vecs x, .name biovec-#n }
static struct biovec_slab bvec_slabs[BVEC_POOL_NR] __read_mostly { BV(1, 1), BV(4, 4), BV(16, 16), BV(64, 64), BV(128, 128), BV(BIO_MAX_PAGES, max), //这个当作是256吧
};
#undef BV //取消该宏定义static void __init biovec_init_slabs(void)
{int i;for (i 0; i BVEC_POOL_NR; i) { //6int size;struct biovec_slab *bvs bvec_slabs i; //指向结构体数组的首地址if (bvs-nr_vecs BIO_INLINE_VECS) { //4, 前面两个成员bvs-slab NULL; continue;}/*这个size比较关键*/size bvs-nr_vecs * sizeof(struct bio_vec);bvs-slab kmem_cache_create(bvs-name, size, 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);}
}bioset_init函数分析
这里比较重要的是调用的bio_find_or_create_slab函数其余的就是对fs_bio_set这个结构体的一些成员变量进行初始化。
struct bio_set {struct kmem_cache *bio_slab;unsigned int front_pad;mempool_t bio_pool;mempool_t bvec_pool;
#if defined(CONFIG_BLK_DEV_INTEGRITY)mempool_t bio_integrity_pool;mempool_t bvec_integrity_pool;
#endif//Deadlock avoidance for stacking block drivers: see comments in bio_alloc_bioset() for detailsspinlock_t rescue_lock;struct bio_list rescue_list;struct work_struct rescue_work;struct workqueue_struct *rescue_workqueue;
};/** fs_bio_set is the bio_set containing bio and iovec memory pools used by* IO code that does not need private memory pools.*/
struct bio_set fs_bio_set;
EXPORT_SYMBOL(fs_bio_set);int bioset_init(struct bio_set *bs,unsigned int pool_size, unsigned int front_pad, int flags)
{//sizeof(bio)的多余部分unsigned int back_pad BIO_INLINE_VECS * sizeof(struct bio_vec); //4 * sizeof(struct bio_vec)bs-front_pad front_pad; //0spin_lock_init(bs-rescue_lock); //自旋锁初始化bio_list_init(bs-rescue_list); //bio_list 初始化INIT_WORK(bs-rescue_work, bio_alloc_rescue); //工作队列初始化/*返回的这个值也记录在这个bio_slabs全局数组里了看函数名称bio当中寻找slab或者创建一个slab*/bs-bio_slab bio_find_or_create_slab(front_pad back_pad); //0back_padif (!bs-bio_slab)return -ENOMEM;/*bio_pool的初始化后面分配内存使用mempool_allocpool_size内存池至少保留两个元素mempool_init(pool, min_nr, mempool_alloc_slab, mempool_free_slab, (void *) kc);后续申请内存走的是这个路线 - mempool_alloc_slab - kmem_cache_alloc*/if (mempool_init_slab_pool(bs-bio_pool, pool_size, bs-bio_slab))//2goto bad;//1 1 0)if ((flags BIOSET_NEED_BVECS) biovec_init_pool(bs-bvec_pool, pool_size)) //2goto bad;if (!(flags BIOSET_NEED_RESCUER)) // 1 (1 1) - 0001 0010return 0;bs-rescue_workqueue alloc_workqueue(bioset, WQ_MEM_RECLAIM, 0); //申请一个工作队列if (!bs-rescue_workqueue)goto bad;return 0;
bad:bioset_exit(bs);return -ENOMEM;
}
EXPORT_SYMBOL(bioset_init);bio_find_or_create_slab函数分析
static struct kmem_cache *bio_find_or_create_slab(unsigned int extra_size)
{unsigned int sz sizeof(struct bio) extra_size; struct kmem_cache *slab NULL;struct bio_slab *bslab, *new_bio_slabs;unsigned int new_bio_slab_max;unsigned int i, entry -1;mutex_lock(bio_slab_lock);/*遍历bio_slabs数组若某个bio_slab-slab_size等于sz,那么就选择这个bio_slab.*/i 0;while (i bio_slab_nr) { //这个一开始是0bslab bio_slabs[i];//若bio_slabs有空闲未用的bio_slab选择该bio_slabif (!bslab-slab entry -1)entry i;else if (bslab-slab_size sz) {slab bslab-slab;bslab-slab_ref;break;}i;}//找到bio_slab了if (slab)goto out_unlock;/*经过上面两步依然未找到可用的bio_slab通过krealloc将bio_slabs数组长度扩大一倍并选择其中一个空闲的bio_slab。*/if (bio_slab_nr bio_slab_max entry -1) {new_bio_slab_max bio_slab_max 1; //相当于乘以2new_bio_slabs krealloc(bio_slabs, new_bio_slab_max * sizeof(struct bio_slab), GFP_KERNEL);if (!new_bio_slabs)goto out_unlock;bio_slab_max new_bio_slab_max;bio_slabs new_bio_slabs;}if (entry -1)entry bio_slab_nr;bslab bio_slabs[entry];snprintf(bslab-name, sizeof(bslab-name), bio-%d, entry);slab kmem_cache_create(bslab-name, sz, ARCH_KMALLOC_MINALIGN, SLAB_HWCACHE_ALIGN, NULL);if (!slab)goto out_unlock;bslab-slab slab;bslab-slab_ref 1;bslab-slab_size sz;
out_unlock:mutex_unlock(bio_slab_lock);return slab;
}其初始化过程基本就是这样了如果对内存池用的不多也不要紧可以看看相关源码也不多。
总结初始化部分如果光光看这部分会比较晦涩后面在涉及到bio的申请和释放时再回头来看初始化部分就清晰许多了。
