struct task_struct有struct task_io_accounting ioac;

struct task_io_accounting {#ifdef CONFIG_TASK_XACCT    /* bytes read */    u64 rchar;    /*  bytes written */    u64 wchar;    /* # of read syscalls */    u64 syscr;    /* # of write syscalls */    u64 syscw;#endif /* CONFIG_TASK_XACCT */#ifdef CONFIG_TASK_IO_ACCOUNTING    /*     * The number of bytes which this task has caused to be read from     * storage.     */    u64 read_bytes;    /*     * The number of bytes which this task has caused, or shall cause to be     * written to disk.     */    u64 write_bytes;    /*     * A task can cause "negative" IO too.  If this task truncates some     * dirty pagecache, some IO which another task has been accounted for     * (in its write_bytes) will not be happening.  We _could_ just     * subtract that from the truncating task's write_bytes, but there is     * information loss in doing that.     */    u64 cancelled_write_bytes;#endif /* CONFIG_TASK_IO_ACCOUNTING */};

每个task_struct内嵌的write_bytes，统计是该过程写内存的字节数，这个写的，以后时刻可能还在内存外面，不肯定写到磁盘里了。

void __set_page_dirty(struct page *page, struct address_space *mapping,                 int warn){    unsigned long flags;    xa_lock_irqsave(&mapping->i_pages, flags);    if (page->mapping) {    /* Race with truncate? */        WARN_ON_ONCE(warn && !PageUptodate(page));        account_page_dirtied(page, mapping);        __xa_set_mark(&mapping->i_pages, page_index(page),                PAGECACHE_TAG_DIRTY);    }    xa_unlock_irqrestore(&mapping->i_pages, flags);}
static void account_page_dirtied(struct page *page,        struct address_space *mapping){    struct inode *inode = mapping->host;    trace_writeback_dirty_page(page, mapping);    if (mapping_can_writeback(mapping)) {        struct bdi_writeback *wb;        inode_attach_wb(inode, page);        wb = inode_to_wb(inode);        __inc_lruvec_page_state(page, NR_FILE_DIRTY);        __inc_zone_page_state(page, NR_ZONE_WRITE_PENDING);        __inc_node_page_state(page, NR_DIRTIED);        inc_wb_stat(wb, WB_RECLAIMABLE);        inc_wb_stat(wb, WB_DIRTIED);        task_io_account_write(PAGE_SIZE);        current->nr_dirtied++;        __this_cpu_inc(bdp_ratelimits);        mem_cgroup_track_foreign_dirty(page, wb);    }}
static inline void task_io_account_write(size_t bytes){    current->ioac.write_bytes += bytes;}