memcg: use seq_buf_do_printk() with mem_cgroup_print_oom_meminfo()

Currently, we format all the memcg stats into a buffer in
mem_cgroup_print_oom_meminfo() and use pr_info() to dump it to the logs. 
However, this buffer is large in size.  Although it is currently working
as intended, ther is a dependency between the memcg stats buffer and the
printk record size limit.

If we add more stats in the future and the buffer becomes larger than the
printk record size limit, or if the prink record size limit is reduced,
the logs may be truncated.

It is safer to use seq_buf_do_printk(), which will automatically break up
the buffer at line breaks and issue small printk() calls.

Refactor the code to move the seq_buf from memory_stat_format() to its
callers, and use seq_buf_do_printk() to print the seq_buf in
mem_cgroup_print_oom_meminfo().

Link: https://lkml.kernel.org/r/20230428132406.2540811-2-yosryahmed@google.com


Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Shakeel Butt <shakeelb@google.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>