Re: [PATCH -next] mm: memcg: remove redundant seq_buf_has_overflowed()

[Michal Hocko <mhocko@suse.com>]

On Thu 27-06-24 16:33:00, xiujianfeng wrote:
> 
> 
> On 2024/6/27 15:13, Michal Hocko wrote:
> > On Wed 26-06-24 09:42:32, Xiu Jianfeng wrote:
> >> Both the end of memory_stat_format() and memcg_stat_format() will call
> >> WARN_ON_ONCE(seq_buf_has_overflowed()). However, memory_stat_format()
> >> is the only caller of memcg_stat_format(), when memcg is on the default
> >> hierarchy, seq_buf_has_overflowed() will be executed twice, so remove
> >> the reduntant one.
> > 
> > Shouldn't we rather remove both? Are they giving us anything useful
> > actually? Would a simpl pr_warn be sufficient? Afterall all we care
> > about is to learn that we need to grow the buffer size because our stats
> > do not fit anymore. It is not really important whether that is an OOM or
> > cgroupfs interface path.
> 
> I did a test, when I removed both of them and added a lot of prints in
> memcg_stat_format() to make the seq_buf overflow, and then cat
> memory.stat in user mode, no OOM occurred, and there were no warning
> logs in the kernel.

The default buffer size is PAGE_SIZE.

-- 
Michal Hocko
SUSE Labs