Re: [PATCH] mm, memcg: fix error return value of mem_cgroup_alloc()

[Yafang Shao <laoar.shao@gmail.com>]

On Mon, Apr 6, 2020 at 9:05 PM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Mon, Apr 06, 2020 at 08:54:07AM -0400, Yafang Shao wrote:
> > When I run my memcg testcase which creates lots of memcgs, I found
> > there're unexpected out of memory logs while there're still enough
> > available free memory. The error log is,
> > mkdir: cannot create directory 'foo.65533': Cannot allocate memory
> >
> > The reason is when we try to create more than MEM_CGROUP_ID_MAX memcgs, an
> > -ENOMEM errno will be set by mem_cgroup_css_alloc(), but the right errno
> > should be -ENOSPC, as explained above the function idr_alloc().
>
> I think idr_alloc() is wrong.  I think the right errno to return here is
> EBUSY "Device or resource busy".
>

Agree with you that EBUSY is better.
I will correct it.

> > -static struct mem_cgroup *mem_cgroup_alloc(void)
> > +static struct mem_cgroup *mem_cgroup_alloc(long *error)
>
> The normal way to do this is to return an ERR_PTR().  See
> include/linux/err.h.
>

Thanks for your advise. I will take a look at it.


Thanks
Yafang