Re: [PATCH resend] memcg: introduce per-memcg reclaim interface

[Wei Xu]

On Mon, Apr 4, 2022 at 10:08 AM Shakeel Butt <shakeelb@xxxxxxxxxx> wrote:
>
> On Fri, Apr 1, 2022 at 1:14 PM Wei Xu <weixugc@xxxxxxxxxx> wrote:
> >
> [...]
> >
> > -EAGAIN sounds good, too.  Given that the userspace requests to
> > reclaim a specified number of bytes, I think it is generally better to
> > tell the userspace whether the request has been successfully
> > fulfilled. Ideally, it would be even better to return how many bytes
> > that have been reclaimed, though that is not easy to do through the
> > cgroup interface.
>
> What would be the challenge on returning the number of bytes reclaimed
> through cgroup interface?

write() syscall is used to write the command into memory.reclaim,
which should return either the number of command bytes written or -1
(errno is set to indicate the actual error).  I think we should not
return the number of bytes reclaimed through write().  A new
sys_reclaim() is better in this regard because we can define its
return value, though it would need a cgroup argument, which is not
commonly defined for syscalls.