linux-kernel - Re: Possible mem cgroup bug in kernels between 4.18.0 and 5.3-rc1.

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Message-ID: <20190802081808.GB6461@dhcp22.suse.cz>
Date:   Fri, 2 Aug 2019 10:18:08 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Hillf Danton <hdanton@...a.com>
Cc:     Masoud Sharbiani <msharbiani@...le.com>, hannes@...xchg.org,
        vdavydov.dev@...il.com, linux-mm@...ck.org,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        Greg KH <gregkh@...uxfoundation.org>
Subject: Re: Possible mem cgroup bug in kernels between 4.18.0 and 5.3-rc1.

[Hillf, your email client or workflow mangles emails. In this case you
are seem to be reusing the message id from the email you are replying to
which confuses my email client to assume your email is a duplicate.]

On Fri 02-08-19 16:08:01, Hillf Danton wrote:
[...]
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2547,8 +2547,12 @@ retry:
>  	nr_reclaimed = try_to_free_mem_cgroup_pages(mem_over_limit, nr_pages,
>  						    gfp_mask, may_swap);
>  
> -	if (mem_cgroup_margin(mem_over_limit) >= nr_pages)
> -		goto retry;
> +	if (mem_cgroup_margin(mem_over_limit) >= nr_pages) {
> +		if (nr_retries--)
> +			goto retry;
> +		/* give up charging memhog */
> +		return -ENOMEM;
> +	}

Huh, what? You are effectively saying that we should fail the charge
when the requested nr_pages would fit in. This doesn't make much sense
to me. What are you trying to achive here?
-- 
Michal Hocko
SUSE Labs