linux-kernel - Re: [PATCH v1] kernel/trace:check the val against the available mem

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Date:   Wed, 4 Apr 2018 16:10:52 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Zhaoyang Huang <huangzhaoyang@...il.com>,
        Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
        kernel-patch-test@...ts.linaro.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Joel Fernandes <joelaf@...gle.com>, linux-mm@...ck.org,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH v1] kernel/trace:check the val against the available mem

On Wed 04-04-18 08:59:01, Steven Rostedt wrote:
[...]
> +       /*
> +        * Check if the available memory is there first.
> +        * Note, si_mem_available() only gives us a rough estimate of available
> +        * memory. It may not be accurate. But we don't care, we just want
> +        * to prevent doing any allocation when it is obvious that it is
> +        * not going to succeed.
> +        */
> +       i = si_mem_available();
> +       if (i < nr_pages)
> +               return -ENOMEM;
> +
> 
> Better?

I must be really missing something here. How can that work at all for
e.g. the zone_{highmem/movable}. You will get false on the above tests
even when you will have hard time to allocate anything from your
destination zones.
-- 
Michal Hocko
SUSE Labs