On 3/19/20 5:39 PM, Sebastian Andrzej Siewior wrote:
> Since commit
> 5bbe3547aa3ba ("mm: allow compaction of unevictable pages")
>
> it is allowed to examine mlocked pages and compact them by default.
> On -RT even minor pagefaults are problematic because it may take a few
> 100us to resolve them and until then the task is blocked.
>
> Make compact_unevictable_allowed = 0 default and issue a warning on RT
> if it is changed.
>
> Link: https://lore.kernel.org/linux-mm/20190710144138.qyn4tuttdq6h7kqx@xxxxxxxxxxxxx/
> Acked-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Nit below:
> @@ -2572,6 +2577,28 @@ int proc_dointvec(struct ctl_table *table, int write,
> return do_proc_dointvec(table, write, buffer, lenp, ppos, NULL, NULL);
> }
>
> +#ifdef CONFIG_COMPACTION
> +static int proc_dointvec_minmax_warn_RT_change(struct ctl_table *table,
> + int write, void __user *buffer,
> + size_t *lenp, loff_t *ppos)
> +{
> + int ret, old;
> +
> + if (!IS_ENABLED(CONFIG_PREEMPT_RT) || !write)
> + return proc_dointvec_minmax(table, write, buffer, lenp, ppos);
> +
> + old = *(int *)table->data;
> + ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
> + if (ret)
> + return ret;
> + if (old != *(int *)table->data)
> + pr_warn_once("sysctl attribute %s changed changed by %s[%d]\n",
^ "changed" twice
> + table->procname, current->comm,
> + task_pid_nr(current));
> + return ret;
> +}
> +#endif
> +
> /**
> * proc_douintvec - read a vector of unsigned integers
> * @table: the sysctl table
