Re: [PATCH 2/2 v3] mm/compaction: Disable compact_unevictable_allowed on RT
From: Andrew Morton <akpm@linux-foundation.org>
Date: 2020-03-03 23:56:38
Also in:
linux-mm
On Tue, 3 Mar 2020 21:22:25 +0100 Sebastian Andrzej Siewior [off-list ref] 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.Fair enough, I guess.
quoted hunk ↗ jump to hunk
@@ -2572,6 +2577,26 @@ 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_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(table, write, buffer, lenp, ppos); + + old = *(int *)table->data; + ret = proc_dointvec(table, write, buffer, lenp, ppos); + if (ret) + return ret; + WARN_ONCE(old != *(int *)table->data, "sysctl attribute %s changed.", + table->procname);
The WARN will include a stack trace which just isn't interesting. A pr_warn() would be better?
+ return ret; +} +#endif