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* [PATCH] mm/compaction: Disable compact_unevictable_allowed on RT
@ 2020-01-15 16:10 Sebastian Andrzej Siewior
  2020-01-15 22:04 ` Vlastimil Babka
  0 siblings, 1 reply; 18+ messages in thread
From: Sebastian Andrzej Siewior @ 2020-01-15 16:10 UTC (permalink / raw)
  To: linux-mm
  Cc: Thomas Gleixner, Vlastimil Babka, Andrew Morton,
	Luis Chamberlain, Kees Cook, Iurii Zaikin,
	Sebastian Andrzej Siewior

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 remove it from /proc on
RT.

Link: https://lore.kernel.org/linux-mm/20190710144138.qyn4tuttdq6h7kqx@linutronix.de/
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 kernel/sysctl.c | 3 ++-
 mm/compaction.c | 4 ++++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 70665934d53e2..d08bd51a0fbc3 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1488,6 +1488,7 @@ static struct ctl_table vm_table[] = {
 		.extra1		= &min_extfrag_threshold,
 		.extra2		= &max_extfrag_threshold,
 	},
+#ifndef CONFIG_PREEMPT_RT
 	{
 		.procname	= "compact_unevictable_allowed",
 		.data		= &sysctl_compact_unevictable_allowed,
@@ -1497,7 +1498,7 @@ static struct ctl_table vm_table[] = {
 		.extra1		= SYSCTL_ZERO,
 		.extra2		= SYSCTL_ONE,
 	},
-
+#endif
 #endif /* CONFIG_COMPACTION */
 	{
 		.procname	= "min_free_kbytes",
diff --git a/mm/compaction.c b/mm/compaction.c
index 672d3c78c6abf..b2c804c35ae56 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1590,7 +1590,11 @@ typedef enum {
  * Allow userspace to control policy on scanning the unevictable LRU for
  * compactable pages.
  */
+#ifdef CONFIG_PREEMPT_RT
+#define sysctl_compact_unevictable_allowed 0
+#else
 int sysctl_compact_unevictable_allowed __read_mostly = 1;
+#endif
 
 static inline void
 update_fast_start_pfn(struct compact_control *cc, unsigned long pfn)
-- 
2.25.0.rc2



^ permalink raw reply related	[flat|nested] 18+ messages in thread

end of thread, other threads:[~2020-03-19 16:55 UTC | newest]

Thread overview: 18+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-01-15 16:10 [PATCH] mm/compaction: Disable compact_unevictable_allowed on RT Sebastian Andrzej Siewior
2020-01-15 22:04 ` Vlastimil Babka
2020-01-16 10:22   ` Sebastian Andrzej Siewior
2020-03-02 17:35   ` [PATCH v2] " Sebastian Andrzej Siewior
2020-03-02 21:25     ` Andrew Morton
2020-03-03 17:59       ` Sebastian Andrzej Siewior
2020-03-03 20:20         ` [PATCH 1/2] =?UTF-8?q?mm/compaction:=20Really=20limit=20compact?= =?UTF-8?q?=5Funevictable=5Fallowed=20to=200=E2=80=A61?= Sebastian Andrzej Siewior
2020-03-03 20:22           ` [PATCH 2/2 v3] mm/compaction: Disable compact_unevictable_allowed on RT Sebastian Andrzej Siewior
2020-03-03 23:56             ` Andrew Morton
2020-03-04  8:19               ` Vlastimil Babka
2020-03-04  9:27                 ` Sebastian Andrzej Siewior
2020-03-19 16:39               ` [PATCH 2/2 v4] " Sebastian Andrzej Siewior
2020-03-19 16:49                 ` Vlastimil Babka
2020-03-19 16:55                   ` [PATCH 2/2 v5] " Sebastian Andrzej Siewior
2020-03-04  8:18             ` [PATCH 2/2 v3] " Vlastimil Babka
2020-03-04  9:25               ` Sebastian Andrzej Siewior
2020-03-04  9:11             ` Mel Gorman
2020-03-04  8:12           ` [PATCH 1/2] mm/compaction: Really limit compact_unevictable_allowed to 0…1 Vlastimil Babka

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