The patch titled
Subject: mm/compaction: make proactive compaction high watermark configurable via sysctl
has been added to the -mm mm-unstable branch. Its filename is
mm-compaction-make-proactive-compaction-high-watermark-configurable-via-sysctl.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-compaction-make-proactive-compaction-high-watermark-configurable-via-sysctl.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Michal Clapinski <mclapinski@xxxxxxxxxx>
Subject: mm/compaction: make proactive compaction high watermark configurable via sysctl
Date: Mon, 27 Jan 2025 22:50:20 +0100
Currently, the difference between the high and low watermarks for
proactive compaction is hardcoded to 10. This hardcoded difference is too
large for free page reporting to work well.
Add a new sysctl, `compaction_proactiveness_leeway`, to control the
difference between the high and low watermarks.
Link: https://lkml.kernel.org/r/20250127215020.4023545-3-mclapinski@xxxxxxxxxx
Signed-off-by: Michal Clapinski <mclapinski@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/admin-guide/sysctl/vm.rst | 17 +++++++++++++++++
mm/compaction.c | 12 +++++++++++-
2 files changed, 28 insertions(+), 1 deletion(-)
--- a/Documentation/admin-guide/sysctl/vm.rst~mm-compaction-make-proactive-compaction-high-watermark-configurable-via-sysctl
+++ a/Documentation/admin-guide/sysctl/vm.rst
@@ -27,6 +27,7 @@ Currently, these files are in /proc/sys/
- admin_reserve_kbytes
- compact_memory
- compaction_proactiveness
+- compaction_proactiveness_leeway
- compact_unevictable_allowed
- dirty_background_bytes
- dirty_background_ratio
@@ -133,6 +134,22 @@ proactive compaction is not being effect
Be careful when setting it to extreme values like 100, as that may
cause excessive background compaction activity.
+compaction_proactiveness_leeway
+===============================
+
+This tunable controls the difference between high and low watermarks for
+proactive compaction. This tunable takes a value in the range [0, 100] with
+a default value of 10. Higher values will result in proactive compaction
+triggering less often but doing more work when it does trigger.
+
+Proactive compaction triggers when fragmentation score (lower is better) gets
+larger than high watermark. Compaction stops when the score gets smaller or
+equal to low watermark (or when no progress is being made).
+The watermarks are calculated as follows:
+
+low_wmark = 100 - compaction_proactiveness;
+high_wmark = low_wmark + compaction_proactiveness_leeway;
+
compact_unevictable_allowed
===========================
--- a/mm/compaction.c~mm-compaction-make-proactive-compaction-high-watermark-configurable-via-sysctl
+++ a/mm/compaction.c
@@ -1924,6 +1924,7 @@ static int sysctl_compact_unevictable_al
* background. It takes values in the range [0, 100].
*/
static unsigned int __read_mostly sysctl_compaction_proactiveness = 20;
+static unsigned int __read_mostly sysctl_compaction_proactiveness_leeway = 10;
static int sysctl_extfrag_threshold = 500;
static int __read_mostly sysctl_compact_memory;
@@ -2257,7 +2258,7 @@ static unsigned int fragmentation_score_
* close to 100 (maximum).
*/
wmark_low = 100U - sysctl_compaction_proactiveness;
- return low ? wmark_low : min(wmark_low + 10, 100U);
+ return low ? wmark_low : min(wmark_low + sysctl_compaction_proactiveness_leeway, 100U);
}
static bool should_proactive_compact_node(pg_data_t *pgdat)
@@ -3308,6 +3309,15 @@ static struct ctl_table vm_compaction[]
.mode = 0644,
.proc_handler = compaction_proactiveness_sysctl_handler,
.extra1 = SYSCTL_ZERO,
+ .extra2 = SYSCTL_ONE_HUNDRED,
+ },
+ {
+ .procname = "compaction_proactiveness_leeway",
+ .data = &sysctl_compaction_proactiveness_leeway,
+ .maxlen = sizeof(sysctl_compaction_proactiveness_leeway),
+ .mode = 0644,
+ .proc_handler = compaction_proactiveness_sysctl_handler,
+ .extra1 = SYSCTL_ZERO,
.extra2 = SYSCTL_ONE_HUNDRED,
},
{
_
Patches currently in -mm which might be from mclapinski@xxxxxxxxxx are
mm-compaction-remove-low-watermark-cap-for-proactive-compaction.patch
mm-compaction-make-proactive-compaction-high-watermark-configurable-via-sysctl.patch
