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linux/debian/patches/patchset-zen/sauce/0020-ZEN-INTERACTIVE-mm-Disable-watermark-boosting-by-def.patch

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From 5f16843397798d2c709e3b8af4b1a73539d13aa8 Mon Sep 17 00:00:00 2001
From: Sultan Alsawaf <sultan@kerneltoast.com>
Date: Sat, 28 Mar 2020 13:06:28 -0700
Subject: ZEN: INTERACTIVE: mm: Disable watermark boosting by default
What watermark boosting does is preemptively fire up kswapd to free
memory when there hasn't been an allocation failure. It does this by
increasing kswapd's high watermark goal and then firing up kswapd. The
reason why this causes freezes is because, with the increased high
watermark goal, kswapd will steal memory from processes that need it in
order to make forward progress. These processes will, in turn, try to
allocate memory again, which will cause kswapd to steal necessary pages
from those processes again, in a positive feedback loop known as page
thrashing. When page thrashing occurs, your system is essentially
livelocked until the necessary forward progress can be made to stop
processes from trying to continuously allocate memory and trigger
kswapd to steal it back.
This problem already occurs with kswapd *without* watermark boosting,
but it's usually only encountered on machines with a small amount of
memory and/or a slow CPU. Watermark boosting just makes the existing
problem worse enough to notice on higher spec'd machines.
Disable watermark boosting by default since it's a total dumpster fire.
I can't imagine why anyone would want to explicitly enable it, but the
option is there in case someone does.
Signed-off-by: Sultan Alsawaf <sultan@kerneltoast.com>
---
init/Kconfig | 1 +
mm/page_alloc.c | 4 ++++
2 files changed, 5 insertions(+)
--- a/init/Kconfig
+++ b/init/Kconfig
2024-12-05 18:46:18 +03:00
@@ -160,6 +160,7 @@ config ZEN_INTERACTIVE
MG-LRU minimum cache TTL.......: 0 -> 1000 ms
Compact unevictable............: yes -> no
Compaction proactiveness.......: 20 -> 0
+ Watermark boost factor.........: 1.5 -> 0
--- EEVDF CPU Scheduler --------------------------------
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -271,7 +271,11 @@ const char * const migratetype_names[MIG
int min_free_kbytes = 1024;
int user_min_free_kbytes = -1;
+#ifdef CONFIG_ZEN_INTERACTIVE
+static int watermark_boost_factor __read_mostly;
+#else
static int watermark_boost_factor __read_mostly = 15000;
+#endif
static int watermark_scale_factor = 10;
/* movable_zone is the "real" zone pages in ZONE_MOVABLE are taken from */