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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Sultan Alsawaf <sultan@kerneltoast.com>
Date: Sat, 28 Mar 2020 13:06:28 -0700
Subject: [PATCH] ZEN: 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>
---
mm/page_alloc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index b5b14b78c4fd4844cb071022570fd4b7e6959eb2..d6fc4723c4e9137a3bf8193fcbad1bb23f041c43 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -342,7 +342,7 @@ compound_page_dtor * const compound_page_dtors[NR_COMPOUND_DTORS] = {
int min_free_kbytes = 1024;
int user_min_free_kbytes = -1;
-int watermark_boost_factor __read_mostly = 15000;
+int watermark_boost_factor __read_mostly;
int watermark_scale_factor = 10;
static unsigned long nr_kernel_pages __initdata;
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