From 419e140a80f0fbbb624f6ba918f986cd6b4e2f79 Mon Sep 17 00:00:00 2001
From: Suren Baghdasaryan <surenb@google.com>
Date: Fri, 14 Jan 2022 14:07:17 -0800
Subject: [PATCH] mm/pagealloc: sysctl: change watermark_scale_factor max limit
 to 30%

References: bnc#1189998 (PREEMPT_RT prerequisite backports)
Patch-mainline: v5.17-rc0
Git-commit: 39c65a94cd9661532be150e88f8b02f4a6844a35

For embedded systems with low total memory, having to run applications
with relatively large memory requirements, 10% max limitation for
watermark_scale_factor poses an issue of triggering direct reclaim every
time such application is started.  This results in slow application
startup times and bad end-user experience.

By increasing watermark_scale_factor max limit we allow vendors more
flexibility to choose the right level of kswapd aggressiveness for their
device and workload requirements.

Link: https://lkml.kernel.org/r/20211124193604.2758863-1-surenb@google.com
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Lukas Middendorf <kernel@tuxforce.de>
Cc: Antti Palosaari <crope@iki.fi>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Iurii Zaikin <yzaikin@google.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Zhang Yi <yi.zhang@huawei.com>
Cc: Fengfei Xi <xi.fengfei@h3c.com>
Cc: Mike Rapoport <rppt@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Mel Gorman <mgorman@suse.de>
---
 Documentation/admin-guide/sysctl/vm.rst | 2 +-
 kernel/sysctl.c                         | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst
index 5e795202111f..f4804ce37c58 100644
--- a/Documentation/admin-guide/sysctl/vm.rst
+++ b/Documentation/admin-guide/sysctl/vm.rst
@@ -948,7 +948,7 @@ how much memory needs to be free before kswapd goes back to sleep.
 
 The unit is in fractions of 10,000. The default value of 10 means the
 distances between watermarks are 0.1% of the available memory in the
-node/system. The maximum value is 1000, or 10% of memory.
+node/system. The maximum value is 3000, or 30% of memory.
 
 A high rate of threads entering direct reclaim (allocstall) or kswapd
 going to sleep prematurely (kswapd_low_wmark_hit_quickly) can indicate
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 083be6af29d7..2ab4edb6e450 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -122,6 +122,7 @@ static unsigned long long_max = LONG_MAX;
 static int one_hundred = 100;
 static int two_hundred = 200;
 static int one_thousand = 1000;
+static int three_thousand = 3000;
 #ifdef CONFIG_PRINTK
 static int ten_thousand = 10000;
 #endif
@@ -2959,7 +2960,7 @@ static struct ctl_table vm_table[] = {
 		.mode		= 0644,
 		.proc_handler	= watermark_scale_factor_sysctl_handler,
 		.extra1		= SYSCTL_ONE,
-		.extra2		= &one_thousand,
+		.extra2		= &three_thousand,
 	},
 	{
 		.procname	= "percpu_pagelist_high_fraction",