Re: [RFC] mm: Honor min_free_kbytes set by user

[Michal Hocko <mhocko@suse.cz>]

On Thu 04-07-13 18:16:41, Michal Hocko wrote:
> On Thu 04-07-13 09:10:39, Joe Perches wrote:
> > On Thu, 2013-07-04 at 18:07 +0200, Michal Hocko wrote:
> > > A warning is printed when the new value is ignored.
> > 
> > []
> > 
> > > +		printk(KERN_WARNING "min_free_kbytes is not updated to %d"
> > > +				"because user defined value %d is preferred\n",
> > > +				new_min_free_kbytes, user_min_free_kbytes);
> > 
> > Please use pr_warn and coalesce the format.
> 
> Sure can do that. mm/page_alloc.c doesn't seem to be unified in that
> regards (44 printks and only 4 pr_<foo>) so I used printk.
> 
> > You'd've noticed a missing space between %d and because.
> 
> True
> 

Checkpatch fixes
---
>From 5f089c0b2a57ff6c08710ac9698d65aede06079f Mon Sep 17 00:00:00 2001
From: Michal Hocko <mhocko@suse.cz>
Date: Thu, 4 Jul 2013 17:15:54 +0200
Subject: [PATCH] mm: Honor min_free_kbytes set by user

min_free_kbytes is updated during memory hotplug (by init_per_zone_wmark_min)
currently which is right thing to do in most cases but this could be
unexpected if admin increased the value to prevent from allocation
failures and the new min_free_kbytes would be decreased as a result of
memory hotadd.

This patch saves the user defined value and allows updating
min_free_kbytes only if it is higher than the saved one.

A warning is printed when the new value is ignored.

Signed-off-by: Michal Hocko <mhocko@suse.cz>
---
 mm/page_alloc.c | 24 +++++++++++++++++-------
 1 file changed, 17 insertions(+), 7 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 22c528e..9c011fc 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -204,6 +204,7 @@ static char * const zone_names[MAX_NR_ZONES] = {
 };
 
 int min_free_kbytes = 1024;
+int user_min_free_kbytes;
 
 static unsigned long __meminitdata nr_kernel_pages;
 static unsigned long __meminitdata nr_all_pages;
@@ -5592,14 +5593,21 @@ static void __meminit setup_per_zone_inactive_ratio(void)
 int __meminit init_per_zone_wmark_min(void)
 {
 	unsigned long lowmem_kbytes;
+	int new_min_free_kbytes;
 
 	lowmem_kbytes = nr_free_buffer_pages() * (PAGE_SIZE >> 10);
-
-	min_free_kbytes = int_sqrt(lowmem_kbytes * 16);
-	if (min_free_kbytes < 128)
-		min_free_kbytes = 128;
-	if (min_free_kbytes > 65536)
-		min_free_kbytes = 65536;
+	new_min_free_kbytes = int_sqrt(lowmem_kbytes * 16);
+
+	if (new_min_free_kbytes > user_min_free_kbytes) {
+		min_free_kbytes = new_min_free_kbytes;
+		if (min_free_kbytes < 128)
+			min_free_kbytes = 128;
+		if (min_free_kbytes > 65536)
+			min_free_kbytes = 65536;
+	} else {
+		pr_warn("min_free_kbytes is not updated to %d because user defined value %d is preferred\n",
+				new_min_free_kbytes, user_min_free_kbytes);
+	}
 	setup_per_zone_wmarks();
 	refresh_zone_stat_thresholds();
 	setup_per_zone_lowmem_reserve();
@@ -5617,8 +5625,10 @@ int min_free_kbytes_sysctl_handler(ctl_table *table, int write,
 	void __user *buffer, size_t *length, loff_t *ppos)
 {
 	proc_dointvec(table, write, buffer, length, ppos);
-	if (write)
+	if (write) {
+		user_min_free_kbytes = min_free_kbytes;
 		setup_per_zone_wmarks();
+	}
 	return 0;
 }
 
-- 
1.8.3.1

-- 
Michal Hocko
SUSE Labs