linux-kernel - Re: [RFC] mm: show message when updating min_free

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Message-ID: <20140103033303.GB4106@localhost.localdomain>
Date:	Fri, 3 Jan 2014 11:33:03 +0800
From:	Han Pingtian <hanpt@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	Dave Hansen <dave.hansen@...el.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Mel Gorman <mgorman@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	Michal Hocko <mhocko@...e.cz>
Subject: Re: [RFC] mm: show message when updating min_free_kbytes in thp

On Thu, Jan 02, 2014 at 10:05:21AM -0800, Dave Hansen wrote:
> On 12/31/2013 04:29 PM, Han Pingtian wrote:
> > min_free_kbytes may be updated during thp's initialization. Sometimes,
> > this will change the value being set by user. Showing message will
> > clarify this confusion.
> ...
> > -	if (recommended_min > min_free_kbytes)
> > +	if (recommended_min > min_free_kbytes) {
> >  		min_free_kbytes = recommended_min;
> > +		pr_info("min_free_kbytes is updated to %d by enabling transparent hugepage.\n",
> > +			min_free_kbytes);
> > +	}
> 
> "updated" doesn't tell us much.  It's also kinda nasty that if we enable
> then disable THP, we end up with an elevated min_free_kbytes.  Maybe we
> should at least put something in that tells the user how to get back
> where they were if they care:
> 
> "raising min_free_kbytes from %d to %d to help transparent hugepage
> allocations"
> 
Thanks. I have updated it according to your suggestion.


>From f9902b16ff0c326349e72eca9facef2c98f8595d Mon Sep 17 00:00:00 2001
From: Han Pingtian <hanpt@...ux.vnet.ibm.com>
Date: Fri, 3 Jan 2014 11:10:49 +0800
Subject: [PATCH] mm: show message when raising min_free_kbytes in THP

min_free_kbytes may be raised during THP's initialization. Sometimes,
this will change the value being set by user. Showing message will
clarify this confusion.

Showing the old value of min_free_kbytes according to Dave Hansen's
suggestion. This will give user the chance to restore old value of
min_free_kbytes.

Signed-off-by: Han Pingtian <hanpt@...ux.vnet.ibm.com>
---
 mm/huge_memory.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 7de1bf8..1f0356d 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -130,8 +130,11 @@ static int set_recommended_min_free_kbytes(void)
 			      (unsigned long) nr_free_buffer_pages() / 20);
 	recommended_min <<= (PAGE_SHIFT-10);
 
-	if (recommended_min > min_free_kbytes)
+	if (recommended_min > min_free_kbytes) {
+		pr_info("raising min_free_kbytes from %d to %d to help transparent hugepage allocations\n",
+			min_free_kbytes, recommended_min);
 		min_free_kbytes = recommended_min;
+	}
 	setup_per_zone_wmarks();
 	return 0;
 }
-- 
1.7.7.6

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