linux-kernel - [v2 2/2] mm: khugepaged: avoid overriding min_free

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Message-Id: <1600204258-13683-2-git-send-email-vijayb@linux.microsoft.com>
Date:   Tue, 15 Sep 2020 14:10:58 -0700
From:   Vijay Balakrishna <vijayb@...ux.microsoft.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Song Liu <songliubraving@...com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Vijay Balakrishna <vijayb@...ux.microsoft.com>,
        Michal Hocko <mhocko@...e.com>,
        Allen Pais <apais@...rosoft.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: [v2 2/2] mm: khugepaged: avoid overriding min_free_kbytes set by user

set_recommended_min_free_kbytes need to honor min_free_kbytes set by the
user.  Post start-of-day THP enable or memory hotplug operations can
lose user specified min_free_kbytes, in particular when it is higher than
calculated recommended value.  Also modifying "recommended_min" variable
type to "int" from "unsigned long" to avoid undesired result noticed
during testing.  It is due to comparing "unsigned long" with "int" type.

Signed-off-by: Vijay Balakrishna <vijayb@...ux.microsoft.com>
Cc: stable@...r.kernel.org
Reviewed-by: Pavel Tatashin <pasha.tatashin@...een.com>
---
 mm/khugepaged.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 4f7107476a6f..b4b753ba411a 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -2253,7 +2253,7 @@ static void set_recommended_min_free_kbytes(void)
 {
 	struct zone *zone;
 	int nr_zones = 0;
-	unsigned long recommended_min;
+	int recommended_min;
 
 	for_each_populated_zone(zone) {
 		/*
@@ -2280,12 +2280,12 @@ static void set_recommended_min_free_kbytes(void)
 
 	/* don't ever allow to reserve more than 5% of the lowmem */
 	recommended_min = min(recommended_min,
-			      (unsigned long) nr_free_buffer_pages() / 20);
+			      (int) nr_free_buffer_pages() / 20);
 	recommended_min <<= (PAGE_SHIFT-10);
 
-	if (recommended_min > min_free_kbytes) {
+	if (recommended_min > user_min_free_kbytes) {
 		if (user_min_free_kbytes >= 0)
-			pr_info("raising min_free_kbytes from %d to %lu to help transparent hugepage allocations\n",
+			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;
-- 
2.28.0