linux-kernel - [PATCH] mm: align up min_free

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Date:   Sun, 9 Jun 2019 17:10:28 +0800
From:   ChenGang <cg.chen@...wei.com>
To:     <akpm@...ux-foundation.org>, <mhocko@...e.com>, <vbabka@...e.cz>,
        <osalvador@...e.de>, <pavel.tatashin@...rosoft.com>
CC:     <mgorman@...hsingularity.net>, <rppt@...ux.ibm.com>,
        <richard.weiyang@...il.com>, <alexander.h.duyck@...ux.intel.com>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        ChenGang <cg.chen@...wei.com>
Subject: [PATCH] mm: align up min_free_kbytes to multipy of 4

Usually the value of min_free_kbytes is multiply of 4,
and in this case ,the right shift is ok.
But if it's not, the right-shifting operation will lose the low 2 bits,
and this cause kernel don't reserve enough memory.
So it's necessary to align the value of min_free_kbytes to multiply of 4.
For example, if min_free_kbytes is 64, then should keep 16 pages,
but if min_free_kbytes is 65 or 66, then should keep 17 pages.

Signed-off-by: ChenGang <cg.chen@...wei.com>
---
 mm/page_alloc.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d66bc8a..1baeeba 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -7611,7 +7611,8 @@ static void setup_per_zone_lowmem_reserve(void)
 
 static void __setup_per_zone_wmarks(void)
 {
-	unsigned long pages_min = min_free_kbytes >> (PAGE_SHIFT - 10);
+	unsigned long pages_min =
+		(PAGE_ALIGN(min_free_kbytes * 1024) / 1024) >> (PAGE_SHIFT - 10);
 	unsigned long lowmem_pages = 0;
 	struct zone *zone;
 	unsigned long flags;
-- 
1.8.5.6