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[45.249.212.187]) by mx.google.com with ESMTPS id s20si7652122iom.2.2019.06.11.05.17.14 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 11 Jun 2019 05:17:15 -0700 (PDT) Received-SPF: pass (google.com: domain of cg.chen@huawei.com designates 45.249.212.187 as permitted sender) client-ip=45.249.212.187; Authentication-Results: mx.google.com; spf=pass (google.com: domain of cg.chen@huawei.com designates 45.249.212.187 as permitted sender) smtp.mailfrom=cg.chen@huawei.com Received: from dggemi403-hub.china.huawei.com (unknown [172.30.72.56]) by Forcepoint Email with ESMTP id 542341CB09A22907BC29; Tue, 11 Jun 2019 20:16:42 +0800 (CST) Received: from DGGEMI529-MBS.china.huawei.com ([169.254.5.79]) by dggemi403-hub.china.huawei.com ([10.3.17.136]) with mapi id 14.03.0415.000; Tue, 11 Jun 2019 20:16:35 +0800 From: "Chengang (L)" To: Michal Hocko CC: "akpm@linux-foundation.org" , "vbabka@suse.cz" , "osalvador@suse.de" , "pavel.tatashin@microsoft.com" , "mgorman@techsingularity.net" , "rppt@linux.ibm.com" , "richard.weiyang@gmail.com" , "alexander.h.duyck@linux.intel.com" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] mm: align up min_free_kbytes to multipy of 4 Thread-Topic: [PATCH] mm: align up min_free_kbytes to multipy of 4 Thread-Index: AdUgTpdGfX4K+yczTYe6f6nhJDDS/w== Date: Tue, 11 Jun 2019 12:16:35 +0000 Message-ID: Accept-Language: en-US Content-Language: zh-CN X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.74.216.69] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-CFilter-Loop: Reflected X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Hi Michal >On Sun 09-06-19 17:10:28, ChenGang wrote: >> Usually the value of min_free_kbytes is multiply of 4, and in this=20 >> case ,the right shift is ok. >> But if it's not, the right-shifting operation will lose the low 2=20 >> 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=20 >> if min_free_kbytes is 65 or 66, then should keep 17 pages. >Could you describe the actual problem? Do we ever generate min_free_kbytes= that would lead to unexpected reserves or is this trying to compensate for= those values being configured from the userspace? If later why do we care = at all? >Have you seen this to be an actual problem or is this mostly motivated by = the code reading? I haven't seen an actual problem, and it's motivated by code reading. User= s can configure this value through interface /proc/sys/vm/min_free_kbytes, = so I think a bit precious is better. >> Signed-off-by: ChenGang >> --- >> mm/page_alloc.c | 3 ++- >> 1 file changed, 2 insertions(+), 1 deletion(-) >>=20 >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c index d66bc8a..1baeeba=20 >> 100644 >> --- a/mm/page_alloc.c >> +++ b/mm/page_alloc.c >> @@ -7611,7 +7611,8 @@ static void setup_per_zone_lowmem_reserve(void) >> =20 >> static void __setup_per_zone_wmarks(void) { >> - unsigned long pages_min =3D min_free_kbytes >> (PAGE_SHIFT - 10); >> + unsigned long pages_min =3D >> + (PAGE_ALIGN(min_free_kbytes * 1024) / 1024) >> (PAGE_SHIFT - 10); >> unsigned long lowmem_pages =3D 0; >> struct zone *zone; >> unsigned long flags; >> -- >> 1.8.5.6 >>=20 >--=20 >Michal Hocko >SUSE Labs