From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757812AbcIVQag (ORCPT ); Thu, 22 Sep 2016 12:30:36 -0400 Received: from sender153-mail.zoho.com ([74.201.84.153]:25348 "EHLO sender153-mail.zoho.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754440AbcIVQae (ORCPT ); Thu, 22 Sep 2016 12:30:34 -0400 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=zapps768; d=zoho.com; h=subject:to:references:cc:from:message-id:date:user-agent:mime-version:in-reply-to:content-type; b=e8NPHcdfFYT2fg5n4B/nrSWBj2bhrt2MIqwIVd2LXmkYc6+sNgpZxUiP8SGmi4aZNmNY+r+Qup2q A/++LF6nEA4r1WspuUbzC26TOVwTUh87V3NS6mhfzqW3oiRKJW2h Subject: Re: [PATCH 3/5] mm/vmalloc.c: correct lazy_max_pages() return value To: Michal Hocko , npiggin@suse.de, npiggin@gmail.com References: <57E20C49.8010304@zoho.com> <3ef46c24-769d-701a-938b-826f4249bf0b@zoho.com> <57E3304E.4060401@zoho.com> <20160922123736.GA11204@dhcp22.suse.cz> Cc: zijun_hu@htc.com, David Rientjes , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , tj@kernel.org, mingo@kernel.org, iamjoonsoo.kim@lge.com, mgorman@techsingularity.net From: zijun_hu Message-ID: <7671e782-b58f-7c41-b132-c7ebbcf61b99@zoho.com> Date: Fri, 23 Sep 2016 00:30:20 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0 MIME-Version: 1.0 In-Reply-To: <20160922123736.GA11204@dhcp22.suse.cz> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2016/9/22 20:37, Michal Hocko wrote: > On Thu 22-09-16 09:13:50, zijun_hu wrote: >> On 09/22/2016 08:35 AM, David Rientjes wrote: > [...] >>> The intent is as it is implemented; with your change, lazy_max_pages() is >>> potentially increased depending on the number of online cpus. This is >>> only a heuristic, changing it would need justification on why the new >>> value is better. It is opposite to what the comment says: "to be >>> conservative and not introduce a big latency on huge systems, so go with >>> a less aggressive log scale." NACK to the patch. >>> >> my change potentially make lazy_max_pages() decreased not increased, i seems >> conform with the comment >> >> if the number of online CPUs is not power of 2, both have no any difference >> otherwise, my change remain power of 2 value, and the original code rounds up >> to next power of 2 value, for instance >> >> my change : (32, 64] -> 64 >> 32 -> 32, 64 -> 64 >> the original code: [32, 63) -> 64 >> 32 -> 64, 64 -> 128 > > You still completely failed to explain _why_ this is an improvement/fix > or why it matters. This all should be in the changelog. > Hi npiggin, could you give some comments for this patch since lazy_max_pages() is introduced by you my patch is based on the difference between fls() and get_count_order() mainly the difference between fls() and get_count_order() will be shown below more MM experts maybe help to decide which is more suitable if parameter > 1, both have different return value only when parameter is power of two, for example fls(32) = 6 VS get_count_order(32) = 5 fls(33) = 6 VS get_count_order(33) = 6 fls(63) = 6 VS get_count_order(63) = 6 fls(64) = 7 VS get_count_order(64) = 6 @@ -594,7 +594,9 @@ static unsigned long lazy_max_pages(void) { unsigned int log; - log = fls(num_online_cpus()); + log = num_online_cpus(); + if (log > 1) + log = (unsigned int)get_count_order(log); return log * (32UL * 1024 * 1024 / PAGE_SIZE); }