From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f70.google.com (mail-pa0-f70.google.com [209.85.220.70]) by kanga.kvack.org (Postfix) with ESMTP id 0749C6B0069 for ; Fri, 2 Sep 2016 16:30:18 -0400 (EDT) Received: by mail-pa0-f70.google.com with SMTP id hi6so52879014pac.0 for ; Fri, 02 Sep 2016 13:30:17 -0700 (PDT) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTPS id s70si13157162pfa.89.2016.09.02.13.30.17 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 02 Sep 2016 13:30:17 -0700 (PDT) Date: Fri, 2 Sep 2016 13:30:16 -0700 From: Andrew Morton Subject: Re: [PATCH -v2 01/10] swap: Change SWAPFILE_CLUSTER to 512 Message-Id: <20160902133016.0a150c880174fa97f161912f@linux-foundation.org> In-Reply-To: <87h99zdxwm.fsf@yhuang-mobile.sh.intel.com> References: <1472743023-4116-1-git-send-email-ying.huang@intel.com> <1472743023-4116-2-git-send-email-ying.huang@intel.com> <20160901142246.631fe47a558bb7522f73c034@linux-foundation.org> <87h99zdxwm.fsf@yhuang-mobile.sh.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: "Huang, Ying" Cc: tim.c.chen@intel.com, dave.hansen@intel.com, andi.kleen@intel.com, aaron.lu@intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hugh Dickins , Shaohua Li , Minchan Kim , Rik van Riel On Thu, 01 Sep 2016 16:04:57 -0700 "Huang\, Ying" wrote: > >> } > >> > >> -#define SWAPFILE_CLUSTER 256 > >> +#define SWAPFILE_CLUSTER 512 > >> #define LATENCY_LIMIT 256 > >> > > > > What happens to architectures which have different HPAGE_SIZE and/or > > PAGE_SIZE? > > For the architecture with HPAGE_SIZE / PAGE_SIZE == 512 (for example > x86_64), the huge page swap optimizing will be turned on. For other > architectures, it will be turned off as before. > > This mostly because I don't know whether it is a good idea to turn on > THP swap optimizing for the architectures other than x86_64. For > example, it appears that the huge page size is 8M (1<<23) on SPARC. But > I don't know whether 8M is too big for a swap cluster. And it appears > that the huge page size could be as large as 512M on MIPS. This doesn't sounds very organized. If some architecture with some config happens to have HPAGE_SIZE / PAGE_SIZE == 512 then the feature will be turned on; otherwise it will be turned off. Nobody will even notice that it happened. Would it not be better to do #ifdef CONFIG_SOMETHING #define SWAPFILE_CLUSTER (HPAGE_SIZE / PAGE_SIZE) #else #define SWAPFILE_CLUSTER 256 #endif and, by using CONFIG_SOMETHING in the other appropriate places, enable the feature in the usual fashion? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org