From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f72.google.com (mail-ed1-f72.google.com [209.85.208.72]) by kanga.kvack.org (Postfix) with ESMTP id 1ACE36B0003 for ; Thu, 18 Oct 2018 10:10:13 -0400 (EDT) Received: by mail-ed1-f72.google.com with SMTP id c26-v6so18488950eda.7 for ; Thu, 18 Oct 2018 07:10:13 -0700 (PDT) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id v50-v6sor15933327edm.6.2018.10.18.07.10.11 for (Google Transport Security); Thu, 18 Oct 2018 07:10:11 -0700 (PDT) Date: Thu, 18 Oct 2018 14:10:08 +0000 From: Wei Yang Subject: Re: [PATCH] mm: get pfn by page_to_pfn() instead of save in page->private Message-ID: <20181018141008.lcyttmp7bb42uigi@master> Reply-To: Wei Yang References: <20181018130429.37837-1-richard.weiyang@gmail.com> <20181018131504.GC18839@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181018131504.GC18839@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Wei Yang , akpm@linux-foundation.org, mgorman@techsingularity.net, linux-mm@kvack.org On Thu, Oct 18, 2018 at 03:15:04PM +0200, Michal Hocko wrote: >On Thu 18-10-18 21:04:29, Wei Yang wrote: >> This is not necessary to save the pfn to page->private. >> >> The pfn could be retrieved by page_to_pfn() directly. > >Yes it can, but a cursory look at the commit which has introduced this >suggests that this is a micro-optimization. Mel would know more of >course. There are some memory models where page_to_pfn is close to free. > >If that is the case I am not really sure it is measurable or worth it. >In any case any change to this code should have a proper justification. >In other words, is this change really needed? Does it help in any >aspect? Possibly readability? The only thing I can guess from this >changelog is that you read the code and stumble over this. If that is >the case I would recommend asking author for the motivation and >potentially add a comment to explain it better rather than shoot a patch >rightaway. > Your are right. I am really willing to understand why we want to use this mechanisum. So the correct procedure is to send a mail to the mail list to query the reason?