From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f71.google.com (mail-ed1-f71.google.com [209.85.208.71]) by kanga.kvack.org (Postfix) with ESMTP id 394656B08D7 for ; Fri, 16 Nov 2018 04:57:22 -0500 (EST) Received: by mail-ed1-f71.google.com with SMTP id z10so5887550edz.15 for ; Fri, 16 Nov 2018 01:57:22 -0800 (PST) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id cb13-v6si1326282ejb.102.2018.11.16.01.57.20 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 16 Nov 2018 01:57:20 -0800 (PST) Date: Fri, 16 Nov 2018 10:57:20 +0100 From: Michal Hocko Subject: Re: [PATCH] mm: use managed_zone() for more exact check in zone iteration Message-ID: <20181116095720.GE14706@dhcp22.suse.cz> References: <20181114235040.36180-1-richard.weiyang@gmail.com> <20181115133735.bb0313ec9293c415d08be550@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181115133735.bb0313ec9293c415d08be550@linux-foundation.org> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Wei Yang , linux-mm@kvack.org, linux-kernel@vger.kernel.org On Thu 15-11-18 13:37:35, Andrew Morton wrote: [...] > Worse, the situations in which managed_zone() != populated_zone() are > rare(?), so it will take a long time for problems to be discovered, I > expect. We would basically have to deplete the whole zone by the bootmem allocator or pull out all pages from the page allocator. E.g. memory hotplug decreases both managed and present counters. I am actually not sure that is 100% correct (put on my TODO list to check). There is no consistency in that regards. That being said, I will review the patch (today hopefully) but fundamentally most users should indeed care about managed pages when iterating zones with memory. There should be a good reason why they might want to look at reserved pages. -- Michal Hocko SUSE Labs