From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9B1FEC433B4 for ; Wed, 21 Apr 2021 08:00:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 624B761437 for ; Wed, 21 Apr 2021 08:00:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237534AbhDUIBP (ORCPT ); Wed, 21 Apr 2021 04:01:15 -0400 Received: from mx2.suse.de ([195.135.220.15]:49556 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235510AbhDUIBM (ORCPT ); Wed, 21 Apr 2021 04:01:12 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 303F8B127; Wed, 21 Apr 2021 08:00:39 +0000 (UTC) Date: Wed, 21 Apr 2021 10:00:36 +0200 From: Oscar Salvador To: Michal Hocko Cc: Andrew Morton , David Hildenbrand , Anshuman Khandual , Pavel Tatashin , Vlastimil Babka , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v9 3/8] mm,memory_hotplug: Factor out adjusting present pages into adjust_present_page_count() Message-ID: <20210421080036.GC22456@linux> References: <20210416112411.9826-1-osalvador@suse.de> <20210416112411.9826-4-osalvador@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 20, 2021 at 11:45:55AM +0200, Michal Hocko wrote: > On Fri 16-04-21 13:24:06, Oscar Salvador wrote: > > From: David Hildenbrand > > > > Let's have a single place (inspired by adjust_managed_page_count()) where > > we adjust present pages. > > In contrast to adjust_managed_page_count(), only memory onlining/offlining > > is allowed to modify the number of present pages. > > > > Signed-off-by: David Hildenbrand > > Signed-off-by: Oscar Salvador > > Reviewed-by: Oscar Salvador > > Not sure self review counts ;) Uhm, the original author is David, I just added my signed-off-by as a deliverer. I thought that in that case was ok to stick my Reviewed-by. Or maybe my signed-off-by carries that implicitly. > Acked-by: Michal Hocko > > Btw. I strongly suspect the resize lock is quite pointless here. > Something for a follow up patch. What makes you think that? I have been thinking about this, let us ignore this patch for a moment. If I poked the code correctly, node_size_lock is taken in: remove_pfn_range_from_zone() move_pfn_range_to_zone() both of them handling {zone,node}->spanned_pages Then we take it in {offline,online}_pages() for {zone,node}->present_pages. The other places where we take it are __init functions, so not of interest. Given that {offline,online}_pages() is serialized by the memory_hotplug lock, I would say that {node,zone}->{spanned,present}_pages is, at any time, stable? So, no need for the lock even without considering this patch? Now, getting back to this patch. adjust_present_page_count() will be called from memory_block_online(), which is not holding the memory_hotplug lock yet. But, we only fiddle with present pages out of {online,offline}_pages() if we have vmemmap pages, and since that operates on the same memory block, its lock should serialize that. I think I went down a rabbit hole, I am slightly confused now. -- Oscar Salvador SUSE L3