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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D6E29C433EF for ; Thu, 21 Apr 2022 08:38:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1386791AbiDUIlJ (ORCPT ); Thu, 21 Apr 2022 04:41:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53484 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238523AbiDUIlI (ORCPT ); Thu, 21 Apr 2022 04:41:08 -0400 Received: from outbound-smtp01.blacknight.com (outbound-smtp01.blacknight.com [81.17.249.7]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D085ABC00 for ; Thu, 21 Apr 2022 01:38:18 -0700 (PDT) Received: from mail.blacknight.com (pemlinmail04.blacknight.ie [81.17.254.17]) by outbound-smtp01.blacknight.com (Postfix) with ESMTPS id 34520C4B26 for ; Thu, 21 Apr 2022 09:38:17 +0100 (IST) Received: (qmail 16182 invoked from network); 21 Apr 2022 08:38:17 -0000 Received: from unknown (HELO techsingularity.net) (mgorman@techsingularity.net@[84.203.198.246]) by 81.17.254.9 with ESMTPSA (AES256-SHA encrypted, authenticated); 21 Apr 2022 08:38:16 -0000 Date: Thu, 21 Apr 2022 09:38:11 +0100 From: Mel Gorman To: Matthew Wilcox Cc: Nicolas Saenz Julienne , Marcelo Tosatti , Vlastimil Babka , Michal Hocko , LKML , Linux-MM Subject: Re: [PATCH 1/6] mm/page_alloc: Add page->buddy_list and page->pcp_list Message-ID: <20220421083811.GA4105@techsingularity.net> References: <20220420095906.27349-1-mgorman@techsingularity.net> <20220420095906.27349-2-mgorman@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 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 Wed, Apr 20, 2022 at 09:43:05PM +0100, Matthew Wilcox wrote: > On Wed, Apr 20, 2022 at 10:59:01AM +0100, Mel Gorman wrote: > > The page allocator uses page->lru for storing pages on either buddy or > > PCP lists. Create page->buddy_list and page->pcp_list as a union with > > page->lru. This is simply to clarify what type of list a page is on > > in the page allocator. > > Hi Mel, > > No objection to this change, and I certainly don't want to hold up > fixing this (or any other) problem in the page allocator. Minimally, I think the patch makes it easier to implement your suggestion and it can happen before or after the rest of the series. > I would > like to talk about splitting out free page management from struct page. > Maybe you'd like to discuss that in person at LSFMM, but a quick > sketch of a data structure might look like ... > Unfortunately, I am unable to attend LSF/MM (or any other conference) physically but I have no objection to splitting this out as a separate structure. I assume the basis for the change would be for type checking. > struct free_mem { > unsigned long __page_flags; page->flags, ok > union { > struct list_head buddy_list; > struct list_head pcp_list; > }; page->lru, ok > unsigned long __rsvd4; page->mapping, we need that > unsigned long pcp_migratetype_and_order; page->index, ok but more on this later > unsigned long buddy_order; page->private, ok. > unsigned int __page_type; page->_mapcount, we need that too. > atomic_t _refcount; page->_refcount, ok. > }; > > Am I missing anything there? > s/__page_flags/flags/ The allocator checks and modifies these bits so it has awareness of page->flags s/__rsvd4/mapping/ The mapping is checked for debugging and the allocator is responsible for clearing page->mapping s/pcp_migratetype_and_order/pcp_migratetype/ Commit 8b10b465d0e1 ("mm/page_alloc: free pages in a single pass during bulk free") removed the migratetype and order stuffing in page->index. The order is inferred from the array index via order_to_pindex and pindex_to_order but migratetype is still stored in page->index by set_pcppage_migratetype s/__page_type/_mapcount/ because _mapcount if checked for debugging memcg_data needs to be accessible for debugging checks _last_cpupid needs to be accessible as it's reset during prepare via page_cpupid_reset_last. Rather than putting in a dummy field for virtual, maybe virtual can move. > (Would you like to use separate types for pcp and buddy? That might be > overkill, or it might help keep the different stages of "free" memory > separate from each other) I think it's overkill because there is too much overlap between a PCP page and buddy page due to page checks and preparation. The distinguishing factor between a free pcp page and free buddy page is the PageBuddy bit. -- Mel Gorman SUSE Labs