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=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 28650C433E0 for ; Mon, 22 Mar 2021 08:31:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D40F06196C for ; Mon, 22 Mar 2021 08:31:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229647AbhCVIaz (ORCPT ); Mon, 22 Mar 2021 04:30:55 -0400 Received: from outbound-smtp34.blacknight.com ([46.22.139.253]:49739 "EHLO outbound-smtp34.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229665AbhCVIan (ORCPT ); Mon, 22 Mar 2021 04:30:43 -0400 Received: from mail.blacknight.com (pemlinmail04.blacknight.ie [81.17.254.17]) by outbound-smtp34.blacknight.com (Postfix) with ESMTPS id 5D946272A for ; Mon, 22 Mar 2021 08:30:41 +0000 (GMT) Received: (qmail 12857 invoked from network); 22 Mar 2021 08:30:41 -0000 Received: from unknown (HELO techsingularity.net) (mgorman@techsingularity.net@[84.203.22.4]) by 81.17.254.9 with ESMTPSA (AES256-SHA encrypted, authenticated); 22 Mar 2021 08:30:41 -0000 Date: Mon, 22 Mar 2021 08:30:39 +0000 From: Mel Gorman To: Vlastimil Babka Cc: Andrew Morton , Chuck Lever , Jesper Dangaard Brouer , Christoph Hellwig , Alexander Duyck , Matthew Wilcox , LKML , Linux-Net , Linux-MM , Linux-NFS Subject: Re: [PATCH 3/7] mm/page_alloc: Add a bulk page allocator Message-ID: <20210322083039.GD3697@techsingularity.net> References: <20210312154331.32229-1-mgorman@techsingularity.net> <20210312154331.32229-4-mgorman@techsingularity.net> <7c520bbb-efd7-7cad-95df-610000832a67@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <7c520bbb-efd7-7cad-95df-610000832a67@suse.cz> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Mar 19, 2021 at 07:18:32PM +0100, Vlastimil Babka wrote: > On 3/12/21 4:43 PM, Mel Gorman wrote: > > This patch adds a new page allocator interface via alloc_pages_bulk, > > and __alloc_pages_bulk_nodemask. A caller requests a number of pages > > to be allocated and added to a list. They can be freed in bulk using > > free_pages_bulk(). > > > > The API is not guaranteed to return the requested number of pages and > > may fail if the preferred allocation zone has limited free memory, the > > cpuset changes during the allocation or page debugging decides to fail > > an allocation. It's up to the caller to request more pages in batch > > if necessary. > > > > Note that this implementation is not very efficient and could be improved > > but it would require refactoring. The intent is to make it available early > > to determine what semantics are required by different callers. Once the > > full semantics are nailed down, it can be refactored. > > > > Signed-off-by: Mel Gorman > > Acked-by: Vlastimil Babka > > Although maybe premature, if it changes significantly due to the users' > performance feedback, let's see :) > Indeed. The next version will have no users so that Jesper and Chuck can check if an array-based or LRU based version is better. There were also bugs such as broken accounting of stats that had to be fixed which increases overhead. > Some nits below: > > ... > > > @@ -4963,6 +4978,107 @@ static inline bool prepare_alloc_pages(gfp_t gfp, unsigned int order, > > return true; > > } > > > > +/* > > + * This is a batched version of the page allocator that attempts to > > + * allocate nr_pages quickly from the preferred zone and add them to list. > > + * > > + * Returns the number of pages allocated. > > + */ > > +int __alloc_pages_bulk(gfp_t gfp, int preferred_nid, > > + nodemask_t *nodemask, int nr_pages, > > + struct list_head *alloc_list) > > +{ > > + struct page *page; > > + unsigned long flags; > > + struct zone *zone; > > + struct zoneref *z; > > + struct per_cpu_pages *pcp; > > + struct list_head *pcp_list; > > + struct alloc_context ac; > > + gfp_t alloc_gfp; > > + unsigned int alloc_flags; > > + int allocated = 0; > > + > > + if (WARN_ON_ONCE(nr_pages <= 0)) > > + return 0; > > + > > + if (nr_pages == 1) > > + goto failed; > > + > > + /* May set ALLOC_NOFRAGMENT, fragmentation will return 1 page. */ > > + if (!prepare_alloc_pages(gfp, 0, preferred_nid, nodemask, &ac, > > + &alloc_gfp, &alloc_flags)) > > Unusual identation here. > Fixed > > + return 0; > > + gfp = alloc_gfp; > > + > > + /* Find an allowed local zone that meets the high watermark. */ > > + for_each_zone_zonelist_nodemask(zone, z, ac.zonelist, ac.highest_zoneidx, ac.nodemask) { > > + unsigned long mark; > > + > > + if (cpusets_enabled() && (alloc_flags & ALLOC_CPUSET) && > > + !__cpuset_zone_allowed(zone, gfp)) { > > + continue; > > + } > > + > > + if (nr_online_nodes > 1 && zone != ac.preferred_zoneref->zone && > > + zone_to_nid(zone) != zone_to_nid(ac.preferred_zoneref->zone)) { > > + goto failed; > > + } > > + > > + mark = wmark_pages(zone, alloc_flags & ALLOC_WMARK_MASK) + nr_pages; > > + if (zone_watermark_fast(zone, 0, mark, > > + zonelist_zone_idx(ac.preferred_zoneref), > > + alloc_flags, gfp)) { > > + break; > > + } > > + } > > + if (!zone) > > + return 0; > > Why not also "goto failed;" here? Good question. When first written, it was because the zone search for the normal allocator was almost certainly going to fail to find a zone and it was expected that callers would prefer to fail fast over blocking. Now we know that sunrpc can sleep on a failing allocation and it would be better to enter the single page allocator and reclaim pages instead of "sleep and hope for the best". -- Mel Gorman SUSE Labs