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=-18.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT 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 807CCC47087 for ; Fri, 28 May 2021 07:52:05 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 37ACC613AB for ; Fri, 28 May 2021 07:52:05 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 37ACC613AB Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 85EF96B006C; Fri, 28 May 2021 03:52:04 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 80C6F6B006E; Fri, 28 May 2021 03:52:04 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 686B88D0001; Fri, 28 May 2021 03:52:04 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0053.hostedemail.com [216.40.44.53]) by kanga.kvack.org (Postfix) with ESMTP id 347626B006C for ; Fri, 28 May 2021 03:52:04 -0400 (EDT) Received: from smtpin19.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 43647180F9855 for ; Fri, 28 May 2021 07:52:02 +0000 (UTC) X-FDA: 78189871284.19.26AEE76 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by imf30.hostedemail.com (Postfix) with ESMTP id 83FE9E00025B for ; Fri, 28 May 2021 07:51:55 +0000 (UTC) Received: from imap.suse.de (imap-alt.suse-dmz.suse.de [192.168.254.47]) (using TLSv1.2 with cipher ECDHE-ECDSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id A2501218B3; Fri, 28 May 2021 07:52:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1622188320; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc; bh=ejLAcKBj1HyRFBYRWQnOnTKNhRyWpmjRKdoHUgHMJok=; b=f9IDGY3BeU24qZ062IbdDfIBaMHHTwjCNwmqWtX63p5JHTyXbFUQUtEhmiyjVCt1hJ7mMk OlA42usaLiMTpAPtt17RF0Zvxn7aqVHMQodUxBCjyE7Kc1ajUYQ5S6kgI4LZ7btr/j/p38 EjxFaNVfNBoUANFwbrgUOKHtZM2ka/c= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1622188320; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc; bh=ejLAcKBj1HyRFBYRWQnOnTKNhRyWpmjRKdoHUgHMJok=; b=zPIJPgNdhx/aM2DNwYygCG9WHZYaa0X4JQbYBSJZMYDW0vDkCQYiJYP6bZQJ5HcdiQDHh9 vH1i6zGYMmcj0aCA== Received: from director2.suse.de (director2.suse-dmz.suse.de [192.168.254.72]) by imap.suse.de (Postfix) with ESMTPSA id CD1EF11A98; Fri, 28 May 2021 07:51:59 +0000 (UTC) From: Oscar Salvador To: Andrew Morton Cc: David Hildenbrand , Michal Hocko , Anshuman Khandual , Vlastimil Babka , Pavel Tatashin , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Oscar Salvador Subject: [PATCH RFC] mm,memory_hotplug: Drop unneeded locking Date: Fri, 28 May 2021 09:51:55 +0200 Message-Id: <20210528075155.358-1-osalvador@suse.de> X-Mailer: git-send-email 2.13.7 Authentication-Results: imf30.hostedemail.com; dkim=pass header.d=suse.de header.s=susede2_rsa header.b=f9IDGY3B; dkim=pass header.d=suse.de header.s=susede2_ed25519 header.b=zPIJPgNd; spf=pass (imf30.hostedemail.com: domain of osalvador@suse.de designates 195.135.220.28 as permitted sender) smtp.mailfrom=osalvador@suse.de; dmarc=none X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 83FE9E00025B X-Stat-Signature: i9ptdu3sjkxmnm793aci1k1gybjg78r8 X-HE-Tag: 1622188315-486378 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Currently, memory-hotplug code takes zone's span_writelock and pgdat's resize_lock when resizing the node/zone's spanned pages via {move_pfn_range_to_zone(),remove_pfn_range_from_zone()} and when resizing node and zone's present pages via adjust_present_page_count(). These locks are also taken during the initialization of the system at boot time, where it protects parallel struct page initialization, but they should not really be needed in memory-hotplug where all operations are a) synchronized on device level and b) serialized by the mem_hotplug_lock lock. Signed-off-by: Oscar Salvador --- During the review of [1], it was brought up that we might need to revisit the locking scheme in memory-hotplug code wrt. node and zone locks. Given that memory-hotplug is serialized and synchronized by memory-hotplug lock and the device, I do not think we need to hold zone/node's resize lock anymore. After the system has been brought up, memory-hotplug is the only code allow to touch {spanned,present}_pages, so it cannot really go off when serialized by its own lock. Or am I missing something? The only think I am not really sure is: if the from remove_pfn_range_from_zone, shrink_zone_span, update_pgdat_span and move_pfn_range_to_zone can really go (because those functions are already serialized by the memory-hotplug lock), what about mhp_(de)init_memmap_on_memory that calls those functions? Those are not protected by the lock. I have to confess that when it comes to locking in this code, I always have to scratch my head. [1] https://patchwork.kernel.org/project/linux-mm/patch/20210416112411.9826-4-osalvador@suse.de/ mm/memory_hotplug.c | 10 ---------- 1 file changed, 10 deletions(-) diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index 075b34803fec..6edd7e267cad 100644 --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -329,7 +329,6 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn, unsigned long pfn; int nid = zone_to_nid(zone); - zone_span_writelock(zone); if (zone->zone_start_pfn == start_pfn) { /* * If the section is smallest section in the zone, it need @@ -362,7 +361,6 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn, zone->spanned_pages = 0; } } - zone_span_writeunlock(zone); } static void update_pgdat_span(struct pglist_data *pgdat) @@ -424,10 +422,8 @@ void __ref remove_pfn_range_from_zone(struct zone *zone, clear_zone_contiguous(zone); - pgdat_resize_lock(zone->zone_pgdat, &flags); shrink_zone_span(zone, start_pfn, start_pfn + nr_pages); update_pgdat_span(pgdat); - pgdat_resize_unlock(zone->zone_pgdat, &flags); set_zone_contiguous(zone); } @@ -639,14 +635,10 @@ void __ref move_pfn_range_to_zone(struct zone *zone, unsigned long start_pfn, clear_zone_contiguous(zone); /* TODO Huh pgdat is irqsave while zone is not. It used to be like that before */ - pgdat_resize_lock(pgdat, &flags); - zone_span_writelock(zone); if (zone_is_empty(zone)) init_currently_empty_zone(zone, start_pfn, nr_pages); resize_zone_range(zone, start_pfn, nr_pages); - zone_span_writeunlock(zone); resize_pgdat_range(pgdat, start_pfn, nr_pages); - pgdat_resize_unlock(pgdat, &flags); /* * Subsection population requires care in pfn_to_online_page(). @@ -739,9 +731,7 @@ void adjust_present_page_count(struct zone *zone, long nr_pages) unsigned long flags; zone->present_pages += nr_pages; - pgdat_resize_lock(zone->zone_pgdat, &flags); zone->zone_pgdat->node_present_pages += nr_pages; - pgdat_resize_unlock(zone->zone_pgdat, &flags); } int mhp_init_memmap_on_memory(unsigned long pfn, unsigned long nr_pages, -- 2.16.3