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=-17.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,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 B306FC433DB for ; Tue, 12 Jan 2021 11:34:14 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 3392C22B37 for ; Tue, 12 Jan 2021 11:34:14 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3392C22B37 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id AC6C86B00C6; Tue, 12 Jan 2021 06:34:13 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id A755D6B00C8; Tue, 12 Jan 2021 06:34:13 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 93EF28D0090; Tue, 12 Jan 2021 06:34:13 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0244.hostedemail.com [216.40.44.244]) by kanga.kvack.org (Postfix) with ESMTP id 7D4D76B00C6 for ; Tue, 12 Jan 2021 06:34:13 -0500 (EST) Received: from smtpin26.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 416341EE6 for ; Tue, 12 Jan 2021 11:34:13 +0000 (UTC) X-FDA: 77696914386.26.hot44_1f0c85827515 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin26.hostedemail.com (Postfix) with ESMTP id 165331804B640 for ; Tue, 12 Jan 2021 11:34:13 +0000 (UTC) X-HE-Tag: hot44_1f0c85827515 X-Filterd-Recvd-Size: 5503 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [216.205.24.124]) by imf09.hostedemail.com (Postfix) with ESMTP for ; Tue, 12 Jan 2021 11:34:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1610451252; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=HFXsqS//Qa1h2ehQGzspg6CEoG46NmAqT6A5EbYgQ7k=; b=Wr6RPDnGLGDUanD/THq3oNte3/hLCTmn+X0i2VjN6XTC/5Xr+JqsAIcVGZ/imh4+qoOemz 7t+g4dQPVTjglqTFLbGCP1KWE+hfqrjBl/O9TU2LhfpIHnUXMg58kd/+Kme0eRLiYr2Giu E2fcwf5KBq81GFHdYFuC9KeEjidsgUI= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-235-GkizPVrCNcWYPTmkRdWF4w-1; Tue, 12 Jan 2021 06:34:08 -0500 X-MC-Unique: GkizPVrCNcWYPTmkRdWF4w-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 43DF28145F0; Tue, 12 Jan 2021 11:34:06 +0000 (UTC) Received: from [10.36.115.140] (ovpn-115-140.ams2.redhat.com [10.36.115.140]) by smtp.corp.redhat.com (Postfix) with ESMTP id F3C6C60CBB; Tue, 12 Jan 2021 11:34:02 +0000 (UTC) Subject: Re: [PATCH v3 1/6] mm: migrate: do not migrate HugeTLB page whose refcount is one To: Michal Hocko Cc: Muchun Song , mike.kravetz@oracle.com, akpm@linux-foundation.org, n-horiguchi@ah.jp.nec.com, ak@linux.intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Yang Shi References: <20210110124017.86750-1-songmuchun@bytedance.com> <20210110124017.86750-2-songmuchun@bytedance.com> <1b39d654-0b8c-de3a-55d1-6ab8c2b2e0ba@redhat.com> <20210112112709.GO22493@dhcp22.suse.cz> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: Date: Tue, 12 Jan 2021 12:34:01 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.0 MIME-Version: 1.0 In-Reply-To: <20210112112709.GO22493@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 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: On 12.01.21 12:27, Michal Hocko wrote: > On Tue 12-01-21 12:11:21, David Hildenbrand wrote: >> On 12.01.21 12:00, David Hildenbrand wrote: >>> On 10.01.21 13:40, Muchun Song wrote: >>>> If the refcount is one when it is migrated, it means that the page >>>> was freed from under us. So we are done and do not need to migrate. >>>> >>>> This optimization is consistent with the regular pages, just like >>>> unmap_and_move() does. >>>> >>>> Signed-off-by: Muchun Song >>>> Reviewed-by: Mike Kravetz >>>> Acked-by: Yang Shi >>>> --- >>>> mm/migrate.c | 6 ++++++ >>>> 1 file changed, 6 insertions(+) >>>> >>>> diff --git a/mm/migrate.c b/mm/migrate.c >>>> index 4385f2fb5d18..a6631c4eb6a6 100644 >>>> --- a/mm/migrate.c >>>> +++ b/mm/migrate.c >>>> @@ -1279,6 +1279,12 @@ static int unmap_and_move_huge_page(new_page_t get_new_page, >>>> return -ENOSYS; >>>> } >>>> >>>> + if (page_count(hpage) == 1) { >>>> + /* page was freed from under us. So we are done. */ >>>> + putback_active_hugepage(hpage); >>>> + return MIGRATEPAGE_SUCCESS; >>>> + } >>>> + >>>> new_hpage = get_new_page(hpage, private); >>>> if (!new_hpage) >>>> return -ENOMEM; >>>> >>> >>> Question: What if called via alloc_contig_range() where we even want to >>> "migrate" free pages, meaning, relocate it? >>> >> >> To be more precise: >> >> a) We don't have dissolve_free_huge_pages() calls on the >> alloc_contig_range() path. So we *need* migration IIUC. >> >> b) dissolve_free_huge_pages() will fail if going below the reservation. >> In that case we really want to migrate free pages. This even applies to >> memory offlining. >> >> Either I am missing something important or this patch is more dangerous >> than it looks like. > > This is an interesting point. But do we try to migrate hugetlb pages in > alloc_contig_range? isolate_migratepages_block !PageLRU need to be I didn't test it so far (especially in the context of virtio-mem or CMA), but have a TODO item on my long list of things to look at in the future. > marked as PageMovable AFAICS. This would be quite easy to implement but > a more fundamental question is whether we really want to mess with > existing pools for alloc_contig_range. Can these pages fall onto ZONE_MOVABLE or even MIGRATE_CMA? If yes, we really want to. And I think both is the case for "ordinary" huge pages allocated via the buddy. > > Anyway you are quite right that this change has more side effects than > it is easy to see while it doesn't really bring any major advantage > other than the consistency. Free hugetlbfs pages are special. E.g., they cannot simply be skipped when offlining. So I don't think consistency actually really applies. -- Thanks, David / dhildenb