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=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 37B29C433E0 for ; Tue, 12 Jan 2021 13:53:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EA42D23104 for ; Tue, 12 Jan 2021 13:53:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729081AbhALNxH (ORCPT ); Tue, 12 Jan 2021 08:53:07 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:30525 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726236AbhALNxH (ORCPT ); Tue, 12 Jan 2021 08:53:07 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1610459500; 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=VqV6xUNCn3zaauF+LhOcuwhDVizk+gj2YN6AZWHRrPo=; b=dBA8uVFMKzgT2VpuOKTnV4EBG/owxfqJMe5FVBlqb94vDzeJ02yol5PaoDCyRoT5cgx4hy JVTbOyP2z9ARHFdqi/YB9ioEdUvbydDJEaI0HvjU/1n3JzDPK9dsz8gLuIalrP5jZQbT+Y n8poSRL2Ytnib0CARlvJc5dJrJg/XrQ= 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-221-C3XE_pOpPASBYhPOkH5WOQ-1; Tue, 12 Jan 2021 08:51:36 -0500 X-MC-Unique: C3XE_pOpPASBYhPOkH5WOQ-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id E1A508144E7; Tue, 12 Jan 2021 13:51:34 +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 EEF455C239; Tue, 12 Jan 2021 13:51:31 +0000 (UTC) Subject: Re: [External] Re: [PATCH v3 1/6] mm: migrate: do not migrate HugeTLB page whose refcount is one To: Muchun Song Cc: Mike Kravetz , Andrew Morton , Naoya Horiguchi , Andi Kleen , mhocko@suse.cz, Linux Memory Management List , LKML , Yang Shi References: <20210110124017.86750-1-songmuchun@bytedance.com> <20210110124017.86750-2-songmuchun@bytedance.com> <1b39d654-0b8c-de3a-55d1-6ab8c2b2e0ba@redhat.com> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: <423ee403-bba7-acf6-8934-9db36d3a719a@redhat.com> Date: Tue, 12 Jan 2021 14:51:31 +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: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12.01.21 14:40, Muchun Song wrote: > On Tue, Jan 12, 2021 at 7:11 PM 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. > > Without this patch, if you want to migrate a HUgeTLB page, > the page is freed to the hugepage pool. With this patch, > the page is also freed to the hugepage pool. > I didn't see any different. I am missing something? I am definitely not an expert on hugetlb pools, that's why I am asking. Isn't it, that with your code, no new page is allocated - so dissolve_free_huge_pages() might just refuse to dissolve due to reservations, bailing out, no? (as discussed, looks like alloc_contig_range() needs to be fixed to handle this correctly) -- Thanks, David / dhildenb