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 4C4A7EB64DA for ; Tue, 18 Jul 2023 08:58:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231927AbjGRI6f (ORCPT ); Tue, 18 Jul 2023 04:58:35 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42860 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231912AbjGRI6c (ORCPT ); Tue, 18 Jul 2023 04:58:32 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 428B4172C for ; Tue, 18 Jul 2023 01:58:09 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 689522F4; Tue, 18 Jul 2023 01:58:52 -0700 (PDT) Received: from [10.1.34.52] (C02Z41KALVDN.cambridge.arm.com [10.1.34.52]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 88D0C3F67D; Tue, 18 Jul 2023 01:58:07 -0700 (PDT) Message-ID: <7319a1aa-7c72-82e9-f26d-eeccb6fdf35b@arm.com> Date: Tue, 18 Jul 2023 09:58:04 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: [PATCH v1 1/3] mm: Allow deferred splitting of arbitrary large anon folios To: David Hildenbrand , Andrew Morton , Matthew Wilcox , Yin Fengwei , Yu Zhao , Yang Shi , "Huang, Ying" , Zi Yan Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20230717143110.260162-1-ryan.roberts@arm.com> <20230717143110.260162-2-ryan.roberts@arm.com> <90b406af-9db4-b668-a7a0-e574e104c84c@redhat.com> <028c5f5b-b67c-9ccc-bc06-468f47362999@arm.com> <0250a2d7-c79b-0e0f-8161-bf475daf1c82@redhat.com> From: Ryan Roberts In-Reply-To: <0250a2d7-c79b-0e0f-8161-bf475daf1c82@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 17/07/2023 17:48, David Hildenbrand wrote: > On 17.07.23 18:01, Ryan Roberts wrote: >> On 17/07/2023 16:42, David Hildenbrand wrote: >>> On 17.07.23 16:31, Ryan Roberts wrote: >>>> In preparation for the introduction of large folios for anonymous >>>> memory, we would like to be able to split them when they have unmapped >>>> subpages, in order to free those unused pages under memory pressure. So >>>> remove the artificial requirement that the large folio needed to be at >>>> least PMD-sized. >>>> >>>> Signed-off-by: Ryan Roberts >>>> Reviewed-by: Yu Zhao >>>> Reviewed-by: Yin Fengwei >>>> --- >>>>    mm/rmap.c | 2 +- >>>>    1 file changed, 1 insertion(+), 1 deletion(-) >>>> >>>> diff --git a/mm/rmap.c b/mm/rmap.c >>>> index 0c0d8857dfce..2baf57d65c23 100644 >>>> --- a/mm/rmap.c >>>> +++ b/mm/rmap.c >>>> @@ -1430,7 +1430,7 @@ void page_remove_rmap(struct page *page, struct >>>> vm_area_struct *vma, >>>>             * page of the folio is unmapped and at least one page >>>>             * is still mapped. >>>>             */ >>>> -        if (folio_test_pmd_mappable(folio) && folio_test_anon(folio)) >>>> +        if (folio_test_large(folio) && folio_test_anon(folio)) >>>>                if (!compound || nr < nr_pmdmapped) >>>>                    deferred_split_folio(folio); >>> >>> !compound will always be true I guess, so nr_pmdmapped == 0 (which will always >>> be the case) will be ignored. >> >> I don't follow why !compound will always be true. This function is >> page_remove_rmap() (not folio_remove_rmap_range() which I add in a later patch). >> page_remove_rmap() can work on pmd-mapped pages where compound=true is passed in. > > I was talking about the folio_test_pmd_mappable() -> folio_test_large() change. > For folio_test_large() && !folio_test_pmd_mappable() I expect that we'll never > pass in "compound=true". > Sorry David, I've been staring at the code and your comment, and I still don't understand your point. I assumed you were trying to say that compound is always false and therefore "if (!compound || nr < nr_pmdmapped)" can be removed? But its not the case that compound is always false; it will be true when called to remove a pmd-mapped compound page. What change are you suggesting, exactly?