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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY, 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 562A5CA9EBC for ; Fri, 25 Oct 2019 15:58:45 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id BCEAD20663 for ; Fri, 25 Oct 2019 15:58:44 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BCEAD20663 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 6D9026B0006; Fri, 25 Oct 2019 11:58:44 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 689A66B0007; Fri, 25 Oct 2019 11:58:44 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 5C5FD6B0008; Fri, 25 Oct 2019 11:58:44 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0218.hostedemail.com [216.40.44.218]) by kanga.kvack.org (Postfix) with ESMTP id 39E686B0006 for ; Fri, 25 Oct 2019 11:58:44 -0400 (EDT) Received: from smtpin16.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with SMTP id D24F54995E4 for ; Fri, 25 Oct 2019 15:58:43 +0000 (UTC) X-FDA: 76082764926.16.truck84_1193fe8a42b0a X-HE-Tag: truck84_1193fe8a42b0a X-Filterd-Recvd-Size: 4008 Received: from out30-44.freemail.mail.aliyun.com (out30-44.freemail.mail.aliyun.com [115.124.30.44]) by imf15.hostedemail.com (Postfix) with ESMTP for ; Fri, 25 Oct 2019 15:58:40 +0000 (UTC) X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R991e4;CH=green;DM=||false|;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01f04446;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=7;SR=0;TI=SMTPD_---0TgBMTJi_1572019105; Received: from US-143344MP.local(mailfrom:yang.shi@linux.alibaba.com fp:SMTPD_---0TgBMTJi_1572019105) by smtp.aliyun-inc.com(127.0.0.1); Fri, 25 Oct 2019 23:58:28 +0800 Subject: Re: [PATCH] mm: thp: clear PageDoubleMap flag when the last PMD map gone To: "Kirill A. Shutemov" Cc: hughd@google.com, kirill.shutemov@linux.intel.com, aarcange@redhat.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1571938066-29031-1-git-send-email-yang.shi@linux.alibaba.com> <20191025153618.ajcecye3bjm5abax@box> From: Yang Shi Message-ID: <74becfc0-3c34-bdd2-02cd-25b763c92f3b@linux.alibaba.com> Date: Fri, 25 Oct 2019 08:58:22 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <20191025153618.ajcecye3bjm5abax@box> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: quoted-printable 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 10/25/19 8:36 AM, Kirill A. Shutemov wrote: > On Fri, Oct 25, 2019 at 01:27:46AM +0800, Yang Shi wrote: >> File THP sets PageDoubleMap flag when the first it gets PTE mapped, bu= t >> the flag is never cleared until the THP is freed. This result in >> unbalanced state although it is not a big deal. >> >> Clear the flag when the last compound_mapcount is gone. It should be >> cleared when all the PTE maps are gone (become PMD mapped only) as wel= l, >> but this needs check all subpage's _mapcount every time any subpage's >> rmap is removed, the overhead may be not worth. The anonymous THP als= o >> just clears PageDoubleMap flag when the last PMD map is gone. > NAK, sorry. > > The key difference with anon THP that file THP can be mapped again with > PMD after all PMD (or all) mappings are gone. > > Your patch breaks the case when you map the page with PMD again while t= he > page is still mapped with PTEs. Who would set PageDoubleMap() in this > case? Aha, yes, you are right. I missed that point. However, I'm wondering we=20 might move this up a little bit like this: diff --git a/mm/rmap.c b/mm/rmap.c index d17cbf3..ac046fd 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1230,15 +1230,17 @@ static void page_remove_file_rmap(struct page=20 *page, bool compound) =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (at= omic_add_negative(-1, &page[i]._mapcount)) =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 nr++; =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0 } + +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0 /* No PTE map anymore */ +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0 if (nr =3D=3D HPAGE_PMD_NR) +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 ClearPageDou= bleMap(compound_head(page)); + =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0 if (!atomic_add_negative(-1, compound_mapcount_ptr(pag= e))) =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 goto o= ut; =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0 if (PageSwapBacked(page)) =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 __dec_= node_page_state(page, NR_SHMEM_PMDMAPPED); =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0 else =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 __dec_= node_page_state(page, NR_FILE_PMDMAPPED); - -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0 /* The last PMD map is gone */ -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0 ClearPageDoubleMap(compound_head(page)); =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 } else { =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0 if (!atomic_add_negative(-1, &page->_mapcount)) =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 goto o= ut; This should guarantee no PTE map anymore, it should be safe to clear the=20 flag. >