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=-5.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,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 0D276CA9EA0 for ; Fri, 25 Oct 2019 16:32:39 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id B949320663 for ; Fri, 25 Oct 2019 16:32:37 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=shutemov-name.20150623.gappssmtp.com header.i=@shutemov-name.20150623.gappssmtp.com header.b="K4yRjbQE" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B949320663 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=shutemov.name Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 784666B0007; Fri, 25 Oct 2019 12:32:37 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 735946B0008; Fri, 25 Oct 2019 12:32:37 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6247B6B000A; Fri, 25 Oct 2019 12:32:37 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0018.hostedemail.com [216.40.44.18]) by kanga.kvack.org (Postfix) with ESMTP id 415126B0007 for ; Fri, 25 Oct 2019 12:32:37 -0400 (EDT) Received: from smtpin17.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with SMTP id DB6B14DA7 for ; Fri, 25 Oct 2019 16:32:36 +0000 (UTC) X-FDA: 76082850312.17.burn45_16bf015cce821 X-HE-Tag: burn45_16bf015cce821 X-Filterd-Recvd-Size: 5940 Received: from mail-lj1-f193.google.com (mail-lj1-f193.google.com [209.85.208.193]) by imf37.hostedemail.com (Postfix) with ESMTP for ; Fri, 25 Oct 2019 16:32:36 +0000 (UTC) Received: by mail-lj1-f193.google.com with SMTP id q64so3355778ljb.12 for ; Fri, 25 Oct 2019 09:32:36 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=shutemov-name.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:content-transfer-encoding:in-reply-to :user-agent; bh=aUvEx9HZvsTIgPUyMH5XlBDc9GALQrMIKIvZ3DuSPEE=; b=K4yRjbQEIhHrz72615nejLKsPfEKEXSttAY8z13wpdqpymVE4fAgpjXH577G8erpJp pnWCcDd56eyjzLXuNN8ftFCqXRQDoJuE23SGVLLpYnEnt7DOTa9P0mK9yp3SvwJF5Gh/ duKOZsYXF0jtGsL/T1jLYXH4gVR00Sa1cRbNfy+/k8gKPHMRj2fNk3DP88GFHDk10I+V S3K+QL7e3B5uL4iSV4qJx/HbGlImKWxScqyMEBAQxYIKN7Xm5D13SAwrKE6Q7lR+RDjE kD/4LpGdtYUh3Xm2saT3p6A/MB+mcARzhaQtfTt5IHXxaT5sBNfLUHJDOgGJZFZZJ+RL dRyw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:content-transfer-encoding :in-reply-to:user-agent; bh=aUvEx9HZvsTIgPUyMH5XlBDc9GALQrMIKIvZ3DuSPEE=; b=OvXKEjqY94NASYo1BVhFFUgvre83yLvwq444LFA9huweSqR1j1T4fHIuRDQ/pq/zht +RAMj1dm4zoY76wcBGPSF8k/NIXzEyhPWBfbcFr08rD5bcxDG0Kq5azFoWg8aeOAOOC4 uDzNvUISJxdpMERK1dteod+ttxi79Eq2FA7lv06UBN2Fbq6OxAoAhc+RH37cFMrgFQ0j TrwSazYJ+A/pG308ipRDbaqEWt1Jl1HSIBvQxzLP5C+YyQjY3FkfS0Y0DkoLIhA7lYKa 9EQWws5uxyMSoMSx7/LCHzbmViIoy2y1GZUSsxtWBRURImKgrOPKzPKMt3ocOGiZ5rA6 CCDw== X-Gm-Message-State: APjAAAUrDUP/k1Pf7yzfFFN8ty7260YUoaLRlLJUTXFSNxzVzft1ZcM1 EXf526/qpUmjTs8cJvhALlxjSA== X-Google-Smtp-Source: APXvYqx5yh5D5PJ2m8iKys+639ad4qNRhItdC2ximujxlbmn+F6Uufeub3RzZ8JPxk2mQn+TrBH/IQ== X-Received: by 2002:a2e:8654:: with SMTP id i20mr3121136ljj.238.1572021154458; Fri, 25 Oct 2019 09:32:34 -0700 (PDT) Received: from box.localdomain ([86.57.175.117]) by smtp.gmail.com with ESMTPSA id y28sm984004lfg.31.2019.10.25.09.32.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 25 Oct 2019 09:32:33 -0700 (PDT) Received: by box.localdomain (Postfix, from userid 1000) id 7864010267F; Fri, 25 Oct 2019 19:32:33 +0300 (+03) Date: Fri, 25 Oct 2019 19:32:33 +0300 From: "Kirill A. Shutemov" To: Yang Shi 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 Subject: Re: [PATCH] mm: thp: clear PageDoubleMap flag when the last PMD map gone Message-ID: <20191025163233.myl7kcgz25qsbnwm@box> References: <1571938066-29031-1-git-send-email-yang.shi@linux.alibaba.com> <20191025153618.ajcecye3bjm5abax@box> <74becfc0-3c34-bdd2-02cd-25b763c92f3b@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <74becfc0-3c34-bdd2-02cd-25b763c92f3b@linux.alibaba.com> User-Agent: NeoMutt/20180716 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 Fri, Oct 25, 2019 at 08:58:22AM -0700, Yang Shi wrote: >=20 >=20 > 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,= but > > > the flag is never cleared until the THP is freed. This result in > > > unbalanced state although it is not a big deal. > > >=20 > > > 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 = well, > > > 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 = also > > > just clears PageDoubleMap flag when the last PMD map is gone. > > NAK, sorry. > >=20 > > The key difference with anon THP that file THP can be mapped again wi= th > > PMD after all PMD (or all) mappings are gone. > >=20 > > Your patch breaks the case when you map the page with PMD again while= the > > page is still mapped with PTEs. Who would set PageDoubleMap() in this > > case? >=20 > Aha, yes, you are right. I missed that point. However, I'm wondering we > might move this up a little bit like this: >=20 > 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 *= page, > bool compound) > =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 i= f (atomic_add_negative(-1, &page[i]._mapcount)) > =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0=A0=A0=A0=A0=A0=A0 nr++; > =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 } > + > +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 /* No PTE map anymore */ > +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 if (nr =3D=3D HPAGE_PMD_NR) > +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 Cle= arPageDoubleMap(compound_head(page)); > + > =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 if (!atomic_add_negative(= -1, compound_mapcount_ptr(page))) > =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 g= oto out; > =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 if (PageSwapBacked(page)) > =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 _= _dec_node_page_state(page, NR_SHMEM_PMDMAPPED); > =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 else > =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 _= _dec_node_page_state(page, NR_FILE_PMDMAPPED); > - > -=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 /* The last PMD map is gone= */ > -=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 ClearPageDoubleMap(compound= _head(page)); > =A0=A0=A0=A0=A0=A0=A0 } else { > =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 if (!atomic_add_negative(= -1, &page->_mapcount)) > =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 g= oto out; >=20 >=20 > This should guarantee no PTE map anymore, it should be safe to clear th= e > flag. At first glance looks safe, but let me think more about it. I didn't expect it be that easy :P --=20 Kirill A. Shutemov