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=-8.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 9A650C432C0 for ; Mon, 18 Nov 2019 07:08:35 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 4F54720722 for ; Mon, 18 Nov 2019 07:08:35 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="HWYQdaeo" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4F54720722 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id DA87E6B0003; Mon, 18 Nov 2019 02:08:34 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id D59116B0006; Mon, 18 Nov 2019 02:08:34 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C1FF66B0007; Mon, 18 Nov 2019 02:08:34 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0067.hostedemail.com [216.40.44.67]) by kanga.kvack.org (Postfix) with ESMTP id AB3E46B0003 for ; Mon, 18 Nov 2019 02:08:34 -0500 (EST) Received: from smtpin11.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with SMTP id 206B54DA7 for ; Mon, 18 Nov 2019 07:08:34 +0000 (UTC) X-FDA: 76168520148.11.spade34_8498aaa9a1510 X-HE-Tag: spade34_8498aaa9a1510 X-Filterd-Recvd-Size: 6905 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) by imf31.hostedemail.com (Postfix) with ESMTP for ; Mon, 18 Nov 2019 07:08:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Transfer-Encoding :Content-Type:MIME-Version:References:Message-ID:Subject:Cc:To:From:Date: Sender:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help: List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=8ExZk9kczKbYZaf+JhYjsw3ZlJG/piiUaGK9LX777sQ=; b=HWYQdaeoViTJh8ki1f8oz62GPc S/9Pz7w7AlVu5+aaOjLpiy0pqQiH1U9UzwZUlaqga/snXQcMZ6w+JzwIKPiGvVQZNR+abF4Ymu368 koJGbrV5zpC27FQXI56DpaATg1VIR4EEutNGTtJWQzSKs25LwLh5M/8DHct0IXWa5oJdCrTECNaQr dzmWJQ21ALWiDg6IIPx7Qmk82vaS6wZAsOtdNxFiUVCfB8xSAAYKqIJTLy74ScZXnpZKidUdXu4zk 0dEUeV1Z+nGlNIcnBuJ65GkTrCX5Bq1mbfARwB+2tIz0plZ4rzGpTJ/E7gUJr0c1ogfBzo+Qxe87Z D0dyFaiA==; Received: from hch by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1iWb98-0002G9-83; Mon, 18 Nov 2019 07:08:26 +0000 Date: Sun, 17 Nov 2019 23:08:26 -0800 From: Christoph Hellwig To: John Hubbard Cc: Andrew Morton , Christoph Hellwig , Jan Kara , Jason Gunthorpe , Jens Axboe , =?iso-8859-1?B?Suly9G1l?= Glisse , linux-nvdimm@lists.01.org, linux-mm@kvack.org, LKML , Christoph Hellwig Subject: Re: [PATCH 2/2] mm: devmap: refactor 1-based refcounting for ZONE_DEVICE pages Message-ID: <20191118070826.GB3099@infradead.org> References: <20191115001134.2489505-1-jhubbard@nvidia.com> <20191115001134.2489505-3-jhubbard@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20191115001134.2489505-3-jhubbard@nvidia.com> User-Agent: Mutt/1.12.1 (2019-06-15) X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html 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 Thu, Nov 14, 2019 at 04:11:34PM -0800, John Hubbard wrote: > An upcoming patch changes and complicates the refcounting and > especially the "put page" aspects of it. In order to keep > everything clean, refactor the devmap page release routines: >=20 > * Rename put_devmap_managed_page() to page_is_devmap_managed(), > and limit the functionality to "read only": return a bool, > with no side effects. >=20 > * Add a new routine, put_devmap_managed_page(), to handle checking > what kind of page it is, and what kind of refcount handling it > requires. >=20 > * Rename __put_devmap_managed_page() to free_devmap_managed_page(), > and limit the functionality to unconditionally freeing a devmap > page. >=20 > This is originally based on a separate patch by Ira Weiny, which > applied to an early version of the put_user_page() experiments. > Since then, J=E9r=F4me Glisse suggested the refactoring described above= . I can't say I'm a big fan of this as it adds a lot more inlined code to put_page, which has a lot of callsites. Can't we instead try to figure out a way to move away from the off by one refcounting? >=20 > Cc: Jan Kara > Cc: J=E9r=F4me Glisse > Cc: Christoph Hellwig > Cc: Dan Williams > Suggested-by: J=E9r=F4me Glisse > Signed-off-by: Ira Weiny > Signed-off-by: John Hubbard > --- > include/linux/mm.h | 27 ++++++++++++++++++++++++--- > mm/memremap.c | 16 ++-------------- > 2 files changed, 26 insertions(+), 17 deletions(-) >=20 > diff --git a/include/linux/mm.h b/include/linux/mm.h > index a2adf95b3f9c..96228376139c 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -967,9 +967,10 @@ static inline bool is_zone_device_page(const struc= t page *page) > #endif > =20 > #ifdef CONFIG_DEV_PAGEMAP_OPS > -void __put_devmap_managed_page(struct page *page); > +void free_devmap_managed_page(struct page *page); > DECLARE_STATIC_KEY_FALSE(devmap_managed_key); > -static inline bool put_devmap_managed_page(struct page *page) > + > +static inline bool page_is_devmap_managed(struct page *page) > { > if (!static_branch_unlikely(&devmap_managed_key)) > return false; > @@ -978,7 +979,6 @@ static inline bool put_devmap_managed_page(struct p= age *page) > switch (page->pgmap->type) { > case MEMORY_DEVICE_PRIVATE: > case MEMORY_DEVICE_FS_DAX: > - __put_devmap_managed_page(page); > return true; > default: > break; > @@ -986,6 +986,27 @@ static inline bool put_devmap_managed_page(struct = page *page) > return false; > } > =20 > +static inline bool put_devmap_managed_page(struct page *page) > +{ > + bool is_devmap =3D page_is_devmap_managed(page); > + > + if (is_devmap) { > + int count =3D page_ref_dec_return(page); > + > + /* > + * devmap page refcounts are 1-based, rather than 0-based: if > + * refcount is 1, then the page is free and the refcount is > + * stable because nobody holds a reference on the page. > + */ > + if (count =3D=3D 1) > + free_devmap_managed_page(page); > + else if (!count) > + __put_page(page); > + } > + > + return is_devmap; > +} > + > #else /* CONFIG_DEV_PAGEMAP_OPS */ > static inline bool put_devmap_managed_page(struct page *page) > { > diff --git a/mm/memremap.c b/mm/memremap.c > index e899fa876a62..2ba773859031 100644 > --- a/mm/memremap.c > +++ b/mm/memremap.c > @@ -411,20 +411,8 @@ struct dev_pagemap *get_dev_pagemap(unsigned long = pfn, > EXPORT_SYMBOL_GPL(get_dev_pagemap); > =20 > #ifdef CONFIG_DEV_PAGEMAP_OPS > -void __put_devmap_managed_page(struct page *page) > +void free_devmap_managed_page(struct page *page) > { > - int count =3D page_ref_dec_return(page); > - > - /* still busy */ > - if (count > 1) > - return; > - > - /* only triggered by the dev_pagemap shutdown path */ > - if (count =3D=3D 0) { > - __put_page(page); > - return; > - } > - > /* notify page idle for dax */ > if (!is_device_private_page(page)) { > wake_up_var(&page->_refcount); > @@ -461,5 +449,5 @@ void __put_devmap_managed_page(struct page *page) > page->mapping =3D NULL; > page->pgmap->ops->page_free(page); > } > -EXPORT_SYMBOL(__put_devmap_managed_page); > +EXPORT_SYMBOL(free_devmap_managed_page); > #endif /* CONFIG_DEV_PAGEMAP_OPS */ > --=20 > 2.24.0 > _______________________________________________ > Linux-nvdimm mailing list -- linux-nvdimm@lists.01.org > To unsubscribe send an email to linux-nvdimm-leave@lists.01.org ---end quoted text---