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=-8.3 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 F1E5FC43215 for ; Wed, 13 Nov 2019 23:03:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C9B38206E3 for ; Wed, 13 Nov 2019 23:03:52 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Tn/huwhf" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726303AbfKMXDv (ORCPT ); Wed, 13 Nov 2019 18:03:51 -0500 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:55996 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726251AbfKMXDu (ORCPT ); Wed, 13 Nov 2019 18:03:50 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1573686229; 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=XjW0CpMRM7lIuk5UP56xIe9TjleU12DYiFXbT2LVzkE=; b=Tn/huwhfSqiBPFiOvUIYoWMNx3+3r86V3ddRNJCNVe/5xAAgukAmsmM7wqfxSGncthCTio oAG7YJmAft/E2rTfcVqaSuZ1eFa+16UHqim9u3uUzQA8Mv9As+Y6d/mWTteGl6ADRPWVdy ZBMIOKtvFO6o9u2dYjmJjHI+TQ/aaPc= 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-368-rGYPkL_YNcCM_ji45nIZag-1; Wed, 13 Nov 2019 18:03:45 -0500 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 411F11852E21; Wed, 13 Nov 2019 23:03:41 +0000 (UTC) Received: from redhat.com (ovpn-121-71.rdu2.redhat.com [10.10.121.71]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B8980691AE; Wed, 13 Nov 2019 23:03:33 +0000 (UTC) Date: Wed, 13 Nov 2019 18:03:31 -0500 From: Jerome Glisse To: Dan Williams Cc: John Hubbard , Andrew Morton , Al Viro , Alex Williamson , Benjamin Herrenschmidt , =?iso-8859-1?Q?Bj=F6rn_T=F6pel?= , Christoph Hellwig , Daniel Vetter , Dave Chinner , David Airlie , "David S . Miller" , Ira Weiny , Jan Kara , Jason Gunthorpe , Jens Axboe , Jonathan Corbet , Magnus Karlsson , Mauro Carvalho Chehab , Michael Ellerman , Michal Hocko , Mike Kravetz , Paul Mackerras , Shuah Khan , Vlastimil Babka , bpf@vger.kernel.org, Maling list - DRI developers , KVM list , linux-block@vger.kernel.org, Linux Doc Mailing List , linux-fsdevel , linux-kselftest@vger.kernel.org, "Linux-media@vger.kernel.org" , linux-rdma , linuxppc-dev , Netdev , Linux MM , LKML Subject: Re: [PATCH v4 04/23] mm: devmap: refactor 1-based refcounting for ZONE_DEVICE pages Message-ID: <20191113230331.GB6171@redhat.com> References: <20191113042710.3997854-1-jhubbard@nvidia.com> <20191113042710.3997854-5-jhubbard@nvidia.com> MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-MC-Unique: rGYPkL_YNcCM_ji45nIZag-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: quoted-printable Content-Disposition: inline Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Wed, Nov 13, 2019 at 02:00:06PM -0800, Dan Williams wrote: > On Wed, Nov 13, 2019 at 11:23 AM Dan Williams = wrote: > > > > On Tue, Nov 12, 2019 at 8:27 PM John Hubbard wrot= e: > > > > > > 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: > > > > > > * Rename put_devmap_managed_page() to page_is_devmap_managed(), > > > and limit the functionality to "read only": return a bool, > > > with no side effects. > > > > > > * 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. > > > > > > * Rename __put_devmap_managed_page() to free_devmap_managed_page(), > > > and limit the functionality to unconditionally freeing a devmap > > > page. > > > > > > 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 abo= ve. > > > > > > Suggested-by: J=E9r=F4me Glisse > > > Signed-off-by: Ira Weiny > > > Signed-off-by: John Hubbard > > > --- > > > include/linux/mm.h | 27 ++++++++++++++++--- > > > mm/memremap.c | 67 ++++++++++++++++++++------------------------= -- > > > 2 files changed, 53 insertions(+), 41 deletions(-) > > > > > > 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 str= uct page *page) > > > #endif > > > > > > #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= page *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(struc= t page *page) > > > return false; > > > } > > > > > > +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-b= ased: if > > > + * refcount is 1, then the page is free and the refco= unt is > > > + * stable because nobody holds a reference on the pag= e. > > > + */ > > > + 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 03ccbdfeb697..bc7e2a27d025 100644 > > > --- a/mm/memremap.c > > > +++ b/mm/memremap.c > > > @@ -410,48 +410,39 @@ struct dev_pagemap *get_dev_pagemap(unsigned lo= ng pfn, > > > EXPORT_SYMBOL_GPL(get_dev_pagemap); > > > > > > #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); > > > + /* Clear Active bit in case of parallel mark_page_accessed */ > > > + __ClearPageActive(page); > > > + __ClearPageWaiters(page); > > > + > > > + mem_cgroup_uncharge(page); > > > > Ugh, when did all this HMM specific manipulation sneak into the > > generic ZONE_DEVICE path? It used to be gated by pgmap type with its > > own put_zone_device_private_page(). For example it's certainly > > unnecessary and might be broken (would need to check) to call > > mem_cgroup_uncharge() on a DAX page. ZONE_DEVICE users are not a > > monolith and the HMM use case leaks pages into code paths that DAX > > explicitly avoids. >=20 > It's been this way for a while and I did not react previously, > apologies for that. I think __ClearPageActive, __ClearPageWaiters, and > mem_cgroup_uncharge, belong behind a device-private conditional. The > history here is: >=20 > Move some, but not all HMM specifics to hmm_devmem_free(): > 2fa147bdbf67 mm, dev_pagemap: Do not clear ->mapping on final put >=20 > Remove the clearing of mapping since no upstream consumers needed it: > b7a523109fb5 mm: don't clear ->mapping in hmm_devmem_free >=20 > Add it back in once an upstream consumer arrived: > 7ab0ad0e74f8 mm/hmm: fix ZONE_DEVICE anon page mapping reuse >=20 > We're now almost entirely free of ->page_free callbacks except for > that weird nouveau case, can that FIXME in nouveau_dmem_page_free() > also result in killing the ->page_free() callback altogether? In the > meantime I'm proposing a cleanup like this: No we need the callback, cleanup looks good. >=20 > diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c > index ad8e4df1282b..4eae441f86c9 100644 > --- a/drivers/nvdimm/pmem.c > +++ b/drivers/nvdimm/pmem.c > @@ -337,13 +337,7 @@ static void pmem_release_disk(void *__pmem) > put_disk(pmem->disk); > } >=20 > -static void pmem_pagemap_page_free(struct page *page) > -{ > - wake_up_var(&page->_refcount); > -} > - > static const struct dev_pagemap_ops fsdax_pagemap_ops =3D { > - .page_free =3D pmem_pagemap_page_free, > .kill =3D pmem_pagemap_kill, > .cleanup =3D pmem_pagemap_cleanup, > }; > diff --git a/mm/memremap.c b/mm/memremap.c > index 03ccbdfeb697..157edb8f7cf8 100644 > --- a/mm/memremap.c > +++ b/mm/memremap.c > @@ -419,12 +419,6 @@ void __put_devmap_managed_page(struct page *page) > * holds a reference on the page. > */ > if (count =3D=3D 1) { > - /* Clear Active bit in case of parallel mark_page_accesse= d */ > - __ClearPageActive(page); > - __ClearPageWaiters(page); > - > - mem_cgroup_uncharge(page); > - > /* > * When a device_private page is freed, the page->mapping= field > * may still contain a (stale) mapping value. For example= , the > @@ -446,10 +440,17 @@ void __put_devmap_managed_page(struct page *page) > * handled differently or not done at all, so there is no= need > * to clear page->mapping. > */ > - if (is_device_private_page(page)) > - page->mapping =3D NULL; > + if (is_device_private_page(page)) { > + /* Clear Active bit in case of parallel > mark_page_accessed */ > + __ClearPageActive(page); > + __ClearPageWaiters(page); >=20 > - page->pgmap->ops->page_free(page); > + mem_cgroup_uncharge(page); > + > + page->mapping =3D NULL; > + page->pgmap->ops->page_free(page); > + } else > + wake_up_var(&page->_refcount); > } else if (!count) > __put_page(page); > } >=20