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 63E40CA9ED4 for ; Mon, 4 Nov 2019 17:33:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3E75D20B7C for ; Mon, 4 Nov 2019 17:33:48 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="GQpRsC5b" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729304AbfKDRdp (ORCPT ); Mon, 4 Nov 2019 12:33:45 -0500 Received: from us-smtp-1.mimecast.com ([207.211.31.81]:32576 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1729305AbfKDRdo (ORCPT ); Mon, 4 Nov 2019 12:33:44 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1572888822; 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=yb3yyO2PYYBql1Fagu7xeohR5a32M0AhAOb3BjMNyXY=; b=GQpRsC5biVZrcUCmm8/d04vdDBWTuHXVl8fb8jnmz/BzWrplmXBDOnR98lt+lHYe5O/hHE 9oWG3Fr/fLPXSyC3dqzkScENA9u159VHaMg1ma8eS+XpmYO3EEfQKxKr2ZNHoMSNcYUrNr J/0gg23fD/hQuRHU0rEkm6E4WJ5AkjI= 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-149-BOKr1PBBNByJ6qT6wX4yEA-1; Mon, 04 Nov 2019 12:33:38 -0500 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 847CA8017DD; Mon, 4 Nov 2019 17:33:33 +0000 (UTC) Received: from redhat.com (unknown [10.20.6.178]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 89C995C557; Mon, 4 Nov 2019 17:33:27 +0000 (UTC) Date: Mon, 4 Nov 2019 12:33:25 -0500 From: Jerome Glisse To: John Hubbard Cc: Andrew Morton , Al Viro , Alex Williamson , Benjamin Herrenschmidt , =?iso-8859-1?Q?Bj=F6rn_T=F6pel?= , Christoph Hellwig , Dan Williams , 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, dri-devel@lists.freedesktop.org, kvm@vger.kernel.org, linux-block@vger.kernel.org, linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-media@vger.kernel.org, linux-rdma@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, netdev@vger.kernel.org, linux-mm@kvack.org, LKML Subject: Re: [PATCH v2 05/18] mm/gup: introduce pin_user_pages*() and FOLL_PIN Message-ID: <20191104173325.GD5134@redhat.com> References: <20191103211813.213227-1-jhubbard@nvidia.com> <20191103211813.213227-6-jhubbard@nvidia.com> MIME-Version: 1.0 In-Reply-To: <20191103211813.213227-6-jhubbard@nvidia.com> User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-MC-Unique: BOKr1PBBNByJ6qT6wX4yEA-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: quoted-printable Content-Disposition: inline Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Sun, Nov 03, 2019 at 01:18:00PM -0800, John Hubbard wrote: > Introduce pin_user_pages*() variations of get_user_pages*() calls, > and also pin_longterm_pages*() variations. >=20 > These variants all set FOLL_PIN, which is also introduced, and > thoroughly documented. >=20 > The pin_longterm*() variants also set FOLL_LONGTERM, in addition > to FOLL_PIN: >=20 > pin_user_pages() > pin_user_pages_remote() > pin_user_pages_fast() >=20 > pin_longterm_pages() > pin_longterm_pages_remote() > pin_longterm_pages_fast() >=20 > All pages that are pinned via the above calls, must be unpinned via > put_user_page(). >=20 > The underlying rules are: >=20 > * These are gup-internal flags, so the call sites should not directly > set FOLL_PIN nor FOLL_LONGTERM. That behavior is enforced with > assertions, for the new FOLL_PIN flag. However, for the pre-existing > FOLL_LONGTERM flag, which has some call sites that still directly > set FOLL_LONGTERM, there is no assertion yet. >=20 > * Call sites that want to indicate that they are going to do DirectIO > ("DIO") or something with similar characteristics, should call a > get_user_pages()-like wrapper call that sets FOLL_PIN. These wrappers > will: > * Start with "pin_user_pages" instead of "get_user_pages". That > makes it easy to find and audit the call sites. > * Set FOLL_PIN >=20 > * For pages that are received via FOLL_PIN, those pages must be returned > via put_user_page(). >=20 > Thanks to Jan Kara and Vlastimil Babka for explaining the 4 cases > in this documentation. (I've reworded it and expanded on it slightly.) >=20 > Cc: Jonathan Corbet > Cc: Ira Weiny > Signed-off-by: John Hubbard Few nitpick belows, nonetheless: Reviewed-by: J=E9r=F4me Glisse > --- > Documentation/vm/index.rst | 1 + > Documentation/vm/pin_user_pages.rst | 212 ++++++++++++++++++++++ > include/linux/mm.h | 62 ++++++- > mm/gup.c | 265 +++++++++++++++++++++++++--- > 4 files changed, 514 insertions(+), 26 deletions(-) > create mode 100644 Documentation/vm/pin_user_pages.rst >=20 [...] > diff --git a/Documentation/vm/pin_user_pages.rst b/Documentation/vm/pin_u= ser_pages.rst > new file mode 100644 > index 000000000000..3910f49ca98c > --- /dev/null > +++ b/Documentation/vm/pin_user_pages.rst [...] > + > +FOLL_PIN, FOLL_GET, FOLL_LONGTERM: when to use which flags > +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D > + > +Thanks to Jan Kara, Vlastimil Babka and several other -mm people, for de= scribing > +these categories: > + > +CASE 1: Direct IO (DIO) > +----------------------- > +There are GUP references to pages that are serving > +as DIO buffers. These buffers are needed for a relatively short time (so= they > +are not "long term"). No special synchronization with page_mkclean() or > +munmap() is provided. Therefore, flags to set at the call site are: :: > + > + FOLL_PIN > + > +...but rather than setting FOLL_PIN directly, call sites should use one = of > +the pin_user_pages*() routines that set FOLL_PIN. > + > +CASE 2: RDMA > +------------ > +There are GUP references to pages that are serving as DMA > +buffers. These buffers are needed for a long time ("long term"). No spec= ial > +synchronization with page_mkclean() or munmap() is provided. Therefore, = flags > +to set at the call site are: :: > + > + FOLL_PIN | FOLL_LONGTERM > + > +NOTE: Some pages, such as DAX pages, cannot be pinned with longterm pins= . That's > +because DAX pages do not have a separate page cache, and so "pinning" im= plies > +locking down file system blocks, which is not (yet) supported in that wa= y. > + > +CASE 3: ODP > +----------- > +(Mellanox/Infiniband On Demand Paging: the hardware supports > +replayable page faulting). There are GUP references to pages serving as = DMA > +buffers. For ODP, MMU notifiers are used to synchronize with page_mkclea= n() > +and munmap(). Therefore, normal GUP calls are sufficient, so neither fla= g > +needs to be set. I would not include ODP or anything like it here, they do not use GUP anymore and i believe it is more confusing here. I would how- ever include some text in this documentation explaining that hard- ware that support page fault is superior as it does not incur any of the issues described here. > + > +CASE 4: Pinning for struct page manipulation only > +------------------------------------------------- > +Here, normal GUP calls are sufficient, so neither flag needs to be set. > + [...] > diff --git a/mm/gup.c b/mm/gup.c > index 199da99e8ffc..1aea48427879 100644 > --- a/mm/gup.c > +++ b/mm/gup.c [...] > @@ -1014,7 +1018,16 @@ static __always_inline long __get_user_pages_locke= d(struct task_struct *tsk, > =09=09BUG_ON(*locked !=3D 1); > =09} > =20 > -=09if (pages) > +=09/* > +=09 * FOLL_PIN and FOLL_GET are mutually exclusive. Traditional behavior > +=09 * is to set FOLL_GET if the caller wants pages[] filled in (but has > +=09 * carelessly failed to specify FOLL_GET), so keep doing that, but on= ly > +=09 * for FOLL_GET, not for the newer FOLL_PIN. > +=09 * > +=09 * FOLL_PIN always expects pages to be non-null, but no need to asser= t > +=09 * that here, as any failures will be obvious enough. > +=09 */ > +=09if (pages && !(flags & FOLL_PIN)) > =09=09flags |=3D FOLL_GET; Did you look at user that have pages and not FOLL_GET set ? I believe it would be better to first fix them to end up with FOLL_GET set and then error out if pages is !=3D NULL but nor FOLL_GET or FOLL_PIN is set. > =20 > =09pages_done =3D 0; > @@ -2373,24 +2402,9 @@ static int __gup_longterm_unlocked(unsigned long s= tart, int nr_pages, > =09return ret; > } > =20 > -/** > - * get_user_pages_fast() - pin user pages in memory > - * @start:=09starting user address > - * @nr_pages:=09number of pages from start to pin > - * @gup_flags:=09flags modifying pin behaviour > - * @pages:=09array that receives pointers to the pages pinned. > - *=09=09Should be at least nr_pages long. > - * > - * Attempt to pin user pages in memory without taking mm->mmap_sem. > - * If not successful, it will fall back to taking the lock and > - * calling get_user_pages(). > - * > - * Returns number of pages pinned. This may be fewer than the number > - * requested. If nr_pages is 0 or negative, returns 0. If no pages > - * were pinned, returns -errno. > - */ > -int get_user_pages_fast(unsigned long start, int nr_pages, > -=09=09=09unsigned int gup_flags, struct page **pages) > +static int internal_get_user_pages_fast(unsigned long start, int nr_page= s, > +=09=09=09=09=09unsigned int gup_flags, > +=09=09=09=09=09struct page **pages) Usualy function are rename to _old_func_name ie add _ in front. So here it would become _get_user_pages_fast but i know some people don't like that as sometimes we endup with ___function_overloaded :) > { > =09unsigned long addr, len, end; > =09int nr =3D 0, ret =3D 0; > @@ -2435,4 +2449,215 @@ int get_user_pages_fast(unsigned long start, int = nr_pages, [...] > +/** > + * pin_user_pages_remote() - pin pages for (typically) use by Direct IO,= and > + * return the pages to the user. Not a fan of (typically) maybe: pin_user_pages_remote() - pin pages of a remote process (task !=3D current) I think here the remote part if more important that DIO. Remote is use by other thing that DIO. > + * > + * Nearly the same as get_user_pages_remote(), except that FOLL_PIN is s= et. See > + * get_user_pages_remote() for documentation on the function arguments, = because > + * the arguments here are identical. > + * > + * FOLL_PIN means that the pages must be released via put_user_page(). P= lease > + * see Documentation/vm/pin_user_pages.rst for details. > + * > + * This is intended for Case 1 (DIO) in Documentation/vm/pin_user_pages.= rst. It > + * is NOT intended for Case 2 (RDMA: long-term pins). > + */ > +long pin_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm= , > +=09=09=09 unsigned long start, unsigned long nr_pages, > +=09=09=09 unsigned int gup_flags, struct page **pages, > +=09=09=09 struct vm_area_struct **vmas, int *locked) > +{ > +=09/* FOLL_GET and FOLL_PIN are mutually exclusive. */ > +=09if (WARN_ON_ONCE(gup_flags & FOLL_GET)) > +=09=09return -EINVAL; > + > +=09gup_flags |=3D FOLL_TOUCH | FOLL_REMOTE | FOLL_PIN; > + > +=09return __get_user_pages_locked(tsk, mm, start, nr_pages, pages, vmas, > +=09=09=09=09 locked, gup_flags); > +} > +EXPORT_SYMBOL(pin_user_pages_remote); > + > +/** > + * pin_longterm_pages_remote() - pin pages for (typically) use by Direct= IO, and > + * return the pages to the user. I think you copy pasted this from pin_user_pages_remote() :) > + * > + * Nearly the same as get_user_pages_remote(), but note that FOLL_TOUCH = is not > + * set, and FOLL_PIN and FOLL_LONGTERM are set. See get_user_pages_remot= e() for > + * documentation on the function arguments, because the arguments here a= re > + * identical. > + * > + * FOLL_PIN means that the pages must be released via put_user_page(). P= lease > + * see Documentation/vm/pin_user_pages.rst for further details. > + * > + * FOLL_LONGTERM means that the pages are being pinned for "long term" u= se, > + * typically by a non-CPU device, and we cannot be sure that waiting for= a > + * pinned page to become unpin will be effective. > + * > + * This is intended for Case 2 (RDMA: long-term pins) in > + * Documentation/vm/pin_user_pages.rst. > + */ > +long pin_longterm_pages_remote(struct task_struct *tsk, struct mm_struct= *mm, > +=09=09=09 unsigned long start, unsigned long nr_pages, > +=09=09=09 unsigned int gup_flags, struct page **pages, > +=09=09=09 struct vm_area_struct **vmas, int *locked) > +{ > +=09/* FOLL_GET and FOLL_PIN are mutually exclusive. */ > +=09if (WARN_ON_ONCE(gup_flags & FOLL_GET)) > +=09=09return -EINVAL; > + > +=09/* > +=09 * FIXME: as noted in the get_user_pages_remote() implementation, it > +=09 * is not yet possible to safely set FOLL_LONGTERM here. FOLL_LONGTER= M > +=09 * needs to be set, but for now the best we can do is a "TODO" item. > +=09 */ > +=09gup_flags |=3D FOLL_REMOTE | FOLL_PIN; Wouldn't it be better to not add pin_longterm_pages_remote() until it can be properly implemented ?