linux-kselftest.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: John Hubbard <jhubbard@nvidia.com>
To: Ira Weiny <ira.weiny@intel.com>
Cc: "Andrew Morton" <akpm@linux-foundation.org>,
	"Al Viro" <viro@zeniv.linux.org.uk>,
	"Alex Williamson" <alex.williamson@redhat.com>,
	"Benjamin Herrenschmidt" <benh@kernel.crashing.org>,
	"Björn Töpel" <bjorn.topel@intel.com>,
	"Christoph Hellwig" <hch@infradead.org>,
	"Dan Williams" <dan.j.williams@intel.com>,
	"Daniel Vetter" <daniel@ffwll.ch>,
	"Dave Chinner" <david@fromorbit.com>,
	"David Airlie" <airlied@linux.ie>,
	"David S . Miller" <davem@davemloft.net>,
	"Jan Kara" <jack@suse.cz>, "Jason Gunthorpe" <jgg@ziepe.ca>,
	"Jens Axboe" <axboe@kernel.dk>,
	"Jonathan Corbet" <corbet@lwn.net>,
	"Jérôme Glisse" <jglisse@redhat.com>,
	"Magnus Karlsson" <magnus.karlsson@intel.com>,
	"Mauro Carvalho Chehab" <mchehab@kernel.org>,
	"Michael Ellerman" <mpe@ellerman.id.au>,
	"Michal Hocko" <mhocko@suse.com>,
	"Mike Kravetz" <mike.kravetz@oracle.com>,
	"Paul Mackerras" <paulus@samba.org>,
	"Shuah Khan" <shuah@kernel.org>,
	"Vlastimil Babka" <vbabka@suse.cz>,
	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 <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 05/19] mm/gup: introduce pin_user_pages*() and FOLL_PIN
Date: Thu, 31 Oct 2019 16:43:16 -0700	[thread overview]
Message-ID: <f37f7727-4e19-2488-4db8-91feb72ace12@nvidia.com> (raw)
In-Reply-To: <20191031231503.GF14771@iweiny-DESK2.sc.intel.com>

On 10/31/19 4:15 PM, Ira Weiny wrote:
> On Wed, Oct 30, 2019 at 03:49:16PM -0700, John Hubbard wrote:
...
>> + * FOLL_PIN indicates that a special kind of tracking (not just page->_refcount,
>> + * but an additional pin counting system) will be invoked. This is intended for
>> + * anything that gets a page reference and then touches page data (for example,
>> + * Direct IO). This lets the filesystem know that some non-file-system entity is
>> + * potentially changing the pages' data. In contrast to FOLL_GET (whose pages
>> + * are released via put_page()), FOLL_PIN pages must be released, ultimately, by
>> + * a call to put_user_page().
>> + *
>> + * FOLL_PIN is similar to FOLL_GET: both of these pin pages. They use different
>> + * and separate refcounting mechanisms, however, and that means that each has
>> + * its own acquire and release mechanisms:
>> + *
>> + *     FOLL_GET: get_user_pages*() to acquire, and put_page() to release.
>> + *
>> + *     FOLL_PIN: pin_user_pages*() or pin_longterm_pages*() to acquire, and
>> + *               put_user_pages to release.
>> + *
>> + * FOLL_PIN and FOLL_GET are mutually exclusive.
> 
> You mean the flags are mutually exclusive for any single call, correct?
> Because my first thought was that you meant that a page which was pin'ed can't
> be "got".  Which I don't think is true or necessary...

Yes, you are correct. And yes you can absolutely mix get_user_pages() and 
pin_user_pages() calls on the same page(s).

OK, I'll change the wording to "mutually exclusive for a given function call".

> 
>> + *
>> + * Please see Documentation/vm/pin_user_pages.rst for more information.
> 
> NIT: I think we should include this file as part of this patch...

heh. I kept hopping back and forth on this, because I've seen other patchsets that
often put Documentation/ into its own patch. But you're right, of course: it's
not right to refer to items that are not here until a later patch. I'll merge
patch 19 into this one, then.

...
>> @@ -1603,11 +1630,25 @@ static __always_inline long __gup_longterm_locked(struct task_struct *tsk,
>>   * and mm being operated on are the current task's and don't allow
>>   * passing of a locked parameter.  We also obviously don't pass
>>   * FOLL_REMOTE in here.
>> + *
>> + * A note on gup_flags: FOLL_PIN should only be set internally by the
>> + * pin_user_page*() and pin_longterm_*() APIs, never directly by the caller.
>> + * That's in order to help avoid mismatches when releasing pages:
>> + * get_user_pages*() pages must be released via put_page(), while
>> + * pin_user_pages*() pages must be released via put_user_page().
> 
> Rather than put this here should we put it next to the definition of FOLL_PIN?
> Because now we have this text 2x...  :-/
> 

OK, I'll move it up next to FOLL_PIN, and get rid of the 2x places in gup.c


...
>> +long pin_longterm_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
>> +			       unsigned long start, unsigned long nr_pages,
>> +			       unsigned int gup_flags, struct page **pages,
>> +			       struct vm_area_struct **vmas, int *locked)
>> +{
>> +	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
>> +	if (WARN_ON_ONCE(gup_flags & FOLL_GET))
>> +		return -EINVAL;
>> +
>> +	/*
>> +	 * FIXME: as noted in the get_user_pages_remote() implementation, it
>> +	 * is not yet possible to safely set FOLL_LONGTERM here. FOLL_LONGTERM
>> +	 * needs to be set, but for now the best we can do is a "TODO" item.
>> +	 */
> 
> Wait?  Why can't we set FOLL_LONGTERM here?  pin_* are new calls which are not
> used yet right?

Nope, not quite! See patch #14 ("vfio, mm: pin_longterm_pages (FOLL_PIN) and 
put_user_page() conversion"), in which I'm converting an existing 
get_user_pages_remote() caller.

> 
> You set it in the other new pin_* functions?
> 

Yes I did. Because those work already in their gup() counterparts.

thanks,

John Hubbard
NVIDIA

  reply	other threads:[~2019-10-31 23:43 UTC|newest]

Thread overview: 47+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-30 22:49 [PATCH 00/19] mm/gup: track dma-pinned pages: FOLL_PIN, FOLL_LONGTERM John Hubbard
2019-10-30 22:49 ` [PATCH 01/19] mm/gup: pass flags arg to __gup_device_* functions John Hubbard
2019-10-31 18:18   ` Ira Weiny
2019-10-30 22:49 ` [PATCH 02/19] mm/gup: factor out duplicate code from four routines John Hubbard
2019-10-31 18:35   ` Ira Weiny
2019-10-31 18:43     ` John Hubbard
2019-10-31 21:09       ` Ira Weiny
2019-10-31 22:01         ` John Hubbard
2019-10-30 22:49 ` [PATCH 03/19] goldish_pipe: rename local pin_user_pages() routine John Hubbard
2019-10-31 18:36   ` Ira Weiny
2019-10-30 22:49 ` [PATCH 04/19] media/v4l2-core: set pages dirty upon releasing DMA buffers John Hubbard
2019-10-30 22:49 ` [PATCH 05/19] mm/gup: introduce pin_user_pages*() and FOLL_PIN John Hubbard
2019-10-31 23:15   ` Ira Weiny
2019-10-31 23:43     ` John Hubbard [this message]
2019-10-30 22:49 ` [PATCH 06/19] goldish_pipe: convert to pin_user_pages() and put_user_page() John Hubbard
2019-10-30 22:49 ` [PATCH 07/19] infiniband: set FOLL_PIN, FOLL_LONGTERM via pin_longterm_pages*() John Hubbard
2019-10-31 23:25   ` Ira Weiny
2019-10-31 23:49     ` John Hubbard
2019-10-30 22:49 ` [PATCH 08/19] mm/process_vm_access: set FOLL_PIN via pin_user_pages_remote() John Hubbard
2019-10-31 23:35   ` Ira Weiny
2019-10-31 23:46     ` John Hubbard
2019-10-30 22:49 ` [PATCH 09/19] drm/via: set FOLL_PIN via pin_user_pages_fast() John Hubbard
2019-10-31 23:36   ` Ira Weiny
2019-11-04 18:10     ` Daniel Vetter
2019-11-04 19:20       ` John Hubbard
2019-11-05  9:49         ` Daniel Vetter
2019-11-05 18:16           ` John Hubbard
2019-10-30 22:49 ` [PATCH 10/19] fs/io_uring: set FOLL_PIN via pin_user_pages() John Hubbard
2019-10-31 23:37   ` Ira Weiny
2019-11-01 14:49   ` Jens Axboe
2019-10-30 22:49 ` [PATCH 11/19] net/xdp: " John Hubbard
2019-10-31 23:37   ` Ira Weiny
2019-11-02 11:01   ` Björn Töpel
2019-10-30 22:49 ` [PATCH 12/19] mm/gup: track FOLL_PIN pages John Hubbard
2019-10-30 22:49 ` [PATCH 13/19] media/v4l2-core: pin_longterm_pages (FOLL_PIN) and put_user_page() conversion John Hubbard
2019-10-31 23:38   ` Ira Weiny
2019-10-30 22:49 ` [PATCH 14/19] vfio, mm: " John Hubbard
2019-10-30 23:05   ` John Hubbard
2019-10-30 22:49 ` [PATCH 15/19] powerpc: book3s64: convert to pin_longterm_pages() and put_user_page() John Hubbard
2019-10-30 22:49 ` [PATCH 16/19] mm/gup_benchmark: support pin_user_pages() and related calls John Hubbard
2019-10-30 22:49 ` [PATCH 17/19] selftests/vm: run_vmtests: invoke gup_benchmark with basic FOLL_PIN coverage John Hubbard
2019-10-30 22:49 ` [PATCH 18/19] mm/gup: remove support for gup(FOLL_LONGTERM) John Hubbard
2019-10-30 22:49 ` [PATCH 19/19] Documentation/vm: add pin_user_pages.rst John Hubbard
2019-10-31 23:49   ` Ira Weiny
2019-10-31 23:53     ` John Hubbard
2019-11-01  0:48     ` John Hubbard
2019-11-03 19:53   ` John Hubbard

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=f37f7727-4e19-2488-4db8-91feb72ace12@nvidia.com \
    --to=jhubbard@nvidia.com \
    --cc=airlied@linux.ie \
    --cc=akpm@linux-foundation.org \
    --cc=alex.williamson@redhat.com \
    --cc=axboe@kernel.dk \
    --cc=benh@kernel.crashing.org \
    --cc=bjorn.topel@intel.com \
    --cc=bpf@vger.kernel.org \
    --cc=corbet@lwn.net \
    --cc=dan.j.williams@intel.com \
    --cc=daniel@ffwll.ch \
    --cc=davem@davemloft.net \
    --cc=david@fromorbit.com \
    --cc=dri-devel@lists.freedesktop.org \
    --cc=hch@infradead.org \
    --cc=ira.weiny@intel.com \
    --cc=jack@suse.cz \
    --cc=jgg@ziepe.ca \
    --cc=jglisse@redhat.com \
    --cc=kvm@vger.kernel.org \
    --cc=linux-block@vger.kernel.org \
    --cc=linux-doc@vger.kernel.org \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-kselftest@vger.kernel.org \
    --cc=linux-media@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=linux-rdma@vger.kernel.org \
    --cc=linuxppc-dev@lists.ozlabs.org \
    --cc=magnus.karlsson@intel.com \
    --cc=mchehab@kernel.org \
    --cc=mhocko@suse.com \
    --cc=mike.kravetz@oracle.com \
    --cc=mpe@ellerman.id.au \
    --cc=netdev@vger.kernel.org \
    --cc=paulus@samba.org \
    --cc=shuah@kernel.org \
    --cc=vbabka@suse.cz \
    --cc=viro@zeniv.linux.org.uk \
    --subject='Re: [PATCH 05/19] mm/gup: introduce pin_user_pages*() and FOLL_PIN' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).