From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-nvdimm-bounces@lists.01.org>
Received: from mail-oi1-x243.google.com (mail-oi1-x243.google.com
 [IPv6:2607:f8b0:4864:20::243])
 (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits))
 (No client certificate requested)
 by ml01.01.org (Postfix) with ESMTPS id CAE4A2129604D
 for <linux-nvdimm@lists.01.org>; Wed, 12 Jun 2019 11:50:03 -0700 (PDT)
Received: by mail-oi1-x243.google.com with SMTP id t76so12480272oih.4
 for <linux-nvdimm@lists.01.org>; Wed, 12 Jun 2019 11:50:03 -0700 (PDT)
MIME-Version: 1.0
References: <20190606014544.8339-1-ira.weiny@intel.com>
 <20190606104203.GF7433@quack2.suse.cz>
 <20190606195114.GA30714@ziepe.ca>
 <20190606222228.GB11698@iweiny-DESK2.sc.intel.com>
 <20190607103636.GA12765@quack2.suse.cz> <20190607121729.GA14802@ziepe.ca>
 <20190607145213.GB14559@iweiny-DESK2.sc.intel.com>
 <20190612102917.GB14578@quack2.suse.cz>
In-Reply-To: <20190612102917.GB14578@quack2.suse.cz>
From: Dan Williams <dan.j.williams@intel.com>
Date: Wed, 12 Jun 2019 11:49:52 -0700
Message-ID: <CAPcyv4jSyTjC98UsWb3-FnZekV0oyboiSe9n1NYDC2TSKAqiqw@mail.gmail.com>
Subject: Re: [PATCH RFC 00/10] RDMA/FS DAX truncate proposal
List-Unsubscribe: <https://lists.01.org/mailman/options/linux-nvdimm>,
 <mailto:linux-nvdimm-request@lists.01.org?subject=unsubscribe>
List-Archive: <http://lists.01.org/pipermail/linux-nvdimm/>
List-Post: <mailto:linux-nvdimm@lists.01.org>
List-Help: <mailto:linux-nvdimm-request@lists.01.org?subject=help>
List-Subscribe: <https://lists.01.org/mailman/listinfo/linux-nvdimm>,
 <mailto:linux-nvdimm-request@lists.01.org?subject=subscribe>
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Errors-To: linux-nvdimm-bounces@lists.01.org
Sender: "Linux-nvdimm" <linux-nvdimm-bounces@lists.01.org>
To: Jan Kara <jack@suse.cz>
Cc: Theodore Ts'o <tytso@mit.edu>, linux-nvdimm <linux-nvdimm@lists.01.org>, Dave Chinner <david@fromorbit.com>, Jeff Layton <jlayton@kernel.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Matthew Wilcox <willy@infradead.org>, linux-xfs <linux-xfs@vger.kernel.org>, Jason Gunthorpe <jgg@ziepe.ca>, =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= <jglisse@redhat.com>, John Hubbard <jhubbard@nvidia.com>, linux-fsdevel <linux-fsdevel@vger.kernel.org>, Andrew Morton <akpm@linux-foundation.org>, linux-ext4 <linux-ext4@vger.kernel.org>, Linux MM <linux-mm@kvack.org>
List-ID: <linux-nvdimm@lists.01.org>

On Wed, Jun 12, 2019 at 3:29 AM Jan Kara <jack@suse.cz> wrote:
>
> On Fri 07-06-19 07:52:13, Ira Weiny wrote:
> > On Fri, Jun 07, 2019 at 09:17:29AM -0300, Jason Gunthorpe wrote:
> > > On Fri, Jun 07, 2019 at 12:36:36PM +0200, Jan Kara wrote:
> > >
> > > > Because the pins would be invisible to sysadmin from that point on.
> > >
> > > It is not invisible, it just shows up in a rdma specific kernel
> > > interface. You have to use rdma netlink to see the kernel object
> > > holding this pin.
> > >
> > > If this visibility is the main sticking point I suggest just enhancing
> > > the existing MR reporting to include the file info for current GUP
> > > pins and teaching lsof to collect information from there as well so it
> > > is easy to use.
> > >
> > > If the ownership of the lease transfers to the MR, and we report that
> > > ownership to userspace in a way lsof can find, then I think all the
> > > concerns that have been raised are met, right?
> >
> > I was contemplating some new lsof feature yesterday.  But what I don't
> > think we want is sysadmins to have multiple tools for multiple
> > subsystems.  Or even have to teach lsof something new for every potential
> > new subsystem user of GUP pins.
>
> Agreed.
>
> > I was thinking more along the lines of reporting files which have GUP
> > pins on them directly somewhere (dare I say procfs?) and teaching lsof to
> > report that information.  That would cover any subsystem which does a
> > longterm pin.
>
> So lsof already parses /proc/<pid>/maps to learn about files held open by
> memory mappings. It could parse some other file as well I guess. The good
> thing about that would be that then "longterm pin" structure would just hold
> struct file reference. That would avoid any needs of special behavior on
> file close (the file reference in the "longterm pin" structure would make
> sure struct file and thus the lease stays around, we'd just need to make
> explicit lease unlock block until the "longterm pin" structure is freed).
> The bad thing is that it requires us to come up with a sane new proc
> interface for reporting "longterm pins" and associated struct file. Also we
> need to define what this interface shows if the pinned pages are in DRAM
> (either page cache or anon) and not on NVDIMM.

The anon vs shared detection case is important because a longterm pin
might be blocking a memory-hot-unplug operation if it is pinning
ZONE_MOVABLE memory, but I don't think we want DRAM vs NVDIMM to be an
explicit concern of the interface. For the anon / cached case I expect
it might be useful to put that communication under the memory-blocks
sysfs interface. I.e. a list of pids that are pinning that
memory-block from being hot-unplugged.
_______________________________________________
Linux-nvdimm mailing list
Linux-nvdimm@lists.01.org
https://lists.01.org/mailman/listinfo/linux-nvdimm