linux-kernel - Re: [RFC] mm: gup: add helper page_try_gup

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Message-ID: <20191104081317.GB22379@quack2.suse.cz>
Date:   Mon, 4 Nov 2019 09:13:17 +0100
From:   Jan Kara <jack@...e.cz>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     Hillf Danton <hdanton@...a.com>, linux-mm <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Vlastimil Babka <vbabka@...e.cz>, Jan Kara <jack@...e.cz>,
        Mel Gorman <mgorman@...e.de>,
        Jerome Glisse <jglisse@...hat.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Christoph Hellwig <hch@....de>,
        Jonathan Corbet <corbet@....net>
Subject: Re: [RFC] mm: gup: add helper page_try_gup_pin(page)

On Sun 03-11-19 22:09:03, John Hubbard wrote:
> On 11/3/19 8:34 PM, Hillf Danton wrote:
> > future, we have options for instance that gupers periodically release
> > their references and re-pin pages after data sync the same way as the
> > current flusher does.
> > 
> 
> That's one idea. I don't see it as viable, given the behavior of, say,
> a compute process running OpenCL jobs on a GPU that is connected via
> a network or Infiniband card--the idea of "pause" really looks more like
> "tear down the complicated multi-driver connection, writeback, then set it
> all up again", I suspect. (And if we could easily interrupt the job, we'd
> probably really be running with a page-fault-capable GPU plus and IB card
> that does ODP, plus HMM, and we wouldn't need to gup-pin anyway...)
> 
> Anyway, this is not amenable to quick fixes, because the problem is
> a couple of missing design pieces. Which we're working on putting in.
> But meanwhile, smaller changes such as this one are just going to move
> the problems to different places, rather than solving them. So it's best
> not to do that.

Yeah, fully agreed here. Quick half baked fixes will make the current messy
situation even worse...

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR