linux-kernel - Re: [PATCH v11 00/25] mm/gup: track dma-pinned pages: FOLL

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Message-ID: <20191223182446.GA28321@ziepe.ca>
Date:   Mon, 23 Dec 2019 14:24:46 -0400
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     John Hubbard <jhubbard@...dia.com>,
        Leon Romanovsky <leon@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Alex Williamson <alex.williamson@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Björn Töpel <bjorn.topel@...el.com>,
        Christoph Hellwig <hch@...radead.org>,
        Daniel Vetter <daniel@...ll.ch>,
        Dave Chinner <david@...morbit.com>,
        David Airlie <airlied@...ux.ie>,
        "David S . Miller" <davem@...emloft.net>,
        Ira Weiny <ira.weiny@...el.com>, Jan Kara <jack@...e.cz>,
        Jens Axboe <axboe@...nel.dk>, Jonathan Corbet <corbet@....net>,
        Jérôme Glisse <jglisse@...hat.com>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
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        Maor Gottlieb <maorg@...lanox.com>
Subject: Re: [PATCH v11 00/25] mm/gup: track dma-pinned pages: FOLL_PIN

On Fri, Dec 20, 2019 at 04:32:13PM -0800, Dan Williams wrote:

> > > There's already a limit, it's just a much larger one. :) What does "no limit"
> > > really mean, numerically, to you in this case?
> >
> > I guess I mean 'hidden limit' - hitting the limit and failing would
> > be managable.
> >
> > I think 7 is probably too low though, but we are not using 1GB huge
> > pages, only 2M..
> 
> What about RDMA to 1GB-hugetlbfs and 1GB-device-dax mappings?

I don't think the failing testing is doing that.

It is also less likely that 1GB regions will need multi-mapping, IMHO.

Jason