linux-kernel - Re: [PATCH 0/3] Add gup fast + longterm and use it in HFI1

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Date:   Mon, 11 Feb 2019 13:42:57 -0800
From:   Ira Weiny <ira.weiny@...el.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Daniel Borkmann <daniel@...earbox.net>,
        netdev@...r.kernel.org,
        Mike Marciniszyn <mike.marciniszyn@...el.com>,
        Dennis Dalessandro <dennis.dalessandro@...el.com>,
        Doug Ledford <dledford@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH 0/3] Add gup fast + longterm and use it in HFI1

On Mon, Feb 11, 2019 at 01:47:10PM -0700, Jason Gunthorpe wrote:
> On Mon, Feb 11, 2019 at 12:34:17PM -0800, Davidlohr Bueso wrote:
> > On Mon, 11 Feb 2019, ira.weiny@...el.com wrote:
> > > Ira Weiny (3):
> > >  mm/gup: Change "write" parameter to flags
> > >  mm/gup: Introduce get_user_pages_fast_longterm()
> > >  IB/HFI1: Use new get_user_pages_fast_longterm()
> > 
> > Out of curiosity, are you planning on having all rdma drivers
> > use get_user_pages_fast_longterm()? Ie:
> > 
> > hw/mthca/mthca_memfree.c:       ret = get_user_pages_fast(uaddr & PAGE_MASK, 1, FOLL_WRITE, pages);
> 
> This one is certainly a mistake - this should be done with a umem.

It looks like this is mapping a page allocated by user space for a doorbell?!?!
And that this is supporting the old memory free cards.  I remember that these
cards used system memory instead of memory on the cards but why it expects user
space to allocate that memory and how it all works is way too old for me to
even try to remember.

This does not seem to be allocating memory regions.  Jason, do you want a patch
to just convert these calls and consider it legacy code?

Ira

> 
> Jason