netdev - RE: [PATCH 0/3] Add gup fast + longterm and use it in HFI1

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Date:   Mon, 11 Feb 2019 22:40:02 +0000
From:   "Weiny, Ira" <ira.weiny@...el.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
CC:     "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "Marciniszyn, Mike" <mike.marciniszyn@...el.com>,
        "Dalessandro, Dennis" <dennis.dalessandro@...el.com>,
        Doug Ledford <dledford@...hat.com>,
        "Andrew Morton" <akpm@...ux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        "Williams, Dan J" <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 01:42:57PM -0800, Ira Weiny wrote:
> > 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?!?!
> 
> Many drivers do this, the 'doorbell' is a PCI -> CPU thing of some sort

My surprise is why does _userspace_ allocate this memory?

> 
> > 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?
> 
> It needs to use umem like all the other drivers on this path.
> Otherwise it doesn't get the page pinning logic right

Not sure what you mean regarding the pinning logic?

> 
> There is also something else rotten with these longterm callsites, they seem
> to have very different ideas how to handle RLIMIT_MEMLOCK.
> 
> ie vfio doesn't even touch pinned_vm.. and rdma is applying
> RLIMIT_MEMLOCK to mm->pinned_vm, while vfio is using locked_vm.. No
> idea which is right, but they should be the same, and this pattern should
> probably be in core code someplace.

Neither do I.  But AFAIK pinned_vm is a subset of locked_vm.

So should we be accounting both of the counters?

Ira