linux-kernel - Re: [PATCH 1/6] mm: make mm->pinned

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Date:   Mon, 28 Jan 2019 13:10:56 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     Davidlohr Bueso <dave@...olabs.net>, dledford@...hat.com,
        jack@...e.de, ira.weiny@...el.com, linux-rdma@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Davidlohr Bueso <dbueso@...e.de>,
        Christoph Lameter <cl@...ux.com>, Jan Kara <jack@...e.cz>,
        Daniel Jordan <daniel.m.jordan@...cle.com>
Subject: Re: [PATCH 1/6] mm: make mm->pinned_vm an atomic64 counter

On Wed, 23 Jan 2019 11:33:53 -0700 Jason Gunthorpe <jgg@...pe.ca> wrote:

> On Mon, Jan 21, 2019 at 09:42:15AM -0800, Davidlohr Bueso wrote:
> > Taking a sleeping lock to _only_ increment a variable is quite the
> > overkill, and pretty much all users do this. Furthermore, some drivers
> > (ie: infiniband and scif) that need pinned semantics can go to quite
> > some trouble to actually delay via workqueue (un)accounting for pinned
> > pages when not possible to acquire it.
> > 
> > By making the counter atomic we no longer need to hold the mmap_sem
> > and can simply some code around it for pinned_vm users. The counter
> > is 64-bit such that we need not worry about overflows such as rdma
> > user input controlled from userspace.
> 
> I see a number of MM people Reviewed-by this so are we good to take
> this in the RDMA tree now?

Please do.