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

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Message-ID: <20190123183353.GA15768@ziepe.ca>
Date:   Wed, 23 Jan 2019 11:33:53 -0700
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Davidlohr Bueso <dave@...olabs.net>
Cc:     akpm@...ux-foundation.org, 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 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?

Regards,
Jason