linux-kernel - Re: [PATCH v5 3/9] mm: Add write-protect and clean utilities for address space ranges

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Date:   Wed, 12 Jun 2019 04:23:50 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Thomas Hellström (VMware) 
        <thellstrom@...opensource.org>
Cc:     dri-devel@...ts.freedesktop.org,
        linux-graphics-maintainer@...are.com, pv-drivers@...are.com,
        linux-kernel@...r.kernel.org, nadav.amit@...il.com,
        Thomas Hellstrom <thellstrom@...are.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Will Deacon <will.deacon@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Rik van Riel <riel@...riel.com>,
        Minchan Kim <minchan@...nel.org>,
        Michal Hocko <mhocko@...e.com>,
        Huang Ying <ying.huang@...el.com>,
        Souptick Joarder <jrdr.linux@...il.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        linux-mm@...ck.org, Ralph Campbell <rcampbell@...dia.com>
Subject: Re: [PATCH v5 3/9] mm: Add write-protect and clean utilities for
 address space ranges

On Wed, Jun 12, 2019 at 08:42:37AM +0200, Thomas Hellström (VMware) wrote:
> From: Thomas Hellstrom <thellstrom@...are.com>
> 
> Add two utilities to a) write-protect and b) clean all ptes pointing into
> a range of an address space.
> The utilities are intended to aid in tracking dirty pages (either
> driver-allocated system memory or pci device memory).
> The write-protect utility should be used in conjunction with
> page_mkwrite() and pfn_mkwrite() to trigger write page-faults on page
> accesses. Typically one would want to use this on sparse accesses into
> large memory regions. The clean utility should be used to utilize
> hardware dirtying functionality and avoid the overhead of page-faults,
> typically on large accesses into small memory regions.

Please use EXPORT_SYMBOL_GPL, just like for apply_to_page_range and
friends.  Also in general new core functionality like this should go
along with the actual user, we don't need to repeat the hmm disaster.