linux-kernel - Re: [PATCH 1/7] mm: Add write-protect and clean utilities for address space ranges

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Date:   Wed, 18 Sep 2019 17:41:02 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Thomas Hellström (VMware) 
        <thomas_os@...pmail.org>
Cc:     linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-mm@...ck.org, pv-drivers@...are.com,
        linux-graphics-maintainer@...are.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>,
        Ralph Campbell <rcampbell@...dia.com>
Subject: Re: [PATCH 1/7] mm: Add write-protect and clean utilities for
 address space ranges

On Wed, Sep 18, 2019 at 02:59:08PM +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.
> 
> The added file "as_dirty_helpers.c" is initially listed as maintained by
> VMware under our DRM driver. If somebody would like it elsewhere,
> that's of course no problem.

After quick glance, it looks a lot as rmap code duplication. Why not
extend rmap_walk() interface instead to cover range of pages?

> 
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Matthew Wilcox <willy@...radead.org>
> Cc: Will Deacon <will.deacon@....com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Rik van Riel <riel@...riel.com>
> Cc: Minchan Kim <minchan@...nel.org>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Huang Ying <ying.huang@...el.com>
> Cc: Souptick Joarder <jrdr.linux@...il.com>
> Cc: "Jérôme Glisse" <jglisse@...hat.com>
> Cc: linux-mm@...ck.org
> Cc: linux-kernel@...r.kernel.org
> 
> Signed-off-by: Thomas Hellstrom <thellstrom@...are.com>
> Reviewed-by: Ralph Campbell <rcampbell@...dia.com> #v1
> ---
>  MAINTAINERS           |   1 +
>  include/linux/mm.h    |  13 +-
>  mm/Kconfig            |   3 +
>  mm/Makefile           |   1 +
>  mm/as_dirty_helpers.c | 392 ++++++++++++++++++++++++++++++++++++++++++
>  5 files changed, 409 insertions(+), 1 deletion(-)
>  create mode 100644 mm/as_dirty_helpers.c
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index c2d975da561f..b596c7cf4a85 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -5287,6 +5287,7 @@ T:	git git://people.freedesktop.org/~thomash/linux
>  S:	Supported
>  F:	drivers/gpu/drm/vmwgfx/
>  F:	include/uapi/drm/vmwgfx_drm.h
> +F:	mm/as_dirty_helpers.c

Emm.. No. Core MM functinality cannot belong to random driver.

-- 
 Kirill A. Shutemov