linux-kernel - Re: [PATCH 0/9] Add apply_to_page_range

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Date:	Thu, 27 Jan 2011 16:18:17 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Haavard Skinnemoen <hskinnemoen@...el.com>,
	Linux-MM <linux-mm@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Nick Piggin <npiggin@...nel.dk>,
	Xen-devel <xen-devel@...ts.xensource.com>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
Subject: Re: [PATCH 0/9] Add apply_to_page_range_batch() and use it

On Mon, 24 Jan 2011 14:55:58 -0800
Jeremy Fitzhardinge <jeremy@...p.org> wrote:

> From: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
> 
> I'm proposing this series for 2.6.39.
> 
> We've had apply_to_page_range() for a while, which is a general way to
> apply a function to ptes across a range of addresses - including
> allocating any missing parts of the pagetable as needed.  This logic
> is replicated in a number of places throughout the kernel, but it
> hasn't been widely replaced by this function, partly because of
> concerns about the overhead of calling the function once per pte.
> 
> This series adds apply_to_page_range_batch() (and reimplements
> apply_to_page_range() in terms of it), which calls the pte operation
> function once per pte page, moving the inner loop into the callback
> function.
> 
> apply_to_page_range(_batch) also calls its callback with lazy mmu
> updates enabled, which allows batching of the operations in
> environments where this is beneficial (ie, virtualization).  The only
> caveat this introduces is callbacks can't expect to immediately see
> the effects of the pte updates in memory.
> 
> Since this is effectively identical to the code in lib/ioremap.c and
> mm/vmalloc.c (twice!), I replace their open-coded variants.  I'm sure
> there are others places in the kernel which could do with this (I only
> stumbled over ioremap by accident).
> 
> I also add a minor optimisation to vunmap_page_range() to use a
> plain pte_clear() rather than the more expensive and unnecessary
> ptep_get_and_clear().
> 
> Jeremy Fitzhardinge (9):
>   mm: remove unused "token" argument from apply_to_page_range callback.
>   mm: add apply_to_page_range_batch()
>   ioremap: use apply_to_page_range_batch() for ioremap_page_range()
>   vmalloc: use plain pte_clear() for unmaps
>   vmalloc: use apply_to_page_range_batch() for vunmap_page_range()
>   vmalloc: use apply_to_page_range_batch() for
>     vmap_page_range_noflush()
>   vmalloc: use apply_to_page_range_batch() in alloc_vm_area()
>   xen/mmu: use apply_to_page_range_batch() in
>     xen_remap_domain_mfn_range()
>   xen/grant-table: use apply_to_page_range_batch()
> 
>  arch/x86/xen/grant-table.c |   30 +++++----
>  arch/x86/xen/mmu.c         |   18 +++--
>  include/linux/mm.h         |    9 ++-
>  lib/ioremap.c              |   85 +++++++------------------
>  mm/memory.c                |   57 ++++++++++++-----
>  mm/vmalloc.c               |  150 ++++++++++++--------------------------------
>  6 files changed, 140 insertions(+), 209 deletions(-)

That all looks good to me.
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