Re: [Xen-devel] [PATCH 12 of 18] x86/mm: Make page_lock/unlock() in arch/x86/mm.c externally callable

[Tim Deegan <tim@xxxxxxx>]

At 02:47 -0500 on 08 Dec (1323312447), Andres Lagar-Cavilla wrote:
> This is necessary for a new consumer of page_lock/unlock to follow in
> the series.
> 
> Signed-off-by: Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx>

Nak, I'm afraid. 

These were OK as local functions but if they're going to be made
generally visible, they need clear comments describing what this
locking protects and what the discipline is for avoiding deadlocks.

Perhaps Jan or Keir can supply appropriate words.  The locking was
introduce in this cset:

    changeset:   17846:09dd5999401b
    user:        Keir Fraser <keir.fraser@xxxxxxxxxx>
    date:        Thu Jun 12 18:14:00 2008 +0100
    files:       xen/arch/x86/domain.c xen/arch/x86/domain_build.c
    xen/arch/x86/mm.c
    description:
    x86: remove use of per-domain lock from page table entry handling
    
    This change results in a 5% performance improvement for kernel builds
    on dual-socket quad-core systems (which is what I used for reference
    for both 32- and 64-bit). Along with that, the amount of time reported
    as spent in the kernel gets reduced by almost 25% (the fraction of
    time spent in the kernel is generally reported significantly higher
    under Xen than with a native kernel).
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>
    Signed-off-by: Keir Fraser <keir.fraser@xxxxxxxxxx>    

Tim.

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