Re: [Intel-gfx] [PATCH v2 1/2] mm: Export nr_swap_pages

[Dave Gordon <david.s.gordon@intel.com>]

On 07/12/15 16:48, Johannes Weiner wrote:
> On Mon, Dec 07, 2015 at 02:48:12PM +0100, Michal Hocko wrote:
>> On Fri 04-12-15 15:58:53, Chris Wilson wrote:
>>> Some modules, like i915.ko, use swappable objects and may try to swap
>>> them out under memory pressure (via the shrinker). Before doing so, they
>>> want to check using get_nr_swap_pages() to see if any swap space is
>>> available as otherwise they will waste time purging the object from the
>>> device without recovering any memory for the system. This requires the
>>> nr_swap_pages counter to be exported to the modules.
>>
>> I guess it should be sufficient to change get_nr_swap_pages into a real
>> function and export it rather than giving the access to the counter
>> directly?
>
> What do you mean by "sufficient"? That is actually more work.
>
> It should be sufficient to just export the counter.
> _______________________________________________

Exporting random uncontrolled variables from the kernel to loaded 
modules is not really considered best practice. It would be preferable 
to provide an accessor function - which is just what the declaration 
says we have; the implementation as a static inline (and/or macro) is 
what causes the problem here.

.Dave.

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