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SubjectRe: si_swapinfo export
Well, in my personal case it is some 'memory pressure service' for 
virtual machines in xen environment.

It check about 1-2 times per second memory state and report it to
management software outside VM. Right now this is userspace program,
which reads /proc/meminfo and sends it via xenstore (interdomain
communication system) to management domain. It works fine, but we need
to do double int-str conversion (/proc/meminfo do itoa, our daemon sens
this to control domain, daemon in control domain do atoi and math to get
right memory value). This is very inefficient, especially when we talks
about bunch of VM per host.

kernel module can do math internally with ints, not with strings (no
conversion at all) - this will save pretty much time (my calculation is
about one-two of CPU time per day for every virtualization host with
about 50-100 active VMs.

The information I needs is amount of 'really free' memory. We calculate
it as (roughly) as MemFree+Buffers+Cached+(SwapTotal-SwapFree), and our
management system trying to keep this value within expected values (f.e.
within interval 128-256Mb). This allows us to prevent VM's swapping and
allow VM to push to swap really rare used pages (and their place
actually used for caching).


On 02.09.2011 23:53, Valdis.Kletnieks@vt.edu wrote:
> On Fri, 02 Sep 2011 19:41:29 +0400, George Shuklin said:
>> Good day.
>>
>> Why si_swapinfo (from include/linux/swap.h) is not marked as
>> EXPORT_SYMBOL_GPL? It's kinda hard to gain information about memory in
>> module.
> Use case? What information exactly are you trying to get in the module, and
> equally important, why? More likely, what you *actually* want isn't the
> information, it's a new API (or using an existing one you didn't even know was
> there) :)
>


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