Re: [PATCH 2/3] vmscan: make mapped executable pages the first class citizen

[Nai Xia <nai.xia@gmail.com>]

On Mon, Jun 8, 2009 at 11:34 PM, Christoph
Lameter<cl@linux-foundation.org> wrote:
> On Mon, 8 Jun 2009, Wu Fengguang wrote:
>
>> 1.2) test scenario
>>
>> - nfsroot gnome desktop with 512M physical memory
>> - run some programs, and switch between the existing windows
>>   after starting each new program.
>
> Is there a predefined sequence or does this vary between tests? Scripted?
>
> What percentage of time is saved in the test after due to the
> modifications?
> Around 20%?

I think measuring the percentage of saved time may not be a good idea.
The major underlying  factor for time of swithing GUI windows may vary
application to application, distribution to distribution and machine to
machine. It's not reproducable.
I am having a ridiculous timing for swithing from any window to window
of slickedit, because of its damn slow redrawing method.
I bet this patch will gain at most 1% on timing for this case. :)

>
>> (1) begin:     shortly after the big read IO starts;
>> (2) end:       just before the big read IO stops;
>> (3) restore:   the big read IO stops and the zsh working set restored
>> (4) restore X: after IO, switch back and forth between the urxvt and firefox
>>                windows to restore their working set.
>
> Any action done on the firefox sessions? Or just switch to a firefox
> session that needs to redraw?
>
>> The above console numbers show that
>>
>> - The startup pgmajfault of 2.6.30-rc4-mm is merely 1/3 that of 2.6.29.
>>   I'd attribute that improvement to the mmap readahead improvements :-)
>
> So there are other effects,,, You not measuring the effect only this
> patchset?
>
>> - The pgmajfault increment during the file copy is 633-630=3 vs 260-210=50.
>>   That's a huge improvement - which means with the VM_EXEC protection logic,
>>   active mmap pages is pretty safe even under partially cache hot streaming IO.
>
> Looks good.
>
>> - The absolute nr_mapped drops considerably to 1/9 during the big IO, and the
>>   dropped pages are mostly inactive ones. The patch has almost no impact in
>>   this aspect, that means it won't unnecessarily increase memory pressure.
>>   (In contrast, your 20% mmap protection ratio will keep them all, and
>>   therefore eliminate the extra 41 major faults to restore working set
>>   of zsh etc.)
>
> Good.
>
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