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

[KOSAKI Motohiro]

Hi

Thanks for great works.


> SUMMARY
> =======
> The patch decreases the number of major faults from 50 to 3 during 10% cache hot reads.
> 
> 
> SCENARIO
> ========
> The test scenario is to do 100000 pread(size=110 pages, offset=(i*100) pages),
> where 10% of the pages will be activated:
> 
>         for i in `seq 0 100 10000000`; do echo $i 110;  done > pattern-hot-10
>         iotrace.rb --load pattern-hot-10 --play /b/sparse


Which can I download iotrace.rb?


> and monitor /proc/vmstat during the time. The test box has 2G memory.
> 
> 
> ANALYZES
> ========
> 
> I carried out two runs on fresh booted console mode 2.6.29 with the VM_EXEC
> patch, and fetched the vmstat numbers on
> 
> (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
> 
>         nr_mapped   nr_active_file nr_inactive_file       pgmajfault     pgdeactivate           pgfree
> begin:       2481             2237             8694              630                0           574299
> end:          275           231976           233914              633           776271         20933042
> restore:      370           232154           234524              691           777183         20958453
> 
> begin:       2434             2237             8493              629                0           574195
> end:          284           231970           233536              632           771918         20896129
> restore:      399           232218           234789              690           774526         20957909
> 
> and another run on 2.6.30-rc4-mm with the VM_EXEC logic disabled:

I don't think it is proper comparision.
you need either following comparision. otherwise we insert many guess into the analysis.

 - 2.6.29 with and without VM_EXEC patch
 - 2.6.30-rc4-mm with and without VM_EXEC patch


> 
> begin:       2479             2344             9659              210                0           579643
> end:          284           232010           234142              260           772776         20917184
> restore:      379           232159           234371              301           774888         20967849
> 
> The 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 :-)
> 
> - 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.
> 
> - when active:inactive file lru size reaches 1:1, their scan rates is 1:20.8
>   under 10% cache hot IO. (computed with formula Dpgdeactivate:Dpgfree)
>   That roughly means the active mmap pages get 20.8 more chances to get
>   re-referenced to stay in memory.
> 
> - 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.)

I'm surprised this.
Why your patch don't protect mapped page from streaming io?

I strongly hope reproduce myself, please teach me reproduce way.





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