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