[PATCH] 2.2.17pre7 VM enhancement Re: I/O performance on 2.4.0-test2

[Marcelo Tosatti]

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On Sun, 25 Jun 2000, Jens Axboe wrote:

<snip> 

> 
> I also did a dbench run.
> 
> 2.2.17-pre6
> 
> burns:/opt/software/testing # ./dbench 48
> 48 clients started
> Throughput 12.84 MB/sec (NB=16.0499 MB/sec  128.4 MBit/sec)
> 
> 2.4.0-test2-ac1
> 
> burns:/opt/software/testing # ./dbench 48
> 48 clients started
> Throughput 30.6317 MB/sec (NB=38.2896 MB/sec  306.317 MBit/sec)
> 
> The 2.2 results are very disappointing here, the last time I checked
> 2.2 dbench results were in the ~24MB/sec range.

In 2.2.17pre7, try_to_free_buffers() was only waking up kflushd in case
sync_page_buffers() failed to sync the dirty buffers of a page. 

With the attached patch, try_to_free_buffers() wakes up kflushd if the
percentage of dirty memory is high, independant of sync_page_buffers
failing or not. The patch also modifies do_try_to_free_pages to print a
"VM: do_try_to_free_pages failed..." only when _no_ progress is made. 

Testing dbench with 48 processes on one of the test machines around here
(IDE disk), I've got 13MB/sec with 2.2.17pre7, 17MB/sec with 2.2.17pre7 +
the attached patch, and 23MB/s with 2.4.0-t1-ac22. 

Jens, could you please try to run dbench with this patch on your machine
and report us results? Thanks a lot. 

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