Re: [PATCH] mm: moving dirty pages balancing to pdfludh entirely

[Nikita Danilov <nikita@clusterfs.com>]

Ananiev, Leonid I writes:
 > >From Leonid Ananiev

Hello,

 > 
 > Moving dirty pages balancing from user to kernel thread pdfludh entirely
 > reduces extra long write(2) latencies, increases performance.
 > 

[...]

 > 	The benchmarks IOzone and Sysbench for file size 50% and 120% of
 > RAM size on Pentium4, Xeon, Itanium have reported write and mix
 > throughput increasing about 25%. The described Iozone > 0.1 sec write(2)

Results are impressive.

Wouldn't this interfere with current->backing_dev_info logic? This field
is set by __generic_file_aio_write_nolock() and checked by
may_write_to_queue() to force heavy writes to do more pageout. Maybe
pdflush threads should set this field too?

 > latencies are deleted. The condition writeback_in_progress() is tested
 > earlier now. As a result extra pdflush works are not created and number
 > of context switches increasing is inside variation limites.

Nikita.