Change in default vm_dirty_ratio

[Tim Chen <tim.c.chen@linux.intel.com>]

Andrew,

The default vm_dirty_ratio changed from 40 to 10
for the 2.6.22-rc kernels in this patch:
 
http://git.kernel.org/?
p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=07db59bd6b0f279c31044cba6787344f63be87ea;hp=de46c33745f5e2ad594c72f2cf5f490861b16ce1

IOZone write drops by about 60% when test file size is 50 percent of
memory.  Rand-write drops by 90%. 

Is there a good reason for turning down the default dirty ratio?
How will it help for most cases?  Intuitively, it seems like 
a less aggressive writeback will have better performance.

Thanks.

Tim
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