Re: 2.6.36 io bring the system to its knees

[Dimitrios Apostolou]

Hello, 

On Sun, 31 Oct 2010 09:51:32 +0800, Wu Fengguang wrote:
> It may also help to lower the dirty ratio.
> 
> echo 5 > /proc/sys/vm/dirty_ratio
> 
> Memory pressure + heavy write can easily hurt responsiveness.
> 
> - eats up to 20% (the default value for dirty_ratio) memory with dirty
>   pages and hence increase the memory pressure and number of swap IO

My experience has been different with that. Wouldn't it make more sense 
to _increase_ dirty_ratio (to 50 lets say) and at the same time decrease 
dirty_background_ratio? That way writing to disk starts early, but the 
related apps stall waiting for I/O only when dirty_ratio is reached.


Thanks, 
Dimitris

> 
> - the file copy makes the device write congested and hence makes
>   pageout() easily blocked in get_request_wait()
> 
> As a result every application may be slowed down by the heavy swap IO
> when page fault as well as being blocked when allocating memory (which
> may go into direct reclaim and then call pageout()).
> 
> Thanks,
> Fengguang


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