svn commit: r285282 - head/sys/vm

[hiren panchasara]

On 07/08/15 at 05:46P, Alan Cox wrote:
> Author: alc
> Date: Wed Jul  8 17:45:59 2015
> New Revision: 285282
> URL: https://svnweb.freebsd.org/changeset/base/285282
> 
> Log:
>   The intention of r254304 was to scan the active queue continuously.
>   However, I've observed the active queue scan stopping when there are
>   frequent free page shortages and the inactive queue is steadily refilled
>   by other mechanisms, such as the sequential access heuristic in vm_fault()
>   or madvise(2). 

What would be the actual downside/effect of this scenario? i.e. What goes
wrong when active queue scan stops and what would I see/observe on a
system when the problem is going on - is what I want to understand.

>   To remedy this problem, record the time of the last active
>   queue scan, and always scan a number of pages proportional to the time
>   since the last scan, regardless of whether that last scan was a
>   timeout-triggered ("pass == 0") or free-page-shortage-triggered ("pass >
>   0") scan.
>   
>   Also, on a timeout-triggered scan, allow a full scan of the active queue
>   when the system is short of inactive pages.
>   
>   Reviewed by:	kib
>   MFC after:	6 weeks
>   Sponsored by:	EMC / Isilon Storage Division

[skip]

Thanks in advance.
Cheers,
Hiren
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