Re: Priority in Memory management

[Con Kolivas]

On Friday 17 March 2006 19:37, Pradeep Vincent wrote:
> I tried searching for discussions related to this but in vain A
> significant number of servers running Linux come under the category of
> "Caching Servers". These servers usually try to server data either
> from RAM or disk sub-systems and for obvious reasons want to serve as
> much data as possible from RAM. Even if the dataset is comparable to
> RAM size, other bon-performance critical activities on the system
> (such as logging, log rotation/compression, remote performance
> monitors, application code updates, security related searches )
> disturb the cache hit ratio.
>
> Mlocking the dataset is one option. Using fadvise/O_STREAM for
> everything else is another option - but this doesn't address all the
> cases.
>
> Instead of locking out all memory, being able to set priorities for
> virtual memory regions comes across as a better idea. This way if the
> system really really needs memory, kernel can reclaim the cache pages
> but not just because somebody is writing something and it might seem
> fair to reclaim the dataset cache.
>
>
> Has this come up in the past. Any history at all - I am all ears for
> ideas and concerns.

True priority support in the form of a "vm scheduler" is something I've 
mentioned many times in the past. The overhead would not be insignificant. 
Nonetheless I do have some weak priority support for page reclaiming in my 
-ck tree because doing so was not overly expensive. As far as I'm aware noone 
is currently working on a comprehensive vm scheduler.

Cheers,
Con
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