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SubjectRe: [PATCH][RF C/T/D] Unmapped page cache control - via boot parameter
On 03/15/2010 08:48 PM, Anthony Liguori wrote:
> On 03/15/2010 04:27 AM, Avi Kivity wrote:
>>
>> That's only beneficial if the cache is shared. Otherwise, you could
>> use the balloon to evict cache when memory is tight.
>>
>> Shared cache is mostly a desktop thing where users run similar
>> workloads. For servers, it's much less likely. So a modified-guest
>> doesn't help a lot here.
>
> Not really. In many cloud environments, there's a set of common
> images that are instantiated on each node. Usually this is because
> you're running a horizontally scalable application or because you're
> supporting an ephemeral storage model.

But will these servers actually benefit from shared cache? So the
images are shared, they boot up, what then?

- apache really won't like serving static files from the host pagecache
- dynamic content (java, cgi) will be mostly in anonymous memory, not
pagecache
- ditto for application servers
- what else are people doing?

> In fact, with ephemeral storage, you typically want to use
> cache=writeback since you aren't providing data guarantees across
> shutdown/failure.

Interesting point.

We'd need a cache=volatile for this use case to avoid the fdatasync()s
we do now. Also useful for -snapshot. In fact I have a patch for this
somewhere I can dig out.

--
error compiling committee.c: too many arguments to function



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